Spring 源码分析（七）--bean的加载详细分析

一：缓存中获取单例bean

    前面已经提到过，单例在Spring的同一个容器内只会被创建一次，后续再获取bean直接从单例缓存中获取，当然这里也只是尝试加载，首先尝试从缓存中加载，然后再次尝试从singletonFactories中加载。因为在创建单例bean的时候会存在依赖注入的情况，而在创建依赖的时候为了避免循环依赖，Spring创建bean的原则是不等bean创建完成就会将创建bean的ObjectFactory提早曝光加入到缓存中，一旦下一个bean创建时需要依赖上个bean,则直接使用ObjectFactory。

public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {

    /**
     * Internal marker for a null singleton object:
     * used as marker value for concurrent Maps (which don't support null values).
     */
    protected static final Object NULL_OBJECT = new Object();


    /** Logger available to subclasses */
    protected final Log logger = LogFactory.getLog(getClass());

    /** Cache of singleton objects: bean name --> bean instance */
    private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);

    /** Cache of singleton factories: bean name --> ObjectFactory */
    private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>(16);

    /** Cache of early singleton objects: bean name --> bean instance */
    private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>(16);

    /** Set of registered singletons, containing the bean names in registration order */
    private final Set<String> registeredSingletons = new LinkedHashSet<String>(256);

    /** Names of beans that are currently in creation */
    private final Set<String> singletonsCurrentlyInCreation =
            Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>(16));

    /** Names of beans currently excluded from in creation checks */
    private final Set<String> inCreationCheckExclusions =
            Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>(16));

    /** List of suppressed Exceptions, available for associating related causes */
    private Set<Exception> suppressedExceptions;

    /** Flag that indicates whether we're currently within destroySingletons */
    private boolean singletonsCurrentlyInDestruction = false;

    /** Disposable bean instances: bean name --> disposable instance */
    private final Map<String, Object> disposableBeans = new LinkedHashMap<String, Object>();

    /** Map between containing bean names: bean name --> Set of bean names that the bean contains */
    private final Map<String, Set<String>> containedBeanMap = new ConcurrentHashMap<String, Set<String>>(16);

    /** Map between dependent bean names: bean name --> Set of dependent bean names */
    private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<String, Set<String>>(64);

    /** Map between depending bean names: bean name --> Set of bean names for the bean's dependencies */
    private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<String, Set<String>>(64);


    @Override
    public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
        Assert.notNull(beanName, "'beanName' must not be null");
        synchronized (this.singletonObjects) {
            Object oldObject = this.singletonObjects.get(beanName);
            if (oldObject != null) {
                throw new IllegalStateException("Could not register object [" + singletonObject +
                        "] under bean name '" + beanName + "': there is already object [" + oldObject + "] bound");
            }
            addSingleton(beanName, singletonObject);
        }
    }

    /**
     * Add the given singleton object to the singleton cache of this factory.
     * <p>To be called for eager registration of singletons.
     * @param beanName the name of the bean
     * @param singletonObject the singleton object
     */
    protected void addSingleton(String beanName, Object singletonObject) {
        synchronized (this.singletonObjects) {
            this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
            this.singletonFactories.remove(beanName);
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.add(beanName);
        }
    }

    /**
     * Add the given singleton factory for building the specified singleton
     * if necessary.
     * <p>To be called for eager registration of singletons, e.g. to be able to
     * resolve circular references.
     * @param beanName the name of the bean
     * @param singletonFactory the factory for the singleton object
     */
    protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(singletonFactory, "Singleton factory must not be null");
        synchronized (this.singletonObjects) {
            if (!this.singletonObjects.containsKey(beanName)) {
                this.singletonFactories.put(beanName, singletonFactory);
                this.earlySingletonObjects.remove(beanName);
                this.registeredSingletons.add(beanName);
            }
        }
    }

    @Override
    public Object getSingleton(String beanName) {
        return getSingleton(beanName, true);
    }

    /**
     * Return the (raw) singleton object registered under the given name.
     * <p>Checks already instantiated singletons and also allows for an early
     * reference to a currently created singleton (resolving a circular reference).
     * @param beanName the name of the bean to look for
     * @param allowEarlyReference whether early references should be created or not
     * @return the registered singleton object, or {@code null} if none found
     */
    protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            synchronized (this.singletonObjects) {
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
                        singletonObject = singletonFactory.getObject();
                        this.earlySingletonObjects.put(beanName, singletonObject);
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
        }
        return (singletonObject != NULL_OBJECT ? singletonObject : null);
    }

    /**
     * Return the (raw) singleton object registered under the given name,
     * creating and registering a new one if none registered yet.
     * @param beanName the name of the bean
     * @param singletonFactory the ObjectFactory to lazily create the singleton
     * with, if necessary
     * @return the registered singleton object
     */
    public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(beanName, "'beanName' must not be null");
        synchronized (this.singletonObjects) {
            Object singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
                if (this.singletonsCurrentlyInDestruction) {
                    throw new BeanCreationNotAllowedException(beanName,
                            "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                            "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
                }
                beforeSingletonCreation(beanName);
                boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<Exception>();
                }
                try {
                    singletonObject = singletonFactory.getObject();
                    newSingleton = true;
                }
                catch (IllegalStateException ex) {
                    // Has the singleton object implicitly appeared in the meantime ->
                    // if yes, proceed with it since the exception indicates that state.
                    singletonObject = this.singletonObjects.get(beanName);
                    if (singletonObject == null) {
                        throw ex;
                    }
                }
                catch (BeanCreationException ex) {
                    if (recordSuppressedExceptions) {
                        for (Exception suppressedException : this.suppressedExceptions) {
                            ex.addRelatedCause(suppressedException);
                        }
                    }
                    throw ex;
                }
                finally {
                    if (recordSuppressedExceptions) {
                        this.suppressedExceptions = null;
                    }
                    afterSingletonCreation(beanName);
                }
                if (newSingleton) {
                    addSingleton(beanName, singletonObject);
                }
            }
            return (singletonObject != NULL_OBJECT ? singletonObject : null);
        }
    }

    /**
     * Register an Exception that happened to get suppressed during the creation of a
     * singleton bean instance, e.g. a temporary circular reference resolution problem.
     * @param ex the Exception to register
     */
    protected void onSuppressedException(Exception ex) {
        synchronized (this.singletonObjects) {
            if (this.suppressedExceptions != null) {
                this.suppressedExceptions.add(ex);
            }
        }
    }

    /**
     * Remove the bean with the given name from the singleton cache of this factory,
     * to be able to clean up eager registration of a singleton if creation failed.
     * @param beanName the name of the bean
     * @see #getSingletonMutex()
     */
    protected void removeSingleton(String beanName) {
        synchronized (this.singletonObjects) {
            this.singletonObjects.remove(beanName);
            this.singletonFactories.remove(beanName);
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.remove(beanName);
        }
    }

    @Override
    public boolean containsSingleton(String beanName) {
        return this.singletonObjects.containsKey(beanName);
    }

    @Override
    public String[] getSingletonNames() {
        synchronized (this.singletonObjects) {
            return StringUtils.toStringArray(this.registeredSingletons);
        }
    }

    @Override
    public int getSingletonCount() {
        synchronized (this.singletonObjects) {
            return this.registeredSingletons.size();
        }
    }


    public void setCurrentlyInCreation(String beanName, boolean inCreation) {
        Assert.notNull(beanName, "Bean name must not be null");
        if (!inCreation) {
            this.inCreationCheckExclusions.add(beanName);
        }
        else {
            this.inCreationCheckExclusions.remove(beanName);
        }
    }

    public boolean isCurrentlyInCreation(String beanName) {
        Assert.notNull(beanName, "Bean name must not be null");
        return (!this.inCreationCheckExclusions.contains(beanName) && isActuallyInCreation(beanName));
    }

    protected boolean isActuallyInCreation(String beanName) {
        return isSingletonCurrentlyInCreation(beanName);
    }

    /**
     * Return whether the specified singleton bean is currently in creation
     * (within the entire factory).
     * @param beanName the name of the bean
     */
    public boolean isSingletonCurrentlyInCreation(String beanName) {
        return this.singletonsCurrentlyInCreation.contains(beanName);
    }

    /**
     * Callback before singleton creation.
     * <p>The default implementation register the singleton as currently in creation.
     * @param beanName the name of the singleton about to be created
     * @see #isSingletonCurrentlyInCreation
     */
    protected void beforeSingletonCreation(String beanName) {
        if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }
    }

    /**
     * Callback after singleton creation.
     * <p>The default implementation marks the singleton as not in creation anymore.
     * @param beanName the name of the singleton that has been created
     * @see #isSingletonCurrentlyInCreation
     */
    protected void afterSingletonCreation(String beanName) {
        if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
            throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
        }
    }


    /**
     * Add the given bean to the list of disposable beans in this registry.
     * <p>Disposable beans usually correspond to registered singletons,
     * matching the bean name but potentially being a different instance
     * (for example, a DisposableBean adapter for a singleton that does not
     * naturally implement Spring's DisposableBean interface).
     * @param beanName the name of the bean
     * @param bean the bean instance
     */
    public void registerDisposableBean(String beanName, DisposableBean bean) {
        synchronized (this.disposableBeans) {
            this.disposableBeans.put(beanName, bean);
        }
    }

    /**
     * Register a containment relationship between two beans,
     * e.g. between an inner bean and its containing outer bean.
     * <p>Also registers the containing bean as dependent on the contained bean
     * in terms of destruction order.
     * @param containedBeanName the name of the contained (inner) bean
     * @param containingBeanName the name of the containing (outer) bean
     * @see #registerDependentBean
     */
    public void registerContainedBean(String containedBeanName, String containingBeanName) {
        // A quick check for an existing entry upfront, avoiding synchronization...
        Set<String> containedBeans = this.containedBeanMap.get(containingBeanName);
        if (containedBeans != null && containedBeans.contains(containedBeanName)) {
            return;
        }

        // No entry yet -> fully synchronized manipulation of the containedBeans Set
        synchronized (this.containedBeanMap) {
            containedBeans = this.containedBeanMap.get(containingBeanName);
            if (containedBeans == null) {
                containedBeans = new LinkedHashSet<String>(8);
                this.containedBeanMap.put(containingBeanName, containedBeans);
            }
            containedBeans.add(containedBeanName);
        }
        registerDependentBean(containedBeanName, containingBeanName);
    }

    /**
     * Register a dependent bean for the given bean,
     * to be destroyed before the given bean is destroyed.
     * @param beanName the name of the bean
     * @param dependentBeanName the name of the dependent bean
     */
    public void registerDependentBean(String beanName, String dependentBeanName) {
        // A quick check for an existing entry upfront, avoiding synchronization...
        String canonicalName = canonicalName(beanName);
        Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
        if (dependentBeans != null && dependentBeans.contains(dependentBeanName)) {
            return;
        }

        // No entry yet -> fully synchronized manipulation of the dependentBeans Set
        synchronized (this.dependentBeanMap) {
            dependentBeans = this.dependentBeanMap.get(canonicalName);
            if (dependentBeans == null) {
                dependentBeans = new LinkedHashSet<String>(8);
                this.dependentBeanMap.put(canonicalName, dependentBeans);
            }
            dependentBeans.add(dependentBeanName);
        }
        synchronized (this.dependenciesForBeanMap) {
            Set<String> dependenciesForBean = this.dependenciesForBeanMap.get(dependentBeanName);
            if (dependenciesForBean == null) {
                dependenciesForBean = new LinkedHashSet<String>(8);
                this.dependenciesForBeanMap.put(dependentBeanName, dependenciesForBean);
            }
            dependenciesForBean.add(canonicalName);
        }
    }

    /**
     * Determine whether the specified dependent bean has been registered as
     * dependent on the given bean or on any of its transitive dependencies.
     * @param beanName the name of the bean to check
     * @param dependentBeanName the name of the dependent bean
     * @since 4.0
     */
    protected boolean isDependent(String beanName, String dependentBeanName) {
        return isDependent(beanName, dependentBeanName, null);
    }

    private boolean isDependent(String beanName, String dependentBeanName, Set<String> alreadySeen) {
        if (alreadySeen != null && alreadySeen.contains(beanName)) {
            return false;
        }
        String canonicalName = canonicalName(beanName);
        Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
        if (dependentBeans == null) {
            return false;
        }
        if (dependentBeans.contains(dependentBeanName)) {
            return true;
        }
        for (String transitiveDependency : dependentBeans) {
            if (alreadySeen == null) {
                alreadySeen = new HashSet<String>();
            }
            alreadySeen.add(beanName);
            if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Determine whether a dependent bean has been registered for the given name.
     * @param beanName the name of the bean to check
     */
    protected boolean hasDependentBean(String beanName) {
        return this.dependentBeanMap.containsKey(beanName);
    }

    /**
     * Return the names of all beans which depend on the specified bean, if any.
     * @param beanName the name of the bean
     * @return the array of dependent bean names, or an empty array if none
     */
    public String[] getDependentBeans(String beanName) {
        Set<String> dependentBeans = this.dependentBeanMap.get(beanName);
        if (dependentBeans == null) {
            return new String[0];
        }
        return StringUtils.toStringArray(dependentBeans);
    }

    /**
     * Return the names of all beans that the specified bean depends on, if any.
     * @param beanName the name of the bean
     * @return the array of names of beans which the bean depends on,
     * or an empty array if none
     */
    public String[] getDependenciesForBean(String beanName) {
        Set<String> dependenciesForBean = this.dependenciesForBeanMap.get(beanName);
        if (dependenciesForBean == null) {
            return new String[0];
        }
        return dependenciesForBean.toArray(new String[dependenciesForBean.size()]);
    }

    public void destroySingletons() {
        if (logger.isDebugEnabled()) {
            logger.debug("Destroying singletons in " + this);
        }
        synchronized (this.singletonObjects) {
            this.singletonsCurrentlyInDestruction = true;
        }

        String[] disposableBeanNames;
        synchronized (this.disposableBeans) {
            disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());
        }
        for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
            destroySingleton(disposableBeanNames[i]);
        }

        this.containedBeanMap.clear();
        this.dependentBeanMap.clear();
        this.dependenciesForBeanMap.clear();

        synchronized (this.singletonObjects) {
            this.singletonObjects.clear();
            this.singletonFactories.clear();
            this.earlySingletonObjects.clear();
            this.registeredSingletons.clear();
            this.singletonsCurrentlyInDestruction = false;
        }
    }

    /**
     * Destroy the given bean. Delegates to {@code destroyBean}
     * if a corresponding disposable bean instance is found.
     * @param beanName the name of the bean
     * @see #destroyBean
     */
    public void destroySingleton(String beanName) {
        // Remove a registered singleton of the given name, if any.
        removeSingleton(beanName);

        // Destroy the corresponding DisposableBean instance.
        DisposableBean disposableBean;
        synchronized (this.disposableBeans) {
            disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
        }
        destroyBean(beanName, disposableBean);
    }

    /**
     * Destroy the given bean. Must destroy beans that depend on the given
     * bean before the bean itself. Should not throw any exceptions.
     * @param beanName the name of the bean
     * @param bean the bean instance to destroy
     */
    protected void destroyBean(String beanName, DisposableBean bean) {
        // Trigger destruction of dependent beans first...
        Set<String> dependencies = this.dependentBeanMap.remove(beanName);
        if (dependencies != null) {
            if (logger.isDebugEnabled()) {
                logger.debug("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
            }
            for (String dependentBeanName : dependencies) {
                destroySingleton(dependentBeanName);
            }
        }

        // Actually destroy the bean now...
        if (bean != null) {
            try {
                bean.destroy();
            }
            catch (Throwable ex) {
                logger.error("Destroy method on bean with name '" + beanName + "' threw an exception", ex);
            }
        }

        // Trigger destruction of contained beans...
        Set<String> containedBeans = this.containedBeanMap.remove(beanName);
        if (containedBeans != null) {
            for (String containedBeanName : containedBeans) {
                destroySingleton(containedBeanName);
            }
        }

        // Remove destroyed bean from other beans' dependencies.
        synchronized (this.dependentBeanMap) {
            for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
                Map.Entry<String, Set<String>> entry = it.next();
                Set<String> dependenciesToClean = entry.getValue();
                dependenciesToClean.remove(beanName);
                if (dependenciesToClean.isEmpty()) {
                    it.remove();
                }
            }
        }

        // Remove destroyed bean's prepared dependency information.
        this.dependenciesForBeanMap.remove(beanName);
    }

    /**
     * Exposes the singleton mutex to subclasses and external collaborators.
     * <p>Subclasses should synchronize on the given Object if they perform
     * any sort of extended singleton creation phase. In particular, subclasses
     * should <i>not</i> have their own mutexes involved in singleton creation,
     * to avoid the potential for deadlocks in lazy-init situations.
     */
    public final Object getSingletonMutex() {
        return this.singletonObjects;
    }

}

二：从bean的实例中获取对象

     在getBean方法中，getObjectForBeanInstance是个高频率使用的方法，无论是从缓存中获得bean还是根据不同的scope加载bean。总之，我们得到的bean的实例后要做的第一步就是调用这个方法来检测一下正确性，其实就是永恒检测当前bean是否是FactoryBean类型的bean，如果是，那么需要调用该bean对应的FactoryBean实例中的getObject()作为返回值。

    无论是从缓存中获取到的bean还是通过不同scope策略加载的bean都只是最原始的bean状态，并不一定是我们最终想要的bean。

（2.1）getObjectForBeanInstance

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {


/**
     * Get the object for the given bean instance, either the bean
     * instance itself or its created object in case of a FactoryBean.
     * @param beanInstance the shared bean instance
     * @param name name that may include factory dereference prefix
     * @param beanName the canonical bean name
     * @param mbd the merged bean definition
     * @return the object to expose for the bean
     */
    protected Object getObjectForBeanInstance(
            Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

        // Don't let calling code try to dereference the factory if the bean isn't a factory.
        if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
            throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
        }

        // Now we have the bean instance, which may be a normal bean or a FactoryBean.
        // If it's a FactoryBean, we use it to create a bean instance, unless the
        // caller actually wants a reference to the factory.
        if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
            return beanInstance;
        }

        Object object = null;
        if (mbd == null) {
            object = getCachedObjectForFactoryBean(beanName);
        }
        if (object == null) {
            // Return bean instance from factory.
            FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
            // Caches object obtained from FactoryBean if it is a singleton.
            if (mbd == null && containsBeanDefinition(beanName)) {
                mbd = getMergedLocalBeanDefinition(beanName);
            }
            boolean synthetic = (mbd != null && mbd.isSynthetic());
            object = getObjectFromFactoryBean(factory, beanName, !synthetic);
        }
        return object;
    }

}

    该方法所做的工作：

1. 对FactoryBean正确性的验证。
2. 对非FactoryBean不做任何处理。
3. 对bean进行转换
4. 将从Factory中解析bean的工作委托给getObjectFromFactoryBean

（2.2）getObjectFromFactoryBean

/**
 * Support base class for singleton registries which need to handle
 * {@link org.springframework.beans.factory.FactoryBean} instances,
 * integrated with {@link DefaultSingletonBeanRegistry}'s singleton management.
 *
 * <p>Serves as base class for {@link AbstractBeanFactory}.
 *
 * @author Juergen Hoeller
 * @since 2.5.1
 */
public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

    /** Cache of singleton objects created by FactoryBeans: FactoryBean name --> object */
    private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<String, Object>(16);


    /**
     * Determine the type for the given FactoryBean.
     * @param factoryBean the FactoryBean instance to check
     * @return the FactoryBean's object type,
     * or {@code null} if the type cannot be determined yet
     */
    protected Class<?> getTypeForFactoryBean(final FactoryBean<?> factoryBean) {
        try {
            if (System.getSecurityManager() != null) {
                return AccessController.doPrivileged(new PrivilegedAction<Class<?>>() {
                    @Override
                    public Class<?> run() {
                        return factoryBean.getObjectType();
                    }
                }, getAccessControlContext());
            }
            else {
                return factoryBean.getObjectType();
            }
        }
        catch (Throwable ex) {
            // Thrown from the FactoryBean's getObjectType implementation.
            logger.warn("FactoryBean threw exception from getObjectType, despite the contract saying " +
                    "that it should return null if the type of its object cannot be determined yet", ex);
            return null;
        }
    }

    /**
     * Obtain an object to expose from the given FactoryBean, if available
     * in cached form. Quick check for minimal synchronization.
     * @param beanName the name of the bean
     * @return the object obtained from the FactoryBean,
     * or {@code null} if not available
     */
    protected Object getCachedObjectForFactoryBean(String beanName) {
        Object object = this.factoryBeanObjectCache.get(beanName);
        return (object != NULL_OBJECT ? object : null);
    }

    /**
     * Obtain an object to expose from the given FactoryBean.
     * @param factory the FactoryBean instance
     * @param beanName the name of the bean
     * @param shouldPostProcess whether the bean is subject to post-processing
     * @return the object obtained from the FactoryBean
     * @throws BeanCreationException if FactoryBean object creation failed
     * @see org.springframework.beans.factory.FactoryBean#getObject()
     */
    protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
        //如果是单例模式
        if (factory.isSingleton() && containsSingleton(beanName)) {
            synchronized (getSingletonMutex()) {
                Object object = this.factoryBeanObjectCache.get(beanName);
                if (object == null) {
                    object = doGetObjectFromFactoryBean(factory, beanName);
                    // Only post-process and store if not put there already during getObject() call above
                    // (e.g. because of circular reference processing triggered by custom getBean calls)
                    Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
                    if (alreadyThere != null) {
                        object = alreadyThere;
                    }
                    else {
                        if (object != null && shouldPostProcess) {
                            try {
                                object = postProcessObjectFromFactoryBean(object, beanName);
                            }
                            catch (Throwable ex) {
                                throw new BeanCreationException(beanName,
                                        "Post-processing of FactoryBean's singleton object failed", ex);
                            }
                        }
                        this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
                    }
                }
                return (object != NULL_OBJECT ? object : null);
            }
        }
        else {
            Object object = doGetObjectFromFactoryBean(factory, beanName);
            if (object != null && shouldPostProcess) {
                try {
                    object = postProcessObjectFromFactoryBean(object, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
                }
            }
            return object;
        }
    }

    /**
     * Obtain an object to expose from the given FactoryBean.
     * @param factory the FactoryBean instance
     * @param beanName the name of the bean
     * @return the object obtained from the FactoryBean
     * @throws BeanCreationException if FactoryBean object creation failed
     * @see org.springframework.beans.factory.FactoryBean#getObject()
     */
    private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
            throws BeanCreationException {

        Object object;
        try {
            if (System.getSecurityManager() != null) {
                AccessControlContext acc = getAccessControlContext();
                try {
                    object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                        @Override
                        public Object run() throws Exception {
                                return factory.getObject();
                            }
                        }, acc);
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
                object = factory.getObject();
            }
        }
        catch (FactoryBeanNotInitializedException ex) {
            throw new BeanCurrentlyInCreationException(beanName, ex.toString());
        }
        catch (Throwable ex) {
            throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
        }

        // Do not accept a null value for a FactoryBean that's not fully
        // initialized yet: Many FactoryBeans just return null then.
        if (object == null && isSingletonCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(
                    beanName, "FactoryBean which is currently in creation returned null from getObject");
        }
        return object;
    }

    /**
     * Post-process the given object that has been obtained from the FactoryBean.
     * The resulting object will get exposed for bean references.
     * <p>The default implementation simply returns the given object as-is.
     * Subclasses may override this, for example, to apply post-processors.
     * @param object the object obtained from the FactoryBean.
     * @param beanName the name of the bean
     * @return the object to expose
     * @throws org.springframework.beans.BeansException if any post-processing failed
     */
    protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
        return object;
    }

    /**
     * Get a FactoryBean for the given bean if possible.
     * @param beanName the name of the bean
     * @param beanInstance the corresponding bean instance
     * @return the bean instance as FactoryBean
     * @throws BeansException if the given bean cannot be exposed as a FactoryBean
     */
    protected FactoryBean<?> getFactoryBean(String beanName, Object beanInstance) throws BeansException {
        if (!(beanInstance instanceof FactoryBean)) {
            throw new BeanCreationException(beanName,
                    "Bean instance of type [" + beanInstance.getClass() + "] is not a FactoryBean");
        }
        return (FactoryBean<?>) beanInstance;
    }

    /**
     * Overridden to clear the FactoryBean object cache as well.
     */
    @Override
    protected void removeSingleton(String beanName) {
        super.removeSingleton(beanName);
        this.factoryBeanObjectCache.remove(beanName);
    }

    /**
     * Returns the security context for this bean factory. If a security manager
     * is set, interaction with the user code will be executed using the privileged
     * of the security context returned by this method.
     * @see AccessController#getContext()
     */
    protected AccessControlContext getAccessControlContext() {
        return AccessController.getContext();
    }

}

三：获取单例

     如果缓存中不存在已经加载的单例bean就需要从头开始bean的加载过程了，而Spring中使用getSingleton的重载方法实现bean的加载过程。

（3.1）再次查看DefaultSingletonBeanRegistry 类中方法

/**
     * Return the (raw) singleton object registered under the given name,
     * creating and registering a new one if none registered yet.
     * @param beanName the name of the bean
     * @param singletonFactory the ObjectFactory to lazily create the singleton
     * with, if necessary
     * @return the registered singleton object
     */
    public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(beanName, "'beanName' must not be null");
        synchronized (this.singletonObjects) {
            Object singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
                if (this.singletonsCurrentlyInDestruction) {
                    throw new BeanCreationNotAllowedException(beanName,
                            "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                            "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
                }
                beforeSingletonCreation(beanName);
                boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<Exception>();
                }
                try {
                    singletonObject = singletonFactory.getObject();
                    newSingleton = true;
                }
                catch (IllegalStateException ex) {
                    // Has the singleton object implicitly appeared in the meantime ->
                    // if yes, proceed with it since the exception indicates that state.
                    singletonObject = this.singletonObjects.get(beanName);
                    if (singletonObject == null) {
                        throw ex;
                    }
                }
                catch (BeanCreationException ex) {
                    if (recordSuppressedExceptions) {
                        for (Exception suppressedException : this.suppressedExceptions) {
                            ex.addRelatedCause(suppressedException);
                        }
                    }
                    throw ex;
                }
                finally {
                    if (recordSuppressedExceptions) {
                        this.suppressedExceptions = null;
                    }
                    afterSingletonCreation(beanName);
                }
                if (newSingleton) {
                    addSingleton(beanName, singletonObject);
                }
            }
            return (singletonObject != NULL_OBJECT ? singletonObject : null);
        }
    }

分析：

（6）将结果记录至缓存并删除加载bean过程中所记录的各种辅助状态。

/**
     * Add the given singleton object to the singleton cache of this factory.
     * <p>To be called for eager registration of singletons.
     * @param beanName the name of the bean
     * @param singletonObject the singleton object
     */
    protected void addSingleton(String beanName, Object singletonObject) {
        synchronized (this.singletonObjects) {
            this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
            this.singletonFactories.remove(beanName);
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.add(beanName);
        }
    }

四：准备创建bean

（4.1）AbstractAutowireCapableBeanFactory 类

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.support;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;
import org.springframework.beans.BeansException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.PropertyAccessorUtils;
import org.springframework.beans.PropertyValue;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.TypeConverter;
import org.springframework.beans.factory.Aware;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.BeanCurrentlyInCreationException;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.UnsatisfiedDependencyException;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.beans.factory.config.ConstructorArgumentValues;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.beans.factory.config.SmartInstantiationAwareBeanPostProcessor;
import org.springframework.beans.factory.config.TypedStringValue;
import org.springframework.core.DefaultParameterNameDiscoverer;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.ParameterNameDiscoverer;
import org.springframework.core.PriorityOrdered;
import org.springframework.core.ResolvableType;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

/**
 * Abstract bean factory superclass that implements default bean creation,
 * with the full capabilities specified by the {@link RootBeanDefinition} class.
 * Implements the {@link org.springframework.beans.factory.config.AutowireCapableBeanFactory}
 * interface in addition to AbstractBeanFactory's {@link #createBean} method.
 *
 * <p>Provides bean creation (with constructor resolution), property population,
 * wiring (including autowiring), and initialization. Handles runtime bean
 * references, resolves managed collections, calls initialization methods, etc.
 * Supports autowiring constructors, properties by name, and properties by type.
 *
 * <p>The main template method to be implemented by subclasses is
 * {@link #resolveDependency(DependencyDescriptor, String, Set, TypeConverter)},
 * used for autowiring by type. In case of a factory which is capable of searching
 * its bean definitions, matching beans will typically be implemented through such
 * a search. For other factory styles, simplified matching algorithms can be implemented.
 *
 * <p>Note that this class does <i>not</i> assume or implement bean definition
 * registry capabilities. See {@link DefaultListableBeanFactory} for an implementation
 * of the {@link org.springframework.beans.factory.ListableBeanFactory} and
 * {@link BeanDefinitionRegistry} interfaces, which represent the API and SPI
 * view of such a factory, respectively.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Mark Fisher
 * @author Costin Leau
 * @author Chris Beams
 * @author Sam Brannen
 * @since 13.02.2004
 * @see RootBeanDefinition
 * @see DefaultListableBeanFactory
 * @see BeanDefinitionRegistry
 */
public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory
        implements AutowireCapableBeanFactory {

    /** Strategy for creating bean instances */
    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    /** Resolver strategy for method parameter names */
    private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();

    /** Whether to automatically try to resolve circular references between beans */
    private boolean allowCircularReferences = true;

    /**
     * Whether to resort to injecting a raw bean instance in case of circular reference,
     * even if the injected bean eventually got wrapped.
     */
    private boolean allowRawInjectionDespiteWrapping = false;

    /**
     * Dependency types to ignore on dependency check and autowire, as Set of
     * Class objects: for example, String. Default is none.
     */
    private final Set<Class<?>> ignoredDependencyTypes = new HashSet<Class<?>>();

    /**
     * Dependency interfaces to ignore on dependency check and autowire, as Set of
     * Class objects. By default, only the BeanFactory interface is ignored.
     */
    private final Set<Class<?>> ignoredDependencyInterfaces = new HashSet<Class<?>>();

    /** Cache of unfinished FactoryBean instances: FactoryBean name --> BeanWrapper */
    private final Map<String, BeanWrapper> factoryBeanInstanceCache =
            new ConcurrentHashMap<String, BeanWrapper>(16);

    /** Cache of filtered PropertyDescriptors: bean Class -> PropertyDescriptor array */
    private final ConcurrentMap<Class<?>, PropertyDescriptor[]> filteredPropertyDescriptorsCache =
            new ConcurrentHashMap<Class<?>, PropertyDescriptor[]>(256);


    /**
     * Create a new AbstractAutowireCapableBeanFactory.
     */
    public AbstractAutowireCapableBeanFactory() {
        super();
        ignoreDependencyInterface(BeanNameAware.class);
        ignoreDependencyInterface(BeanFactoryAware.class);
        ignoreDependencyInterface(BeanClassLoaderAware.class);
    }

    /**
     * Create a new AbstractAutowireCapableBeanFactory with the given parent.
     * @param parentBeanFactory parent bean factory, or {@code null} if none
     */
    public AbstractAutowireCapableBeanFactory(BeanFactory parentBeanFactory) {
        this();
        setParentBeanFactory(parentBeanFactory);
    }


    /**
     * Set the instantiation strategy to use for creating bean instances.
     * Default is CglibSubclassingInstantiationStrategy.
     * @see CglibSubclassingInstantiationStrategy
     */
    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    /**
     * Return the instantiation strategy to use for creating bean instances.
     */
    protected InstantiationStrategy getInstantiationStrategy() {
        return this.instantiationStrategy;
    }

    /**
     * Set the ParameterNameDiscoverer to use for resolving method parameter
     * names if needed (e.g. for constructor names).
     * <p>Default is a {@link DefaultParameterNameDiscoverer}.
     */
    public void setParameterNameDiscoverer(ParameterNameDiscoverer parameterNameDiscoverer) {
        this.parameterNameDiscoverer = parameterNameDiscoverer;
    }

    /**
     * Return the ParameterNameDiscoverer to use for resolving method parameter
     * names if needed.
     */
    protected ParameterNameDiscoverer getParameterNameDiscoverer() {
        return this.parameterNameDiscoverer;
    }

    /**
     * Set whether to allow circular references between beans - and automatically
     * try to resolve them.
     * <p>Note that circular reference resolution means that one of the involved beans
     * will receive a reference to another bean that is not fully initialized yet.
     * This can lead to subtle and not-so-subtle side effects on initialization;
     * it does work fine for many scenarios, though.
     * <p>Default is "true". Turn this off to throw an exception when encountering
     * a circular reference, disallowing them completely.
     * <p><b>NOTE:</b> It is generally recommended to not rely on circular references
     * between your beans. Refactor your application logic to have the two beans
     * involved delegate to a third bean that encapsulates their common logic.
     */
    public void setAllowCircularReferences(boolean allowCircularReferences) {
        this.allowCircularReferences = allowCircularReferences;
    }

    /**
     * Set whether to allow the raw injection of a bean instance into some other
     * bean's property, despite the injected bean eventually getting wrapped
     * (for example, through AOP auto-proxying).
     * <p>This will only be used as a last resort in case of a circular reference
     * that cannot be resolved otherwise: essentially, preferring a raw instance
     * getting injected over a failure of the entire bean wiring process.
     * <p>Default is "false", as of Spring 2.0. Turn this on to allow for non-wrapped
     * raw beans injected into some of your references, which was Spring 1.2's
     * (arguably unclean) default behavior.
     * <p><b>NOTE:</b> It is generally recommended to not rely on circular references
     * between your beans, in particular with auto-proxying involved.
     * @see #setAllowCircularReferences
     */
    public void setAllowRawInjectionDespiteWrapping(boolean allowRawInjectionDespiteWrapping) {
        this.allowRawInjectionDespiteWrapping = allowRawInjectionDespiteWrapping;
    }

    /**
     * Ignore the given dependency type for autowiring:
     * for example, String. Default is none.
     */
    public void ignoreDependencyType(Class<?> type) {
        this.ignoredDependencyTypes.add(type);
    }

    /**
     * Ignore the given dependency interface for autowiring.
     * <p>This will typically be used by application contexts to register
     * dependencies that are resolved in other ways, like BeanFactory through
     * BeanFactoryAware or ApplicationContext through ApplicationContextAware.
     * <p>By default, only the BeanFactoryAware interface is ignored.
     * For further types to ignore, invoke this method for each type.
     * @see org.springframework.beans.factory.BeanFactoryAware
     * @see org.springframework.context.ApplicationContextAware
     */
    public void ignoreDependencyInterface(Class<?> ifc) {
        this.ignoredDependencyInterfaces.add(ifc);
    }

    @Override
    public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
        super.copyConfigurationFrom(otherFactory);
        if (otherFactory instanceof AbstractAutowireCapableBeanFactory) {
            AbstractAutowireCapableBeanFactory otherAutowireFactory =
                    (AbstractAutowireCapableBeanFactory) otherFactory;
            this.instantiationStrategy = otherAutowireFactory.instantiationStrategy;
            this.allowCircularReferences = otherAutowireFactory.allowCircularReferences;
            this.ignoredDependencyTypes.addAll(otherAutowireFactory.ignoredDependencyTypes);
            this.ignoredDependencyInterfaces.addAll(otherAutowireFactory.ignoredDependencyInterfaces);
        }
    }


    //-------------------------------------------------------------------------
    // Typical methods for creating and populating external bean instances
    //-------------------------------------------------------------------------

    @Override
    @SuppressWarnings("unchecked")
    public <T> T createBean(Class<T> beanClass) throws BeansException {
        // Use prototype bean definition, to avoid registering bean as dependent bean.
        RootBeanDefinition bd = new RootBeanDefinition(beanClass);
        bd.setScope(SCOPE_PROTOTYPE);
        bd.allowCaching = ClassUtils.isCacheSafe(beanClass, getBeanClassLoader());
        return (T) createBean(beanClass.getName(), bd, null);
    }

    @Override
    public void autowireBean(Object existingBean) {
        // Use non-singleton bean definition, to avoid registering bean as dependent bean.
        RootBeanDefinition bd = new RootBeanDefinition(ClassUtils.getUserClass(existingBean));
        bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
        bd.allowCaching = ClassUtils.isCacheSafe(bd.getBeanClass(), getBeanClassLoader());
        BeanWrapper bw = new BeanWrapperImpl(existingBean);
        initBeanWrapper(bw);
        populateBean(bd.getBeanClass().getName(), bd, bw);
    }

    @Override
    public Object configureBean(Object existingBean, String beanName) throws BeansException {
        markBeanAsCreated(beanName);
        BeanDefinition mbd = getMergedBeanDefinition(beanName);
        RootBeanDefinition bd = null;
        if (mbd instanceof RootBeanDefinition) {
            RootBeanDefinition rbd = (RootBeanDefinition) mbd;
            bd = (rbd.isPrototype() ? rbd : rbd.cloneBeanDefinition());
        }
        if (!mbd.isPrototype()) {
            if (bd == null) {
                bd = new RootBeanDefinition(mbd);
            }
            bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
            bd.allowCaching = ClassUtils.isCacheSafe(ClassUtils.getUserClass(existingBean), getBeanClassLoader());
        }
        BeanWrapper bw = new BeanWrapperImpl(existingBean);
        initBeanWrapper(bw);
        populateBean(beanName, bd, bw);
        return initializeBean(beanName, existingBean, bd);
    }

    @Override
    public Object resolveDependency(DependencyDescriptor descriptor, String requestingBeanName) throws BeansException {
        return resolveDependency(descriptor, requestingBeanName, null, null);
    }


    //-------------------------------------------------------------------------
    // Specialized methods for fine-grained control over the bean lifecycle
    //-------------------------------------------------------------------------

    @Override
    public Object createBean(Class<?> beanClass, int autowireMode, boolean dependencyCheck) throws BeansException {
        // Use non-singleton bean definition, to avoid registering bean as dependent bean.
        RootBeanDefinition bd = new RootBeanDefinition(beanClass, autowireMode, dependencyCheck);
        bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
        return createBean(beanClass.getName(), bd, null);
    }

    @Override
    public Object autowire(Class<?> beanClass, int autowireMode, boolean dependencyCheck) throws BeansException {
        // Use non-singleton bean definition, to avoid registering bean as dependent bean.
        final RootBeanDefinition bd = new RootBeanDefinition(beanClass, autowireMode, dependencyCheck);
        bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
        if (bd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR) {
            return autowireConstructor(beanClass.getName(), bd, null, null).getWrappedInstance();
        }
        else {
            Object bean;
            final BeanFactory parent = this;
            if (System.getSecurityManager() != null) {
                bean = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    @Override
                    public Object run() {
                        return getInstantiationStrategy().instantiate(bd, null, parent);
                    }
                }, getAccessControlContext());
            }
            else {
                bean = getInstantiationStrategy().instantiate(bd, null, parent);
            }
            populateBean(beanClass.getName(), bd, new BeanWrapperImpl(bean));
            return bean;
        }
    }

    @Override
    public void autowireBeanProperties(Object existingBean, int autowireMode, boolean dependencyCheck)
            throws BeansException {

        if (autowireMode == AUTOWIRE_CONSTRUCTOR) {
            throw new IllegalArgumentException("AUTOWIRE_CONSTRUCTOR not supported for existing bean instance");
        }
        // Use non-singleton bean definition, to avoid registering bean as dependent bean.
        RootBeanDefinition bd =
                new RootBeanDefinition(ClassUtils.getUserClass(existingBean), autowireMode, dependencyCheck);
        bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
        BeanWrapper bw = new BeanWrapperImpl(existingBean);
        initBeanWrapper(bw);
        populateBean(bd.getBeanClass().getName(), bd, bw);
    }

    @Override
    public void applyBeanPropertyValues(Object existingBean, String beanName) throws BeansException {
        markBeanAsCreated(beanName);
        BeanDefinition bd = getMergedBeanDefinition(beanName);
        BeanWrapper bw = new BeanWrapperImpl(existingBean);
        initBeanWrapper(bw);
        applyPropertyValues(beanName, bd, bw, bd.getPropertyValues());
    }

    @Override
    public Object initializeBean(Object existingBean, String beanName) {
        return initializeBean(beanName, existingBean, null);
    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            result = beanProcessor.postProcessBeforeInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

    @Override
    public void destroyBean(Object existingBean) {
        new DisposableBeanAdapter(existingBean, getBeanPostProcessors(), getAccessControlContext()).destroy();
    }


    //---------------------------------------------------------------------
    // Implementation of relevant AbstractBeanFactory template methods
    //---------------------------------------------------------------------

    /**
     * Central method of this class: creates a bean instance,
     * populates the bean instance, applies post-processors, etc.
     * @see #doCreateBean
     */
    @Override
    protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        RootBeanDefinition mbdToUse = mbd;

        // Make sure bean class is actually resolved at this point, and
        // clone the bean definition in case of a dynamically resolved Class
        // which cannot be stored in the shared merged bean definition.
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

    /**
     * Actually create the specified bean. Pre-creation processing has already happened
     * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
     * <p>Differentiates between default bean instantiation, use of a
     * factory method, and autowiring a constructor.
     * @param beanName the name of the bean
     * @param mbd the merged bean definition for the bean
     * @param args explicit arguments to use for constructor or factory method invocation
     * @return a new instance of the bean
     * @throws BeanCreationException if the bean could not be created
     * @see #instantiateBean
     * @see #instantiateUsingFactoryMethod
     * @see #autowireConstructor
     */
    protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
        mbd.resolvedTargetType = beanType;

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                try {
                    applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "Post-processing of merged bean definition failed", ex);
                }
                mbd.postProcessed = true;
            }
        }

        // Eagerly cache singletons to be able to resolve circular references
        // even when triggered by lifecycle interfaces like BeanFactoryAware.
        boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
                isSingletonCurrentlyInCreation(beanName));
        if (earlySingletonExposure) {
            if (logger.isDebugEnabled()) {
                logger.debug("Eagerly caching bean '" + beanName +
                        "' to allow for resolving potential circular references");
            }
            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }

        if (earlySingletonExposure) {
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
                    for (String dependentBean : dependentBeans) {
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name '" + beanName + "' has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        try {
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

    @Override
    protected Class<?> predictBeanType(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
        Class<?> targetType = determineTargetType(beanName, mbd, typesToMatch);

        // Apply SmartInstantiationAwareBeanPostProcessors to predict the
        // eventual type after a before-instantiation shortcut.
        if (targetType != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                    SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
                    Class<?> predicted = ibp.predictBeanType(targetType, beanName);
                    if (predicted != null && (typesToMatch.length != 1 || FactoryBean.class != typesToMatch[0] ||
                            FactoryBean.class.isAssignableFrom(predicted))) {
                        return predicted;
                    }
                }
            }
        }
        return targetType;
    }

    /**
     * Determine the target type for the given bean definition.
     * @param beanName the name of the bean (for error handling purposes)
     * @param mbd the merged bean definition for the bean
     * @param typesToMatch the types to match in case of internal type matching purposes
     * (also signals that the returned {@code Class} will never be exposed to application code)
     * @return the type for the bean if determinable, or {@code null} otherwise
     */
    protected Class<?> determineTargetType(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
        Class<?> targetType = mbd.getTargetType();
        if (targetType == null) {
            targetType = (mbd.getFactoryMethodName() != null ?
                    getTypeForFactoryMethod(beanName, mbd, typesToMatch) :
                    resolveBeanClass(mbd, beanName, typesToMatch));
            if (ObjectUtils.isEmpty(typesToMatch) || getTempClassLoader() == null) {
                mbd.resolvedTargetType = targetType;
            }
        }
        return targetType;
    }

    /**
     * Determine the target type for the given bean definition which is based on
     * a factory method. Only called if there is no singleton instance registered
     * for the target bean already.
     * <p>This implementation determines the type matching {@link #createBean}'s
     * different creation strategies. As far as possible, we'll perform static
     * type checking to avoid creation of the target bean.
     * @param beanName the name of the bean (for error handling purposes)
     * @param mbd the merged bean definition for the bean
     * @param typesToMatch the types to match in case of internal type matching purposes
     * (also signals that the returned {@code Class} will never be exposed to application code)
     * @return the type for the bean if determinable, or {@code null} otherwise
     * @see #createBean
     */
    protected Class<?> getTypeForFactoryMethod(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
        ResolvableType cachedReturnType = mbd.factoryMethodReturnType;
        if (cachedReturnType != null) {
            return cachedReturnType.resolve();
        }

        Class<?> factoryClass;
        boolean isStatic = true;

        String factoryBeanName = mbd.getFactoryBeanName();
        if (factoryBeanName != null) {
            if (factoryBeanName.equals(beanName)) {
                throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
                        "factory-bean reference points back to the same bean definition");
            }
            // Check declared factory method return type on factory class.
            factoryClass = getType(factoryBeanName);
            isStatic = false;
        }
        else {
            // Check declared factory method return type on bean class.
            factoryClass = resolveBeanClass(mbd, beanName, typesToMatch);
        }

        if (factoryClass == null) {
            return null;
        }
        factoryClass = ClassUtils.getUserClass(factoryClass);

        // If all factory methods have the same return type, return that type.
        // Can't clearly figure out exact method due to type converting / autowiring!
        Class<?> commonType = null;
        Method uniqueCandidate = null;
        int minNrOfArgs = mbd.getConstructorArgumentValues().getArgumentCount();
        Method[] candidates = ReflectionUtils.getUniqueDeclaredMethods(factoryClass);
        for (Method factoryMethod : candidates) {
            if (Modifier.isStatic(factoryMethod.getModifiers()) == isStatic &&
                    factoryMethod.getName().equals(mbd.getFactoryMethodName()) &&
                    factoryMethod.getParameterTypes().length >= minNrOfArgs) {
                // Declared type variables to inspect?
                if (factoryMethod.getTypeParameters().length > 0) {
                    try {
                        // Fully resolve parameter names and argument values.
                        Class<?>[] paramTypes = factoryMethod.getParameterTypes();
                        String[] paramNames = null;
                        ParameterNameDiscoverer pnd = getParameterNameDiscoverer();
                        if (pnd != null) {
                            paramNames = pnd.getParameterNames(factoryMethod);
                        }
                        ConstructorArgumentValues cav = mbd.getConstructorArgumentValues();
                        Set<ConstructorArgumentValues.ValueHolder> usedValueHolders =
                                new HashSet<ConstructorArgumentValues.ValueHolder>(paramTypes.length);
                        Object[] args = new Object[paramTypes.length];
                        for (int i = 0; i < args.length; i++) {
                            ConstructorArgumentValues.ValueHolder valueHolder = cav.getArgumentValue(
                                    i, paramTypes[i], (paramNames != null ? paramNames[i] : null), usedValueHolders);
                            if (valueHolder == null) {
                                valueHolder = cav.getGenericArgumentValue(null, null, usedValueHolders);
                            }
                            if (valueHolder != null) {
                                args[i] = valueHolder.getValue();
                                usedValueHolders.add(valueHolder);
                            }
                        }
                        Class<?> returnType = AutowireUtils.resolveReturnTypeForFactoryMethod(
                                factoryMethod, args, getBeanClassLoader());
                        if (returnType != null) {
                            uniqueCandidate = (commonType == null ? factoryMethod : null);
                            commonType = ClassUtils.determineCommonAncestor(returnType, commonType);
                            if (commonType == null) {
                                // Ambiguous return types found: return null to indicate "not determinable".
                                return null;
                            }
                        }
                    }
                    catch (Throwable ex) {
                        if (logger.isDebugEnabled()) {
                            logger.debug("Failed to resolve generic return type for factory method: " + ex);
                        }
                    }
                }
                else {
                    uniqueCandidate = (commonType == null ? factoryMethod : null);
                    commonType = ClassUtils.determineCommonAncestor(factoryMethod.getReturnType(), commonType);
                    if (commonType == null) {
                        // Ambiguous return types found: return null to indicate "not determinable".
                        return null;
                    }
                }
            }
        }

        if (commonType != null) {
            // Clear return type found: all factory methods return same type.
            mbd.factoryMethodReturnType = (uniqueCandidate != null ?
                    ResolvableType.forMethodReturnType(uniqueCandidate) : ResolvableType.forClass(commonType));
        }
        return commonType;
    }

    /**
     * This implementation attempts to query the FactoryBean's generic parameter metadata
     * if present to determine the object type. If not present, i.e. the FactoryBean is
     * declared as a raw type, checks the FactoryBean's {@code getObjectType} method
     * on a plain instance of the FactoryBean, without bean properties applied yet.
     * If this doesn't return a type yet, a full creation of the FactoryBean is
     * used as fallback (through delegation to the superclass's implementation).
     * <p>The shortcut check for a FactoryBean is only applied in case of a singleton
     * FactoryBean. If the FactoryBean instance itself is not kept as singleton,
     * it will be fully created to check the type of its exposed object.
     */
    @Override
    protected Class<?> getTypeForFactoryBean(String beanName, RootBeanDefinition mbd) {
        String factoryBeanName = mbd.getFactoryBeanName();
        String factoryMethodName = mbd.getFactoryMethodName();

        if (factoryBeanName != null) {
            if (factoryMethodName != null) {
                // Try to obtain the FactoryBean's object type from its factory method declaration
                // without instantiating the containing bean at all.
                BeanDefinition fbDef = getBeanDefinition(factoryBeanName);
                if (fbDef instanceof AbstractBeanDefinition) {
                    AbstractBeanDefinition afbDef = (AbstractBeanDefinition) fbDef;
                    if (afbDef.hasBeanClass()) {
                        Class<?> result = getTypeForFactoryBeanFromMethod(afbDef.getBeanClass(), factoryMethodName);
                        if (result != null) {
                            return result;
                        }
                    }
                }
            }
            // If not resolvable above and the referenced factory bean doesn't exist yet,
            // exit here - we don't want to force the creation of another bean just to
            // obtain a FactoryBean's object type...
            if (!isBeanEligibleForMetadataCaching(factoryBeanName)) {
                return null;
            }
        }

        // Let's obtain a shortcut instance for an early getObjectType() call...
        FactoryBean<?> fb = (mbd.isSingleton() ?
                getSingletonFactoryBeanForTypeCheck(beanName, mbd) :
                getNonSingletonFactoryBeanForTypeCheck(beanName, mbd));

        if (fb != null) {
            // Try to obtain the FactoryBean's object type from this early stage of the instance.
            Class<?> result = getTypeForFactoryBean(fb);
            if (result != null) {
                return result;
            }
            else {
                // No type found for shortcut FactoryBean instance:
                // fall back to full creation of the FactoryBean instance.
                return super.getTypeForFactoryBean(beanName, mbd);
            }
        }

        if (factoryBeanName == null && mbd.hasBeanClass()) {
            // No early bean instantiation possible: determine FactoryBean's type from
            // static factory method signature or from class inheritance hierarchy...
            if (factoryMethodName != null) {
                return getTypeForFactoryBeanFromMethod(mbd.getBeanClass(), factoryMethodName);
            }
            else {
                return GenericTypeResolver.resolveTypeArgument(mbd.getBeanClass(), FactoryBean.class);
            }
        }

        return null;
    }

    /**
     * Introspect the factory method signatures on the given bean class,
     * trying to find a common {@code FactoryBean} object type declared there.
     * @param beanClass the bean class to find the factory method on
     * @param factoryMethodName the name of the factory method
     * @return the common {@code FactoryBean} object type, or {@code null} if none
     */
    private Class<?> getTypeForFactoryBeanFromMethod(Class<?> beanClass, final String factoryMethodName) {
        class Holder { Class<?> value = null; }
        final Holder objectType = new Holder();

        // CGLIB subclass methods hide generic parameters; look at the original user class.
        Class<?> fbClass = ClassUtils.getUserClass(beanClass);

        // Find the given factory method, taking into account that in the case of
        // @Bean methods, there may be parameters present.
        ReflectionUtils.doWithMethods(fbClass,
                new ReflectionUtils.MethodCallback() {
                    @Override
                    public void doWith(Method method) {
                        if (method.getName().equals(factoryMethodName) &&
                                FactoryBean.class.isAssignableFrom(method.getReturnType())) {
                            Class<?> currentType = GenericTypeResolver.resolveReturnTypeArgument(
                                    method, FactoryBean.class);
                            if (currentType != null) {
                                objectType.value = ClassUtils.determineCommonAncestor(currentType, objectType.value);
                            }
                        }
                    }
                });

        return (objectType.value != null && Object.class != objectType.value ? objectType.value : null);
    }

    /**
     * Obtain a reference for early access to the specified bean,
     * typically for the purpose of resolving a circular reference.
     * @param beanName the name of the bean (for error handling purposes)
     * @param mbd the merged bean definition for the bean
     * @param bean the raw bean instance
     * @return the object to expose as bean reference
     */
    protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
        Object exposedObject = bean;
        if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                    SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
                    exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
                    if (exposedObject == null) {
                        return null;
                    }
                }
            }
        }
        return exposedObject;
    }


    //---------------------------------------------------------------------
    // Implementation methods
    //---------------------------------------------------------------------

    /**
     * Obtain a "shortcut" singleton FactoryBean instance to use for a
     * {@code getObjectType()} call, without full initialization of the FactoryBean.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return the FactoryBean instance, or {@code null} to indicate
     * that we couldn't obtain a shortcut FactoryBean instance
     */
    private FactoryBean<?> getSingletonFactoryBeanForTypeCheck(String beanName, RootBeanDefinition mbd) {
        synchronized (getSingletonMutex()) {
            BeanWrapper bw = this.factoryBeanInstanceCache.get(beanName);
            if (bw != null) {
                return (FactoryBean<?>) bw.getWrappedInstance();
            }
            if (isSingletonCurrentlyInCreation(beanName) ||
                    (mbd.getFactoryBeanName() != null && isSingletonCurrentlyInCreation(mbd.getFactoryBeanName()))) {
                return null;
            }

            Object instance = null;
            try {
                // Mark this bean as currently in creation, even if just partially.
                beforeSingletonCreation(beanName);
                // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
                instance = resolveBeforeInstantiation(beanName, mbd);
                if (instance == null) {
                    bw = createBeanInstance(beanName, mbd, null);
                    instance = bw.getWrappedInstance();
                }
            }
            finally {
                // Finished partial creation of this bean.
                afterSingletonCreation(beanName);
            }

            FactoryBean<?> fb = getFactoryBean(beanName, instance);
            if (bw != null) {
                this.factoryBeanInstanceCache.put(beanName, bw);
            }
            return fb;
        }
    }

    /**
     * Obtain a "shortcut" non-singleton FactoryBean instance to use for a
     * {@code getObjectType()} call, without full initialization of the FactoryBean.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return the FactoryBean instance, or {@code null} to indicate
     * that we couldn't obtain a shortcut FactoryBean instance
     */
    private FactoryBean<?> getNonSingletonFactoryBeanForTypeCheck(String beanName, RootBeanDefinition mbd) {
        if (isPrototypeCurrentlyInCreation(beanName)) {
            return null;
        }

        Object instance = null;
        try {
            // Mark this bean as currently in creation, even if just partially.
            beforePrototypeCreation(beanName);
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            instance = resolveBeforeInstantiation(beanName, mbd);
            if (instance == null) {
                BeanWrapper bw = createBeanInstance(beanName, mbd, null);
                instance = bw.getWrappedInstance();
            }
        }
        catch (BeanCreationException ex) {
            // Can only happen when getting a FactoryBean.
            if (logger.isDebugEnabled()) {
                logger.debug("Bean creation exception on non-singleton FactoryBean type check: " + ex);
            }
            onSuppressedException(ex);
            return null;
        }
        finally {
            // Finished partial creation of this bean.
            afterPrototypeCreation(beanName);
        }

        return getFactoryBean(beanName, instance);
    }

    /**
     * Apply MergedBeanDefinitionPostProcessors to the specified bean definition,
     * invoking their {@code postProcessMergedBeanDefinition} methods.
     * @param mbd the merged bean definition for the bean
     * @param beanType the actual type of the managed bean instance
     * @param beanName the name of the bean
     * @see MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition
     */
    protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof MergedBeanDefinitionPostProcessor) {
                MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
                bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
            }
        }
    }

    /**
     * Apply before-instantiation post-processors, resolving whether there is a
     * before-instantiation shortcut for the specified bean.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return the shortcut-determined bean instance, or {@code null} if none
     */
    protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
        Object bean = null;
        if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
            // Make sure bean class is actually resolved at this point.
            if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
                Class<?> targetType = determineTargetType(beanName, mbd);
                if (targetType != null) {
                    bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                    if (bean != null) {
                        bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                    }
                }
            }
            mbd.beforeInstantiationResolved = (bean != null);
        }
        return bean;
    }

    /**
     * Apply InstantiationAwareBeanPostProcessors to the specified bean definition
     * (by class and name), invoking their {@code postProcessBeforeInstantiation} methods.
     * <p>Any returned object will be used as the bean instead of actually instantiating
     * the target bean. A {@code null} return value from the post-processor will
     * result in the target bean being instantiated.
     * @param beanClass the class of the bean to be instantiated
     * @param beanName the name of the bean
     * @return the bean object to use instead of a default instance of the target bean, or {@code null}
     * @see InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation
     */
    protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
                if (result != null) {
                    return result;
                }
            }
        }
        return null;
    }

    /**
     * Create a new instance for the specified bean, using an appropriate instantiation strategy:
     * factory method, constructor autowiring, or simple instantiation.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param args explicit arguments to use for constructor or factory method invocation
     * @return BeanWrapper for the new instance
     * @see #instantiateUsingFactoryMethod
     * @see #autowireConstructor
     * @see #instantiateBean
     */
    protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
        // Make sure bean class is actually resolved at this point.
        Class<?> beanClass = resolveBeanClass(mbd, beanName);

        if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
        }

        if (mbd.getFactoryMethodName() != null)  {
            return instantiateUsingFactoryMethod(beanName, mbd, args);
        }

        // Shortcut when re-creating the same bean...
        boolean resolved = false;
        boolean autowireNecessary = false;
        if (args == null) {
            synchronized (mbd.constructorArgumentLock) {
                if (mbd.resolvedConstructorOrFactoryMethod != null) {
                    resolved = true;
                    autowireNecessary = mbd.constructorArgumentsResolved;
                }
            }
        }
        if (resolved) {
            if (autowireNecessary) {
                return autowireConstructor(beanName, mbd, null, null);
            }
            else {
                return instantiateBean(beanName, mbd);
            }
        }

        // Need to determine the constructor...
        Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
        if (ctors != null ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
                mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
            return autowireConstructor(beanName, mbd, ctors, args);
        }

        // No special handling: simply use no-arg constructor.
        return instantiateBean(beanName, mbd);
    }

    /**
     * Determine candidate constructors to use for the given bean, checking all registered
     * {@link SmartInstantiationAwareBeanPostProcessor SmartInstantiationAwareBeanPostProcessors}.
     * @param beanClass the raw class of the bean
     * @param beanName the name of the bean
     * @return the candidate constructors, or {@code null} if none specified
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.config.SmartInstantiationAwareBeanPostProcessor#determineCandidateConstructors
     */
    protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(Class<?> beanClass, String beanName)
            throws BeansException {

        if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                    SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
                    Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
                    if (ctors != null) {
                        return ctors;
                    }
                }
            }
        }
        return null;
    }

    /**
     * Instantiate the given bean using its default constructor.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return BeanWrapper for the new instance
     */
    protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
        try {
            Object beanInstance;
            final BeanFactory parent = this;
            if (System.getSecurityManager() != null) {
                beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    @Override
                    public Object run() {
                        return getInstantiationStrategy().instantiate(mbd, beanName, parent);
                    }
                }, getAccessControlContext());
            }
            else {
                beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
            }
            BeanWrapper bw = new BeanWrapperImpl(beanInstance);
            initBeanWrapper(bw);
            return bw;
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
        }
    }

    /**
     * Instantiate the bean using a named factory method. The method may be static, if the
     * mbd parameter specifies a class, rather than a factoryBean, or an instance variable
     * on a factory object itself configured using Dependency Injection.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param explicitArgs argument values passed in programmatically via the getBean method,
     * or {@code null} if none (-> use constructor argument values from bean definition)
     * @return BeanWrapper for the new instance
     * @see #getBean(String, Object[])
     */
    protected BeanWrapper instantiateUsingFactoryMethod(
            String beanName, RootBeanDefinition mbd, Object[] explicitArgs) {

        return new ConstructorResolver(this).instantiateUsingFactoryMethod(beanName, mbd, explicitArgs);
    }

    /**
     * "autowire constructor" (with constructor arguments by type) behavior.
     * Also applied if explicit constructor argument values are specified,
     * matching all remaining arguments with beans from the bean factory.
     * <p>This corresponds to constructor injection: In this mode, a Spring
     * bean factory is able to host components that expect constructor-based
     * dependency resolution.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param ctors the chosen candidate constructors
     * @param explicitArgs argument values passed in programmatically via the getBean method,
     * or {@code null} if none (-> use constructor argument values from bean definition)
     * @return BeanWrapper for the new instance
     */
    protected BeanWrapper autowireConstructor(
            String beanName, RootBeanDefinition mbd, Constructor<?>[] ctors, Object[] explicitArgs) {

        return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
    }

    /**
     * Populate the bean instance in the given BeanWrapper with the property values
     * from the bean definition.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param bw BeanWrapper with bean instance
     */
    protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
        PropertyValues pvs = mbd.getPropertyValues();

        if (bw == null) {
            if (!pvs.isEmpty()) {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
            }
            else {
                // Skip property population phase for null instance.
                return;
            }
        }

        // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
        // state of the bean before properties are set. This can be used, for example,
        // to support styles of field injection.
        boolean continueWithPropertyPopulation = true;

        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                        continueWithPropertyPopulation = false;
                        break;
                    }
                }
            }
        }

        if (!continueWithPropertyPopulation) {
            return;
        }

        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

            // Add property values based on autowire by name if applicable.
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
                autowireByName(beanName, mbd, bw, newPvs);
            }

            // Add property values based on autowire by type if applicable.
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
                autowireByType(beanName, mbd, bw, newPvs);
            }

            pvs = newPvs;
        }

        boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
        boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

        if (hasInstAwareBpps || needsDepCheck) {
            PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
            if (hasInstAwareBpps) {
                for (BeanPostProcessor bp : getBeanPostProcessors()) {
                    if (bp instanceof InstantiationAwareBeanPostProcessor) {
                        InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                        pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                        if (pvs == null) {
                            return;
                        }
                    }
                }
            }
            if (needsDepCheck) {
                checkDependencies(beanName, mbd, filteredPds, pvs);
            }
        }

        applyPropertyValues(beanName, mbd, bw, pvs);
    }

    /**
     * Fill in any missing property values with references to
     * other beans in this factory if autowire is set to "byName".
     * @param beanName the name of the bean we're wiring up.
     * Useful for debugging messages; not used functionally.
     * @param mbd bean definition to update through autowiring
     * @param bw BeanWrapper from which we can obtain information about the bean
     * @param pvs the PropertyValues to register wired objects with
     */
    protected void autowireByName(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
            if (containsBean(propertyName)) {
                Object bean = getBean(propertyName);
                pvs.add(propertyName, bean);
                registerDependentBean(propertyName, beanName);
                if (logger.isDebugEnabled()) {
                    logger.debug("Added autowiring by name from bean name '" + beanName +
                            "' via property '" + propertyName + "' to bean named '" + propertyName + "'");
                }
            }
            else {
                if (logger.isTraceEnabled()) {
                    logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
                            "' by name: no matching bean found");
                }
            }
        }
    }

    /**
     * Abstract method defining "autowire by type" (bean properties by type) behavior.
     * <p>This is like PicoContainer default, in which there must be exactly one bean
     * of the property type in the bean factory. This makes bean factories simple to
     * configure for small namespaces, but doesn't work as well as standard Spring
     * behavior for bigger applications.
     * @param beanName the name of the bean to autowire by type
     * @param mbd the merged bean definition to update through autowiring
     * @param bw BeanWrapper from which we can obtain information about the bean
     * @param pvs the PropertyValues to register wired objects with
     */
    protected void autowireByType(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
            converter = bw;
        }

        Set<String> autowiredBeanNames = new LinkedHashSet<String>(4);
        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
            try {
                PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
                // Don't try autowiring by type for type Object: never makes sense,
                // even if it technically is a unsatisfied, non-simple property.
                if (Object.class != pd.getPropertyType()) {
                    MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
                    // Do not allow eager init for type matching in case of a prioritized post-processor.
                    boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());
                    DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
                    Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
                    if (autowiredArgument != null) {
                        pvs.add(propertyName, autowiredArgument);
                    }
                    for (String autowiredBeanName : autowiredBeanNames) {
                        registerDependentBean(autowiredBeanName, beanName);
                        if (logger.isDebugEnabled()) {
                            logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" +
                                    propertyName + "' to bean named '" + autowiredBeanName + "'");
                        }
                    }
                    autowiredBeanNames.clear();
                }
            }
            catch (BeansException ex) {
                throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
            }
        }
    }


    /**
     * Return an array of non-simple bean properties that are unsatisfied.
     * These are probably unsatisfied references to other beans in the
     * factory. Does not include simple properties like primitives or Strings.
     * @param mbd the merged bean definition the bean was created with
     * @param bw the BeanWrapper the bean was created with
     * @return an array of bean property names
     * @see org.springframework.beans.BeanUtils#isSimpleProperty
     */
    protected String[] unsatisfiedNonSimpleProperties(AbstractBeanDefinition mbd, BeanWrapper bw) {
        Set<String> result = new TreeSet<String>();
        PropertyValues pvs = mbd.getPropertyValues();
        PropertyDescriptor[] pds = bw.getPropertyDescriptors();
        for (PropertyDescriptor pd : pds) {
            if (pd.getWriteMethod() != null && !isExcludedFromDependencyCheck(pd) && !pvs.contains(pd.getName()) &&
                    !BeanUtils.isSimpleProperty(pd.getPropertyType())) {
                result.add(pd.getName());
            }
        }
        return StringUtils.toStringArray(result);
    }

    /**
     * Extract a filtered set of PropertyDescriptors from the given BeanWrapper,
     * excluding ignored dependency types or properties defined on ignored dependency interfaces.
     * @param bw the BeanWrapper the bean was created with
     * @param cache whether to cache filtered PropertyDescriptors for the given bean Class
     * @return the filtered PropertyDescriptors
     * @see #isExcludedFromDependencyCheck
     * @see #filterPropertyDescriptorsForDependencyCheck(org.springframework.beans.BeanWrapper)
     */
    protected PropertyDescriptor[] filterPropertyDescriptorsForDependencyCheck(BeanWrapper bw, boolean cache) {
        PropertyDescriptor[] filtered = this.filteredPropertyDescriptorsCache.get(bw.getWrappedClass());
        if (filtered == null) {
            filtered = filterPropertyDescriptorsForDependencyCheck(bw);
            if (cache) {
                PropertyDescriptor[] existing =
                        this.filteredPropertyDescriptorsCache.putIfAbsent(bw.getWrappedClass(), filtered);
                if (existing != null) {
                    filtered = existing;
                }
            }
        }
        return filtered;
    }

    /**
     * Extract a filtered set of PropertyDescriptors from the given BeanWrapper,
     * excluding ignored dependency types or properties defined on ignored dependency interfaces.
     * @param bw the BeanWrapper the bean was created with
     * @return the filtered PropertyDescriptors
     * @see #isExcludedFromDependencyCheck
     */
    protected PropertyDescriptor[] filterPropertyDescriptorsForDependencyCheck(BeanWrapper bw) {
        List<PropertyDescriptor> pds =
                new LinkedList<PropertyDescriptor>(Arrays.asList(bw.getPropertyDescriptors()));
        for (Iterator<PropertyDescriptor> it = pds.iterator(); it.hasNext();) {
            PropertyDescriptor pd = it.next();
            if (isExcludedFromDependencyCheck(pd)) {
                it.remove();
            }
        }
        return pds.toArray(new PropertyDescriptor[pds.size()]);
    }

    /**
     * Determine whether the given bean property is excluded from dependency checks.
     * <p>This implementation excludes properties defined by CGLIB and
     * properties whose type matches an ignored dependency type or which
     * are defined by an ignored dependency interface.
     * @param pd the PropertyDescriptor of the bean property
     * @return whether the bean property is excluded
     * @see #ignoreDependencyType(Class)
     * @see #ignoreDependencyInterface(Class)
     */
    protected boolean isExcludedFromDependencyCheck(PropertyDescriptor pd) {
        return (AutowireUtils.isExcludedFromDependencyCheck(pd) ||
                this.ignoredDependencyTypes.contains(pd.getPropertyType()) ||
                AutowireUtils.isSetterDefinedInInterface(pd, this.ignoredDependencyInterfaces));
    }

    /**
     * Perform a dependency check that all properties exposed have been set,
     * if desired. Dependency checks can be objects (collaborating beans),
     * simple (primitives and String), or all (both).
     * @param beanName the name of the bean
     * @param mbd the merged bean definition the bean was created with
     * @param pds the relevant property descriptors for the target bean
     * @param pvs the property values to be applied to the bean
     * @see #isExcludedFromDependencyCheck(java.beans.PropertyDescriptor)
     */
    protected void checkDependencies(
            String beanName, AbstractBeanDefinition mbd, PropertyDescriptor[] pds, PropertyValues pvs)
            throws UnsatisfiedDependencyException {

        int dependencyCheck = mbd.getDependencyCheck();
        for (PropertyDescriptor pd : pds) {
            if (pd.getWriteMethod() != null && !pvs.contains(pd.getName())) {
                boolean isSimple = BeanUtils.isSimpleProperty(pd.getPropertyType());
                boolean unsatisfied = (dependencyCheck == RootBeanDefinition.DEPENDENCY_CHECK_ALL) ||
                        (isSimple && dependencyCheck == RootBeanDefinition.DEPENDENCY_CHECK_SIMPLE) ||
                        (!isSimple && dependencyCheck == RootBeanDefinition.DEPENDENCY_CHECK_OBJECTS);
                if (unsatisfied) {
                    throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, pd.getName(),
                            "Set this property value or disable dependency checking for this bean.");
                }
            }
        }
    }

    /**
     * Apply the given property values, resolving any runtime references
     * to other beans in this bean factory. Must use deep copy, so we
     * don't permanently modify this property.
     * @param beanName the bean name passed for better exception information
     * @param mbd the merged bean definition
     * @param bw the BeanWrapper wrapping the target object
     * @param pvs the new property values
     */
    protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
        if (pvs == null || pvs.isEmpty()) {
            return;
        }

        MutablePropertyValues mpvs = null;
        List<PropertyValue> original;

        if (System.getSecurityManager() != null) {
            if (bw instanceof BeanWrapperImpl) {
                ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
            }
        }

        if (pvs instanceof MutablePropertyValues) {
            mpvs = (MutablePropertyValues) pvs;
            if (mpvs.isConverted()) {
                // Shortcut: use the pre-converted values as-is.
                try {
                    bw.setPropertyValues(mpvs);
                    return;
                }
                catch (BeansException ex) {
                    throw new BeanCreationException(
                            mbd.getResourceDescription(), beanName, "Error setting property values", ex);
                }
            }
            original = mpvs.getPropertyValueList();
        }
        else {
            original = Arrays.asList(pvs.getPropertyValues());
        }

        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
            converter = bw;
        }
        BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

        // Create a deep copy, resolving any references for values.
        List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
        boolean resolveNecessary = false;
        for (PropertyValue pv : original) {
            if (pv.isConverted()) {
                deepCopy.add(pv);
            }
            else {
                String propertyName = pv.getName();
                Object originalValue = pv.getValue();
                Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
                Object convertedValue = resolvedValue;
                boolean convertible = bw.isWritableProperty(propertyName) &&
                        !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
                if (convertible) {
                    convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
                }
                // Possibly store converted value in merged bean definition,
                // in order to avoid re-conversion for every created bean instance.
                if (resolvedValue == originalValue) {
                    if (convertible) {
                        pv.setConvertedValue(convertedValue);
                    }
                    deepCopy.add(pv);
                }
                else if (convertible && originalValue instanceof TypedStringValue &&
                        !((TypedStringValue) originalValue).isDynamic() &&
                        !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
                    pv.setConvertedValue(convertedValue);
                    deepCopy.add(pv);
                }
                else {
                    resolveNecessary = true;
                    deepCopy.add(new PropertyValue(pv, convertedValue));
                }
            }
        }
        if (mpvs != null && !resolveNecessary) {
            mpvs.setConverted();
        }

        // Set our (possibly massaged) deep copy.
        try {
            bw.setPropertyValues(new MutablePropertyValues(deepCopy));
        }
        catch (BeansException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Error setting property values", ex);
        }
    }

    /**
     * Convert the given value for the specified target property.
     */
    private Object convertForProperty(Object value, String propertyName, BeanWrapper bw, TypeConverter converter) {
        if (converter instanceof BeanWrapperImpl) {
            return ((BeanWrapperImpl) converter).convertForProperty(value, propertyName);
        }
        else {
            PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
            MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
            return converter.convertIfNecessary(value, pd.getPropertyType(), methodParam);
        }
    }


    /**
     * Initialize the given bean instance, applying factory callbacks
     * as well as init methods and bean post processors.
     * <p>Called from {@link #createBean} for traditionally defined beans,
     * and from {@link #initializeBean} for existing bean instances.
     * @param beanName the bean name in the factory (for debugging purposes)
     * @param bean the new bean instance we may need to initialize
     * @param mbd the bean definition that the bean was created with
     * (can also be {@code null}, if given an existing bean instance)
     * @return the initialized bean instance (potentially wrapped)
     * @see BeanNameAware
     * @see BeanClassLoaderAware
     * @see BeanFactoryAware
     * @see #applyBeanPostProcessorsBeforeInitialization
     * @see #invokeInitMethods
     * @see #applyBeanPostProcessorsAfterInitialization
     */
    protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, getAccessControlContext());
        }
        else {
            invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }

        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

    private void invokeAwareMethods(final String beanName, final Object bean) {
        if (bean instanceof Aware) {
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
            }
        }
    }

    /**
     * Give a bean a chance to react now all its properties are set,
     * and a chance to know about its owning bean factory (this object).
     * This means checking whether the bean implements InitializingBean or defines
     * a custom init method, and invoking the necessary callback(s) if it does.
     * @param beanName the bean name in the factory (for debugging purposes)
     * @param bean the new bean instance we may need to initialize
     * @param mbd the merged bean definition that the bean was created with
     * (can also be {@code null}, if given an existing bean instance)
     * @throws Throwable if thrown by init methods or by the invocation process
     * @see #invokeCustomInitMethod
     */
    protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
            throws Throwable {

        boolean isInitializingBean = (bean instanceof InitializingBean);
        if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
            if (logger.isDebugEnabled()) {
                logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
            }
            if (System.getSecurityManager() != null) {
                try {
                    AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                        @Override
                        public Object run() throws Exception {
                            ((InitializingBean) bean).afterPropertiesSet();
                            return null;
                        }
                    }, getAccessControlContext());
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
                ((InitializingBean) bean).afterPropertiesSet();
            }
        }

        if (mbd != null) {
            String initMethodName = mbd.getInitMethodName();
            if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                    !mbd.isExternallyManagedInitMethod(initMethodName)) {
                invokeCustomInitMethod(beanName, bean, mbd);
            }
        }
    }

    /**
     * Invoke the specified custom init method on the given bean.
     * Called by invokeInitMethods.
     * <p>Can be overridden in subclasses for custom resolution of init
     * methods with arguments.
     * @see #invokeInitMethods
     */
    protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd)
            throws Throwable {

        String initMethodName = mbd.getInitMethodName();
        final Method initMethod = (mbd.isNonPublicAccessAllowed() ?
                BeanUtils.findMethod(bean.getClass(), initMethodName) :
                ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
        if (initMethod == null) {
            if (mbd.isEnforceInitMethod()) {
                throw new BeanDefinitionValidationException("Couldn't find an init method named '" +
                        initMethodName + "' on bean with name '" + beanName + "'");
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("No default init method named '" + initMethodName +
                            "' found on bean with name '" + beanName + "'");
                }
                // Ignore non-existent default lifecycle methods.
                return;
            }
        }

        if (logger.isDebugEnabled()) {
            logger.debug("Invoking init method  '" + initMethodName + "' on bean with name '" + beanName + "'");
        }

        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                @Override
                public Object run() throws Exception {
                    ReflectionUtils.makeAccessible(initMethod);
                    return null;
                }
            });
            try {
                AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                    @Override
                    public Object run() throws Exception {
                        initMethod.invoke(bean);
                        return null;
                    }
                }, getAccessControlContext());
            }
            catch (PrivilegedActionException pae) {
                InvocationTargetException ex = (InvocationTargetException) pae.getException();
                throw ex.getTargetException();
            }
        }
        else {
            try {
                ReflectionUtils.makeAccessible(initMethod);
                initMethod.invoke(bean);
            }
            catch (InvocationTargetException ex) {
                throw ex.getTargetException();
            }
        }
    }


    /**
     * Applies the {@code postProcessAfterInitialization} callback of all
     * registered BeanPostProcessors, giving them a chance to post-process the
     * object obtained from FactoryBeans (for example, to auto-proxy them).
     * @see #applyBeanPostProcessorsAfterInitialization
     */
    @Override
    protected Object postProcessObjectFromFactoryBean(Object object, String beanName) {
        return applyBeanPostProcessorsAfterInitialization(object, beanName);
    }

    /**
     * Overridden to clear FactoryBean instance cache as well.
     */
    @Override
    protected void removeSingleton(String beanName) {
        super.removeSingleton(beanName);
        this.factoryBeanInstanceCache.remove(beanName);
    }


    /**
     * Special DependencyDescriptor variant for Spring's good old autowire="byType" mode.
     * Always optional; never considering the parameter name for choosing a primary candidate.
     */
    @SuppressWarnings("serial")
    private static class AutowireByTypeDependencyDescriptor extends DependencyDescriptor {

        public AutowireByTypeDependencyDescriptor(MethodParameter methodParameter, boolean eager) {
            super(methodParameter, false, eager);
        }

        @Override
        public String getDependencyName() {
            return null;
        }
    }

}

（4.2）AbstractAutowireCapableBeanFactory 类中 createBean 方法

/**
     * Central method of this class: creates a bean instance,
     * populates the bean instance, applies post-processors, etc.
     * @see #doCreateBean
     */
    @Override
    protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        RootBeanDefinition mbdToUse = mbd;

        // Make sure bean class is actually resolved at this point, and
        // clone the bean definition in case of a dynamically resolved Class
        // which cannot be stored in the shared merged bean definition.
        //锁定class,根据设置的class属性或者根据className来解析class
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            //给BeanPostProcessors一个机会来返回代理来替代真正的实例
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

 （4.3）AbstractAutowireCapableBeanFactory 类中 resolveBeforeInstantiation 方法

/**
     * Apply before-instantiation post-processors, resolving whether there is a
     * before-instantiation shortcut for the specified bean.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return the shortcut-determined bean instance, or {@code null} if none
     */
    protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
        Object bean = null;
        if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
            // Make sure bean class is actually resolved at this point.
            if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
                Class<?> targetType = determineTargetType(beanName, mbd);
                if (targetType != null) {
                    bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                    if (bean != null) {
                        bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                    }
                }
            }
            mbd.beforeInstantiationResolved = (bean != null);
        }
        return bean;
    }

 

五：创建bean

    在上一小节中，当经历过resolveBeforeInstantiation方法后，程序有两个选择，如果创建了代理或者重写了InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法，并在方法postProcessBeforeInstantiation中改变了bean，则直接返回就可以了，否则需要进行常规bean的创建。而常规bean的创建就是在doCreateBean中完成的。

（5.1）AbstractAutowireCapableBeanFactory 类中doCreateBean方法

/**
     * Actually create the specified bean. Pre-creation processing has already happened
     * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
     * <p>Differentiates between default bean instantiation, use of a
     * factory method, and autowiring a constructor.
     * @param beanName the name of the bean
     * @param mbd the merged bean definition for the bean
     * @param args explicit arguments to use for constructor or factory method invocation
     * @return a new instance of the bean
     * @throws BeanCreationException if the bean could not be created
     * @see #instantiateBean
     * @see #instantiateUsingFactoryMethod
     * @see #autowireConstructor
     */
    protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            //根据指定bean使用对应的策略创建新的实例，如：工厂方法，构造函数自动注入，简单初始化
　　　　　　　instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
        mbd.resolvedTargetType = beanType;

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                try {
                    applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "Post-processing of merged bean definition failed", ex);
                }
                mbd.postProcessed = true;
            }
        }

        // Eagerly cache singletons to be able to resolve circular references
        // even when triggered by lifecycle interfaces like BeanFactoryAware.
        boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
                isSingletonCurrentlyInCreation(beanName));
        if (earlySingletonExposure) {
            if (logger.isDebugEnabled()) {
                logger.debug("Eagerly caching bean '" + beanName +
                        "' to allow for resolving potential circular references");
            }
            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
            //对bean进行填充，将各个属性值注入，其中，可能存在依赖于其他bean的属性，则会递归初始化依赖bean
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }

        if (earlySingletonExposure) {
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
                    for (String dependentBean : dependentBeans) {
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name '" + beanName + "' has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        try {
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

函数概要思路：

1. 如果是单例则需要首先清除缓存。
2. 实例化bean，将BeanDefinition转换为BeanWrapper。转换是一个复杂的过程，但是我们可以尝试概括大致的功能，如下所示：

• 如果存在工厂方法则使用工厂方法进行初始化
• 一个类有多个构造函数，每个构造函数都有不同的参数，所以需要根据参数锁定构造函数并进行初始化。
• 如果既不存在工厂方法也不存在带有参数的构造函数，则使用默认的构造函数进行bean的实例化。

        3. MergedBeanDefinitionPostProcessor的应用。

            bean合并后的处理，Autowired注解正是通过此方法实现诸如类型的预解析。

 （5.2）创建bean的实例

（5.2.1）AbstractAutowireCapableBeanFactory 类中createBeanInstance方法

/**
     * Create a new instance for the specified bean, using an appropriate instantiation strategy:
     * factory method, constructor autowiring, or simple instantiation.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param args explicit arguments to use for constructor or factory method invocation
     * @return BeanWrapper for the new instance
     * @see #instantiateUsingFactoryMethod
     * @see #autowireConstructor
     * @see #instantiateBean
     */
    protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
        // Make sure bean class is actually resolved at this point.
        Class<?> beanClass = resolveBeanClass(mbd, beanName);

        if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
        }

        if (mbd.getFactoryMethodName() != null)  {
            return instantiateUsingFactoryMethod(beanName, mbd, args);
        }

        // Shortcut when re-creating the same bean...
        boolean resolved = false;
        boolean autowireNecessary = false;
        if (args == null) {
            synchronized (mbd.constructorArgumentLock) {
                if (mbd.resolvedConstructorOrFactoryMethod != null) {
                    resolved = true;
                    autowireNecessary = mbd.constructorArgumentsResolved;
                }
            }
        }
        if (resolved) {
            if (autowireNecessary) {
                //构造函数自动注入
                return autowireConstructor(beanName, mbd, null, null);
            }
            else {
                //使用默认构造函数构造
                return instantiateBean(beanName, mbd);
            }
        }

        // Need to determine the constructor...
        //需要根据参数解析构造函数
        Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
        if (ctors != null ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
                mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
            return autowireConstructor(beanName, mbd, ctors, args);
        }

        // No special handling: simply use no-arg constructor.
        return instantiateBean(beanName, mbd);
    }

分析：

1. 如果在RootBeanDefinition中存在factoryMethodName属性，或者说在配置文件中配置了factory-method，那么Spring会尝试使用instantiateUsingFactoryMethod(beanName, mbd, args)方法根据RootBeanDefinition中的配置生成bean的实例。
2. 解析构造函数并进行构造函数的实例化。因为一个bean对于的类中可能会有多个构造函数，而每个构造函数的参数不同，Spring在根据参数及类型去判断最终会使用哪个构造函数进行实例化。但是，判断的过程是个比较消耗性能的步骤，所以采用缓存机制，如果已经解析过则不需要重复解析而是直接从RootBeanDefinition中的属性resolvedConstructoOrFactoryMethod缓存的值去取，否则需要再次解析，并将解析的结果添加至RootBeanDefinition中的属性resolvedConstructorOrFactoryMethod中。

（5.2.2）autowireConstructor

    对于实例的创建Spring中分成了两种情况，一种是通用的实例化，另一种是带有参数的实例化。带有参数的实例化过程相当复杂，因为存在着不确定性，所以在判断对应参数上做了大量工作。

（5.2.3）AbstractAutowireCapableBeanFactory 类中 instantiateBean

  不带参数的构造函数的实例化过程：

/**
     * Instantiate the given bean using its default constructor.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return BeanWrapper for the new instance
     */
    protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
        try {
            Object beanInstance;
            final BeanFactory parent = this;
            if (System.getSecurityManager() != null) {
                beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    @Override
                    public Object run() {
                        return getInstantiationStrategy().instantiate(mbd, beanName, parent);
                    }
                }, getAccessControlContext());
            }
            else {
                beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
            }
            BeanWrapper bw = new BeanWrapperImpl(beanInstance);
            initBeanWrapper(bw);
            return bw;
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
        }
    }

  此方法并没有什么实质性的逻辑，带有参数的实例构造中，Spring把精力都放在了构造函数以及参数的匹配上，所以如果没有参数的话那将是非常简单的一件事，直接调用实例化策略进行实例化就可以了。

（5.3）记录创建bean的ObjectFactory

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
        mbd.resolvedTargetType = beanType;

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                try {
                    applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "Post-processing of merged bean definition failed", ex);
                }
                mbd.postProcessed = true;
            }
        }

        // Eagerly cache singletons to be able to resolve circular references
        // even when triggered by lifecycle interfaces like BeanFactoryAware.
        boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
                isSingletonCurrentlyInCreation(beanName));
        if (earlySingletonExposure) {
            if (logger.isDebugEnabled()) {
                logger.debug("Eagerly caching bean '" + beanName +
                        "' to allow for resolving potential circular references");
            }
            //为避免后期循环依赖，可以在bean初始化完成前将创建实例的ObjectFactory加入工厂
            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }

        if (earlySingletonExposure) {
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
                    for (String dependentBean : dependentBeans) {
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name '" + beanName + "' has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        try {
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

• mbd.isSingleton()：此RootBeanDefinition代表的是否是单例。
• this.allowCircularReferences：是否允许循环依赖，并没有找到在配置文件中如何配置，但是在AbstractRefreshableApplicationContext中提供了设置函数，可以通过硬编码的方式进行设置或者可以通过自定义命名空间进行配置，其中硬编码的方式代码如下：ClassPathXmlApplicationContext bf = new ClassPathXmlApplicationContext("test.xml");    bf.setAllowBeanDefinitionOverriding(false);
• isSingletonCurrentlyInCreation(beanName)：该bean是否在创建中。在Spring中，会有个专门的属性默认为DefaultSingletonBeanRegistry的singletonsCurrentlyInCreation来记录bean的加载状态，在bean开始创建前会将beanName记录在属性中，在bean创建结束后将beanName从属性中移除。这个状态是在哪里记录的呢？不同scope的记录位置并不一样，我们以singleton为例，在singleton下记录属性的函数是在DefaultSingletonBeanRegistry类的public Object getSingleton(String beanName, ObjectFactory singletonFactory)函数的beforeSingletonCreation(beanName)和 aftersingletonCreation(beanName)中，在这两段函数中分别由 this.singletonsCurrentlyInCreation.add(beanName) 与 this.singletonsCurrentlyInCreation.remove(beanName)来进行状态的记录与移除。

    经过以上分析，我们了解变量earlySingletonExposure是否是单例，是否允许循环依赖，是否对应的bean正在创建的条件的综合。当着3个条件都满足时会执行addSingletonFactory操作，那么加入singletonFactory的作用是什么呢？又是在什么时候调用呢？

（5.3.1）DefaultSingletonBeanRegistry 类中的 addSingletonFactory 方法

public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {

/**
     * Add the given singleton factory for building the specified singleton
     * if necessary.
     * <p>To be called for eager registration of singletons, e.g. to be able to
     * resolve circular references.
     * @param beanName the name of the bean
     * @param singletonFactory the factory for the singleton object
     */
    protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(singletonFactory, "Singleton factory must not be null");
        synchronized (this.singletonObjects) {
            if (!this.singletonObjects.containsKey(beanName)) {
                this.singletonFactories.put(beanName, singletonFactory);
                this.earlySingletonObjects.remove(beanName);
                this.registeredSingletons.add(beanName);
            }
        }
    }


}

（5.3.2）AbstractAutowireCapableBeanFactory 类中 getEarlyBeanReference 方法

/**
     * Obtain a reference for early access to the specified bean,
     * typically for the purpose of resolving a circular reference.
     * @param beanName the name of the bean (for error handling purposes)
     * @param mbd the merged bean definition for the bean
     * @param bean the raw bean instance
     * @return the object to expose as bean reference
     */
    protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
        Object exposedObject = bean;
        if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                    SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
                    exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
                    if (exposedObject == null) {
                        return null;
                    }
                }
            }
        }
        return exposedObject;
    }

（5.4）属性注入

（5.4.1）AbstractAutowireCapableBeanFactory 类中 populateBean 方法

/**
     * Populate the bean instance in the given BeanWrapper with the property values
     * from the bean definition.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param bw BeanWrapper with bean instance
     */
    protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
        PropertyValues pvs = mbd.getPropertyValues();

        if (bw == null) {
            if (!pvs.isEmpty()) {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
            }
            else {
                // Skip property population phase for null instance.
                return;
            }
        }

        // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
        // state of the bean before properties are set. This can be used, for example,
        // to support styles of field injection.
        boolean continueWithPropertyPopulation = true;

        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                        continueWithPropertyPopulation = false;
                        break;
                    }
                }
            }
        }

        if (!continueWithPropertyPopulation) {
            return;
        }

        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

            // Add property values based on autowire by name if applicable.
            //根据名称自动注入
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
                autowireByName(beanName, mbd, bw, newPvs);
            }

            // Add property values based on autowire by type if applicable.
            //根据类型自动注入
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
                autowireByType(beanName, mbd, bw, newPvs);
            }

            pvs = newPvs;
        }

        boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
        boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

        if (hasInstAwareBpps || needsDepCheck) {
            PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
            if (hasInstAwareBpps) {
                for (BeanPostProcessor bp : getBeanPostProcessors()) {
                    if (bp instanceof InstantiationAwareBeanPostProcessor) {
                        InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                        //对所有需要依赖检查的属性进行后处理
                        pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                        if (pvs == null) {
                            return;
                        }
                    }
                }
            }
            if (needsDepCheck) {
                checkDependencies(beanName, mbd, filteredPds, pvs);
            }
        }

        //将属性运用到bean中
        applyPropertyValues(beanName, mbd, bw, pvs);
    }

在populateBean函数中提供了这样的处理流程。

1. InstantiationAwareBeanPostProcessor处理器的postProcessAfterInstantiation函数的应用，此函数可以控制程序是否继续进行属性填充。
2. 根据注入类型（byName/byType），提取依赖的bean，并统一存入PropertyValues中。
3. 应用InstantiationAwareBeanPostProcessor处理器的postProcessPropertyValues方法，对属性获取完毕填充前对属性的再次处理，典型应用是RequiredAnnotationBeanPostProcessor类中对属性的验证。
4. 将所有PropertyValues中的属性填充至BeanWrapper中。

    在上面的步骤中，我们感兴趣的分别是依赖注入（autowiredByName/autowiredByTpye）以及属性填充。

（5.4.2）AbstractAutowireCapableBeanFactory 类中 autowireByName

/**
     * Fill in any missing property values with references to
     * other beans in this factory if autowire is set to "byName".
     * @param beanName the name of the bean we're wiring up.
     * Useful for debugging messages; not used functionally.
     * @param mbd bean definition to update through autowiring
     * @param bw BeanWrapper from which we can obtain information about the bean
     * @param pvs the PropertyValues to register wired objects with
     */
    protected void autowireByName(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
            if (containsBean(propertyName)) {
                Object bean = getBean(propertyName);
                pvs.add(propertyName, bean);
                registerDependentBean(propertyName, beanName);
                if (logger.isDebugEnabled()) {
                    logger.debug("Added autowiring by name from bean name '" + beanName +
                            "' via property '" + propertyName + "' to bean named '" + propertyName + "'");
                }
            }
            else {
                if (logger.isTraceEnabled()) {
                    logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
                            "' by name: no matching bean found");
                }
            }
        }
    }

    在传入的参数pvs中找出已经加载的bean，并递归实例化，进而加入到pvs中。

（5.4.3）AbstractAutowireCapableBeanFactory 类中 autowireByType

/**
     * Abstract method defining "autowire by type" (bean properties by type) behavior.
     * <p>This is like PicoContainer default, in which there must be exactly one bean
     * of the property type in the bean factory. This makes bean factories simple to
     * configure for small namespaces, but doesn't work as well as standard Spring
     * behavior for bigger applications.
     * @param beanName the name of the bean to autowire by type
     * @param mbd the merged bean definition to update through autowiring
     * @param bw BeanWrapper from which we can obtain information about the bean
     * @param pvs the PropertyValues to register wired objects with
     */
    protected void autowireByType(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
            converter = bw;
        }

        Set<String> autowiredBeanNames = new LinkedHashSet<String>(4);
        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
            try {
                PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
                // Don't try autowiring by type for type Object: never makes sense,
                // even if it technically is a unsatisfied, non-simple property.
                if (Object.class != pd.getPropertyType()) {
                    MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
                    // Do not allow eager init for type matching in case of a prioritized post-processor.
                    boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());
                    DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
                    Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
                    if (autowiredArgument != null) {
                        pvs.add(propertyName, autowiredArgument);
                    }
                    for (String autowiredBeanName : autowiredBeanNames) {
                        registerDependentBean(autowiredBeanName, beanName);
                        if (logger.isDebugEnabled()) {
                            logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" +
                                    propertyName + "' to bean named '" + autowiredBeanName + "'");
                        }
                    }
                    autowiredBeanNames.clear();
                }
            }
            catch (BeansException ex) {
                throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
            }
        }
    }

  DefaultListableBeanFactory类中 resolveDependency 方法

@Override
    public Object resolveDependency(DependencyDescriptor descriptor, String requestingBeanName,
            Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {

        descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
        if (javaUtilOptionalClass == descriptor.getDependencyType()) {
            return new OptionalDependencyFactory().createOptionalDependency(descriptor, requestingBeanName);
        }
        else if (ObjectFactory.class == descriptor.getDependencyType() ||
                ObjectProvider.class == descriptor.getDependencyType()) {
            return new DependencyObjectProvider(descriptor, requestingBeanName);
        }
        else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
            return new Jsr330ProviderFactory().createDependencyProvider(descriptor, requestingBeanName);
        }
        else {
            Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
                    descriptor, requestingBeanName);
            if (result == null) {
                result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
            }
            return result;
        }
    }

    public Object doResolveDependency(DependencyDescriptor descriptor, String beanName,
            Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {

        InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
        try {
            Object shortcut = descriptor.resolveShortcut(this);
            if (shortcut != null) {
                return shortcut;
            }

            Class<?> type = descriptor.getDependencyType();
            /**
            * 用于支持Spring中新增的注解@Value
            */
            Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
            if (value != null) {
                if (value instanceof String) {
                    String strVal = resolveEmbeddedValue((String) value);
                    BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
                    value = evaluateBeanDefinitionString(strVal, bd);
                }
                TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
                return (descriptor.getField() != null ?
                        converter.convertIfNecessary(value, type, descriptor.getField()) :
                        converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
            }

            Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
            if (multipleBeans != null) {
                return multipleBeans;
            }

            //根据属性类型找到beanFactory中所有类型的匹配bean
            //返回值的构成为：key==匹配的beanName，value=beanName对应的实例化后的bean（通过getBean(beanName）返回）
            Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
            if (matchingBeans.isEmpty()) {
                //如果autowire的require属性为true二找到的匹配项却为空则只能抛出异常
                if (descriptor.isRequired()) {
                    raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
                }
                return null;
            }

            String autowiredBeanName;
            Object instanceCandidate;

            if (matchingBeans.size() > 1) {
                autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
                if (autowiredBeanName == null) {
                    if (descriptor.isRequired() || !indicatesMultipleBeans(type)) {
                        return descriptor.resolveNotUnique(type, matchingBeans);
                    }
                    else {
                        // In case of an optional Collection/Map, silently ignore a non-unique case:
                        // possibly it was meant to be an empty collection of multiple regular beans
                        // (before 4.3 in particular when we didn't even look for collection beans).
                        return null;
                    }
                }
                instanceCandidate = matchingBeans.get(autowiredBeanName);
            }
            else {
                // We have exactly one match.
                Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
                autowiredBeanName = entry.getKey();
                instanceCandidate = entry.getValue();
            }

            if (autowiredBeanNames != null) {
                autowiredBeanNames.add(autowiredBeanName);
            }
            return (instanceCandidate instanceof Class ?
                    descriptor.resolveCandidate(autowiredBeanName, type, this) : instanceCandidate);
        }
        finally {
            ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
        }
    }

    寻找类型的匹配执行顺序时，首先尝试使用解析器进行解析，如果解析器没有成功解析，那么可能是使用默认的解析器没有做任何处理，或者使用了自定义的解析器。

（5.4.4）applyPropertyValues

    程序运行到这里，已经完成了对所有注入属性的获取，但是获取的属性是以PropertyValues形式存在的，还并没有应用到已经实例化的bean中，这一工作是在applyPropertyValues中。

  AbstractAutowireCapableBeanFactory 类中 applyPropertyValues

/**
     * Apply the given property values, resolving any runtime references
     * to other beans in this bean factory. Must use deep copy, so we
     * don't permanently modify this property.
     * @param beanName the bean name passed for better exception information
     * @param mbd the merged bean definition
     * @param bw the BeanWrapper wrapping the target object
     * @param pvs the new property values
     */
    protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
        if (pvs == null || pvs.isEmpty()) {
            return;
        }

        MutablePropertyValues mpvs = null;
        List<PropertyValue> original;

        if (System.getSecurityManager() != null) {
            if (bw instanceof BeanWrapperImpl) {
                ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
            }
        }

        if (pvs instanceof MutablePropertyValues) {
            mpvs = (MutablePropertyValues) pvs;
            //如果mpvs中的值已经被转换为对应的类型那么可以直接设置到beanwapper中
            if (mpvs.isConverted()) {
                // Shortcut: use the pre-converted values as-is.
                try {
                    bw.setPropertyValues(mpvs);
                    return;
                }
                catch (BeansException ex) {
                    throw new BeanCreationException(
                            mbd.getResourceDescription(), beanName, "Error setting property values", ex);
                }
            }
            original = mpvs.getPropertyValueList();
        }
        else {
            //如果pvs并不是使用MutablePropertyValues封装的类型，那么直接使用原始的属性封装方法
            original = Arrays.asList(pvs.getPropertyValues());
        }

        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
            converter = bw;
        }
        //获取对应的解析器
        BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

        // Create a deep copy, resolving any references for values.
        List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
        boolean resolveNecessary = false;
        //遍历属性，将属性转换为对应类的对应属性的类型
        for (PropertyValue pv : original) {
            if (pv.isConverted()) {
                deepCopy.add(pv);
            }
            else {
                String propertyName = pv.getName();
                Object originalValue = pv.getValue();
                Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
                Object convertedValue = resolvedValue;
                boolean convertible = bw.isWritableProperty(propertyName) &&
                        !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
                if (convertible) {
                    convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
                }
                // Possibly store converted value in merged bean definition,
                // in order to avoid re-conversion for every created bean instance.
                if (resolvedValue == originalValue) {
                    if (convertible) {
                        pv.setConvertedValue(convertedValue);
                    }
                    deepCopy.add(pv);
                }
                else if (convertible && originalValue instanceof TypedStringValue &&
                        !((TypedStringValue) originalValue).isDynamic() &&
                        !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
                    pv.setConvertedValue(convertedValue);
                    deepCopy.add(pv);
                }
                else {
                    resolveNecessary = true;
                    deepCopy.add(new PropertyValue(pv, convertedValue));
                }
            }
        }
        if (mpvs != null && !resolveNecessary) {
            mpvs.setConverted();
        }

        // Set our (possibly massaged) deep copy.
        try {
            bw.setPropertyValues(new MutablePropertyValues(deepCopy));
        }
        catch (BeansException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Error setting property values", ex);
        }
    }

（5.5）初始化bean

/**
     * Initialize the given bean instance, applying factory callbacks
     * as well as init methods and bean post processors.
     * <p>Called from {@link #createBean} for traditionally defined beans,
     * and from {@link #initializeBean} for existing bean instances.
     * @param beanName the bean name in the factory (for debugging purposes)
     * @param bean the new bean instance we may need to initialize
     * @param mbd the bean definition that the bean was created with
     * (can also be {@code null}, if given an existing bean instance)
     * @return the initialized bean instance (potentially wrapped)
     * @see BeanNameAware
     * @see BeanClassLoaderAware
     * @see BeanFactoryAware
     * @see #applyBeanPostProcessorsBeforeInitialization
     * @see #invokeInitMethods
     * @see #applyBeanPostProcessorsAfterInitialization
     */
    protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, getAccessControlContext());
        }
        else {
            invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }

        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

    private void invokeAwareMethods(final String beanName, final Object bean) {
        if (bean instanceof Aware) {
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
            }
        }
    }

    /**
     * Give a bean a chance to react now all its properties are set,
     * and a chance to know about its owning bean factory (this object).
     * This means checking whether the bean implements InitializingBean or defines
     * a custom init method, and invoking the necessary callback(s) if it does.
     * @param beanName the bean name in the factory (for debugging purposes)
     * @param bean the new bean instance we may need to initialize
     * @param mbd the merged bean definition that the bean was created with
     * (can also be {@code null}, if given an existing bean instance)
     * @throws Throwable if thrown by init methods or by the invocation process
     * @see #invokeCustomInitMethod
     */
    protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
            throws Throwable {

        boolean isInitializingBean = (bean instanceof InitializingBean);
        if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
            if (logger.isDebugEnabled()) {
                logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
            }
            if (System.getSecurityManager() != null) {
                try {
                    AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                        @Override
                        public Object run() throws Exception {
                            ((InitializingBean) bean).afterPropertiesSet();
                            return null;
                        }
                    }, getAccessControlContext());
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
                ((InitializingBean) bean).afterPropertiesSet();
            }
        }

        if (mbd != null) {
            String initMethodName = mbd.getInitMethodName();
            if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                    !mbd.isExternallyManagedInitMethod(initMethodName)) {
                invokeCustomInitMethod(beanName, bean, mbd);
            }
        }
    }

    /**
     * Invoke the specified custom init method on the given bean.
     * Called by invokeInitMethods.
     * <p>Can be overridden in subclasses for custom resolution of init
     * methods with arguments.
     * @see #invokeInitMethods
     */
    protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd)
            throws Throwable {

        String initMethodName = mbd.getInitMethodName();
        final Method initMethod = (mbd.isNonPublicAccessAllowed() ?
                BeanUtils.findMethod(bean.getClass(), initMethodName) :
                ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
        if (initMethod == null) {
            if (mbd.isEnforceInitMethod()) {
                throw new BeanDefinitionValidationException("Couldn't find an init method named '" +
                        initMethodName + "' on bean with name '" + beanName + "'");
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("No default init method named '" + initMethodName +
                            "' found on bean with name '" + beanName + "'");
                }
                // Ignore non-existent default lifecycle methods.
                return;
            }
        }

        if (logger.isDebugEnabled()) {
            logger.debug("Invoking init method  '" + initMethodName + "' on bean with name '" + beanName + "'");
        }

        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                @Override
                public Object run() throws Exception {
                    ReflectionUtils.makeAccessible(initMethod);
                    return null;
                }
            });
            try {
                AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                    @Override
                    public Object run() throws Exception {
                        initMethod.invoke(bean);
                        return null;
                    }
                }, getAccessControlContext());
            }
            catch (PrivilegedActionException pae) {
                InvocationTargetException ex = (InvocationTargetException) pae.getException();
                throw ex.getTargetException();
            }
        }
        else {
            try {
                ReflectionUtils.makeAccessible(initMethod);
                initMethod.invoke(bean);
            }
            catch (InvocationTargetException ex) {
                throw ex.getTargetException();
            }
        }
    }

1. 激活Aware方法

              Spring中提供了一下Aware相关接口，比如BeanFactoryAware，ApplicationContextAware，ResourceLoaderAware，ServletContextAware等，实现这些Aware接口的bean在被初始化之后，可以取得一些相对应的资源，例如实现BeanFactoryAware的bean在初始后，Spring容器将会注入BeanFactory的实例，而实现ApplicationContextAware的bean，在bean被初始后，将会被注入ApplicationContext的实例等。

  示例：

    

  2. 处理器的应用

@Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            result = beanProcessor.postProcessBeforeInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

  3. 激活自定义的init方法

    客户定制的初始化方法除了我们熟知的使用配置init-method外，还有使自定义的bean实现InitializingBean接口，并在afterPropertiesSet中实现自己的初始化业务逻辑。

    init-method与afterPropertiesSet都是在初始化bean时执行，执行顺序是afterPropertiesSet先执行，而init-method后执行。

（5.6）注册DisposableBean

    Spring中不但提供了对应初始化方法的扩展入口，同样也提供了销毁方法的扩展入口，对应销毁方法的扩展，除了我们熟知的配置属性destory-method方法外，用户还可以注册后处理器DestructionAwareBeanPostProcessor来统一处理bean的销毁方法，代码如下：

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
     /**
     * Add the given bean to the list of disposable beans in this factory,
     * registering its DisposableBean interface and/or the given destroy method
     * to be called on factory shutdown (if applicable). Only applies to singletons.
     * @param beanName the name of the bean
     * @param bean the bean instance
     * @param mbd the bean definition for the bean
     * @see RootBeanDefinition#isSingleton
     * @see RootBeanDefinition#getDependsOn
     * @see #registerDisposableBean
     * @see #registerDependentBean
     */
    protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
        AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
        if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
            if (mbd.isSingleton()) {
                // Register a DisposableBean implementation that performs all destruction
                // work for the given bean: DestructionAwareBeanPostProcessors,
                // DisposableBean interface, custom destroy method.
                registerDisposableBean(beanName,
                        new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
            }
            else {
                // A bean with a custom scope...
                Scope scope = this.scopes.get(mbd.getScope());
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
                }
                scope.registerDestructionCallback(beanName,
                        new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
            }
        }
    }

}