• 【Spring源码分析】非懒加载的单例Bean初始化过程(下篇)


    doCreateBean方法

    上文【Spring源码分析】非懒加载的单例Bean初始化过程(上篇),分析了单例的Bean初始化流程,并跟踪代码进入了主流程,看到了Bean是如何被实例化出来的。先贴一下AbstractAutowireCapableBeanFactory的doCreateBean方法代码:

     1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
     2     // Instantiate the bean.
     3     BeanWrapper instanceWrapper = null;
     4     if (mbd.isSingleton()) {
     5         instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
     6     }
     7     if (instanceWrapper == null) {
     8         instanceWrapper = createBeanInstance(beanName, mbd, args);
     9     }
    10     final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
    11     Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
    12 
    13     // Allow post-processors to modify the merged bean definition.
    14     synchronized (mbd.postProcessingLock) {
    15         if (!mbd.postProcessed) {
    16             applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
    17             mbd.postProcessed = true;
    18         }
    19     }
    20 
    21     // Eagerly cache singletons to be able to resolve circular references
    22     // even when triggered by lifecycle interfaces like BeanFactoryAware.
    23     boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
    24             isSingletonCurrentlyInCreation(beanName));
    25     if (earlySingletonExposure) {
    26         if (logger.isDebugEnabled()) {
    27             logger.debug("Eagerly caching bean '" + beanName +
    28                     "' to allow for resolving potential circular references");
    29         }
    30         addSingletonFactory(beanName, new ObjectFactory() {
    31             public Object getObject() throws BeansException {
    32                 return getEarlyBeanReference(beanName, mbd, bean);
    33             }
    34         });
    35     }
    36 
    37     // Initialize the bean instance.
    38     Object exposedObject = bean;
    39     try {
    40         populateBean(beanName, mbd, instanceWrapper);
    41         if (exposedObject != null) {
    42             exposedObject = initializeBean(beanName, exposedObject, mbd);
    43         }
    44     }
    45     catch (Throwable ex) {
    46         if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
    47             throw (BeanCreationException) ex;
    48         }
    49         else {
    50             throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
    51         }
    52     }
    53 
    54     if (earlySingletonExposure) {
    55         Object earlySingletonReference = getSingleton(beanName, false);
    56         if (earlySingletonReference != null) {
    57             if (exposedObject == bean) {
    58                 exposedObject = earlySingletonReference;
    59             }
    60             else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
    61                 String[] dependentBeans = getDependentBeans(beanName);
    62                 Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
    63                 for (String dependentBean : dependentBeans) {
    64                     if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
    65                         actualDependentBeans.add(dependentBean);
    66                     }
    67                 }
    68                 if (!actualDependentBeans.isEmpty()) {
    69                     throw new BeanCurrentlyInCreationException(beanName,
    70                             "Bean with name '" + beanName + "' has been injected into other beans [" +
    71                             StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
    72                             "] in its raw version as part of a circular reference, but has eventually been " +
    73                             "wrapped. This means that said other beans do not use the final version of the " +
    74                             "bean. This is often the result of over-eager type matching - consider using " +
    75                             "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
    76                 }
    77             }
    78         }
    79     }
    80 
    81     // Register bean as disposable.
    82     try {
    83         registerDisposableBeanIfNecessary(beanName, bean, mbd);
    84     }
    85     catch (BeanDefinitionValidationException ex) {
    86         throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
    87     }
    88 
    89     return exposedObject;
    90 }

    下面继续分析初始化一个Bean的流程,不太重要的流程就跳过了。

    属性注入

    属性注入的代码比较好找,可以看一下40行,取名为populateBean,即填充Bean的意思,看一下代码实现:

     1 protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) {
     2     PropertyValues pvs = mbd.getPropertyValues();
     3 
     4     if (bw == null) {
     5         if (!pvs.isEmpty()) {
     6             throw new BeanCreationException(
     7                     mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
     8         }
     9         else {
    10             // Skip property population phase for null instance.
    11             return;
    12         }
    13     }
    14 
    15     // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
    16     // state of the bean before properties are set. This can be used, for example,
    17     // to support styles of field injection.
    18     boolean continueWithPropertyPopulation = true;
    19 
    20     if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
    21         for (BeanPostProcessor bp : getBeanPostProcessors()) {
    22             if (bp instanceof InstantiationAwareBeanPostProcessor) {
    23                 InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
    24                 if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
    25                     continueWithPropertyPopulation = false;
    26                     break;
    27                 }
    28             }
    29         }
    30     }
    31 
    32     if (!continueWithPropertyPopulation) {
    33         return;
    34     }
    35 
    36     if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
    37             mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    38         MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
    39 
    40         // Add property values based on autowire by name if applicable.
    41         if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
    42             autowireByName(beanName, mbd, bw, newPvs);
    43         }
    44 
    45         // Add property values based on autowire by type if applicable.
    46         if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    47             autowireByType(beanName, mbd, bw, newPvs);
    48         }
    49 
    50         pvs = newPvs;
    51     }
    52 
    53     boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
    54     boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
    55 
    56     if (hasInstAwareBpps || needsDepCheck) {
    57         PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
    58         if (hasInstAwareBpps) {
    59             for (BeanPostProcessor bp : getBeanPostProcessors()) {
    60                 if (bp instanceof InstantiationAwareBeanPostProcessor) {
    61                     InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
    62                     pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
    63                     if (pvs == null) {
    64                         return;
    65                     }
    66                 }
    67             }
    68         }
    69         if (needsDepCheck) {
    70             checkDependencies(beanName, mbd, filteredPds, pvs);
    71         }
    72     }
    73 
    74     applyPropertyValues(beanName, mbd, bw, pvs);
    75 }

    这段代码层次有点深,跟一下74行的applyPropertyValues方法,最后那个pvs的实现类为MutablePropertyValues,里面持有一个List<PropertyValue>,每一个PropertyValue包含了此Bean属性的属性名与属性值。74行的代码实现为:

     1 protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
     2     if (pvs == null || pvs.isEmpty()) {
     3         return;
     4     }
     5 
     6     MutablePropertyValues mpvs = null;
     7     List<PropertyValue> original;
     8         
     9     if (System.getSecurityManager()!= null) {
    10         if (bw instanceof BeanWrapperImpl) {
    11             ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
    12         }
    13     }
    14 
    15     if (pvs instanceof MutablePropertyValues) {
    16         mpvs = (MutablePropertyValues) pvs;
    17         if (mpvs.isConverted()) {
    18             // Shortcut: use the pre-converted values as-is.
    19             try {
    20                 bw.setPropertyValues(mpvs);
    21                 return;
    22             }
    23             catch (BeansException ex) {
    24                 throw new BeanCreationException(
    25                         mbd.getResourceDescription(), beanName, "Error setting property values", ex);
    26             }
    27         }
    28         original = mpvs.getPropertyValueList();
    29     }
    30     else {
    31         original = Arrays.asList(pvs.getPropertyValues());
    32     }
    33 
    34     TypeConverter converter = getCustomTypeConverter();
    35     if (converter == null) {
    36         converter = bw;
    37     }
    38     BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
    39 
    40     // Create a deep copy, resolving any references for values.
    41     List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
    42     boolean resolveNecessary = false;
    43     for (PropertyValue pv : original) {
    44         if (pv.isConverted()) {
    45             deepCopy.add(pv);
    46         }
    47         else {
    48             String propertyName = pv.getName();
    49             Object originalValue = pv.getValue();
    50             Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
    51             Object convertedValue = resolvedValue;
    52             boolean convertible = bw.isWritableProperty(propertyName) &&
    53                         !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
    54             if (convertible) {
    55                 convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
    56             }
    57             // Possibly store converted value in merged bean definition,
    58             // in order to avoid re-conversion for every created bean instance.
    59             if (resolvedValue == originalValue) {
    60                 if (convertible) {
    61                     pv.setConvertedValue(convertedValue);
    62                 }
    63                 deepCopy.add(pv);
    64             }
    65             else if (convertible && originalValue instanceof TypedStringValue &&
    66                     !((TypedStringValue) originalValue).isDynamic() &&
    67                     !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
    68                 pv.setConvertedValue(convertedValue);
    69                 deepCopy.add(pv);
    70             }
    71             else {
    72                 resolveNecessary = true;
    73                 deepCopy.add(new PropertyValue(pv, convertedValue));
    74             }
    75         }
    76     }
    77     if (mpvs != null && !resolveNecessary) {
    78         mpvs.setConverted();
    79     }
    80 
    81     // Set our (possibly massaged) deep copy.
    82     try {
    83         bw.setPropertyValues(new MutablePropertyValues(deepCopy));
    84     }
    85     catch (BeansException ex) {
    86         throw new BeanCreationException(
    87                 mbd.getResourceDescription(), beanName, "Error setting property values", ex);
    88     }
    89 }

    之后在第41行~第76行做了一次深拷贝(只是名字叫做深拷贝而已,其实就是遍历PropertyValue然后一个一个赋值到一个新的List而不是Java语义上的Clone,这里使用深拷贝是为了解析Values值中的所有引用),将PropertyValue一个一个赋值到一个新的List里面去,起名为deepCopy。最后执行83行进行复制,bw即BeanWrapper,持有Bean实例的一个Bean包装类,看一下代码实现:

     1 public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
     2         throws BeansException {
     3 
     4     List<PropertyAccessException> propertyAccessExceptions = null;
     5     List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
     6             ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
     7     for (PropertyValue pv : propertyValues) {
     8         try {
     9             // This method may throw any BeansException, which won't be caught
    10             // here, if there is a critical failure such as no matching field.
    11             // We can attempt to deal only with less serious exceptions.
    12             setPropertyValue(pv);
    13         }
    14         catch (NotWritablePropertyException ex) {
    15             if (!ignoreUnknown) {
    16                 throw ex;
    17             }
    18             // Otherwise, just ignore it and continue...
    19         }
    20         catch (NullValueInNestedPathException ex) {
    21             if (!ignoreInvalid) {
    22                 throw ex;
    23             }
    24             // Otherwise, just ignore it and continue...
    25         }
    26         catch (PropertyAccessException ex) {
    27             if (propertyAccessExceptions == null) {
    28                 propertyAccessExceptions = new LinkedList<PropertyAccessException>();
    29             }
    30             propertyAccessExceptions.add(ex);
    31         }
    32     }
    33 
    34     // If we encountered individual exceptions, throw the composite exception.
    35     if (propertyAccessExceptions != null) {
    36         PropertyAccessException[] paeArray =
    37                 propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
    38         throw new PropertyBatchUpdateException(paeArray);
    39     }
    40 }

    这段代码没什么特别的,遍历前面的deepCopy,拿每一个PropertyValue,执行第12行的setPropertyValue:

     1 public void setPropertyValue(PropertyValue pv) throws BeansException {
     2     PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
     3     if (tokens == null) {
     4         String propertyName = pv.getName();
     5         BeanWrapperImpl nestedBw;
     6         try {
     7             nestedBw = getBeanWrapperForPropertyPath(propertyName);
     8         }
     9         catch (NotReadablePropertyException ex) {
    10             throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
    11                     "Nested property in path '" + propertyName + "' does not exist", ex);
    12         }
    13         tokens = getPropertyNameTokens(getFinalPath(nestedBw, propertyName));
    14         if (nestedBw == this) {
    15             pv.getOriginalPropertyValue().resolvedTokens = tokens;
    16         }
    17         nestedBw.setPropertyValue(tokens, pv);
    18     }
    19     else {
    20         setPropertyValue(tokens, pv);
    21     }
    22 }

    找一个合适的BeanWrapper,这里就是自身,然后执行17行的setPropertyValue方法进入最后一步,方法非常长,截取核心的一段:

     1 final Method writeMethod = (pd instanceof GenericTypeAwarePropertyDescriptor ?
     2     ((GenericTypeAwarePropertyDescriptor) pd).getWriteMethodForActualAccess() :
     3     pd.getWriteMethod());
     4     if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
     5     if (System.getSecurityManager()!= null) {
     6         AccessController.doPrivileged(new PrivilegedAction<Object>() {
     7                 public Object run() {
     8                     writeMethod.setAccessible(true);
     9                     return null;
    10                 }
    11             });
    12         }
    13         else {
    14             writeMethod.setAccessible(true);
    15         }
    16     }
    17     final Object value = valueToApply;
    18     if (System.getSecurityManager() != null) {
    19     try {
    20         AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
    21             public Object run() throws Exception {
    22                 writeMethod.invoke(object, value);
    23                 return null;
    24             }
    25         }, acc);
    26     }
    27     catch (PrivilegedActionException ex) {
    28         throw ex.getException();
    29     }
    30 }
    31 else {
    32     writeMethod.invoke(this.object, value);
    33 }                

    大致流程就是两步:

    (1)拿到写方法并将方法的可见性设置为true

    (2)拿到Value值,对Bean通过反射调用写方法

    这样完成了对于Bean属性值的设置。

    Aware注入

    接下来是Aware注入。在使用Spring的时候我们将自己的Bean实现BeanNameAware接口、BeanFactoryAware接口等,依赖容器帮我们注入当前Bean的名称或者Bean工厂,其代码实现先追溯到上面doCreateBean方法的42行initializeBean方法:

     1 protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
     2     if (System.getSecurityManager() != null) {
     3         AccessController.doPrivileged(new PrivilegedAction<Object>() {
     4             public Object run() {
     5                 invokeAwareMethods(beanName, bean);
     6                 return null;
     7             }
     8         }, getAccessControlContext());
     9     }
    10     else {
    11         invokeAwareMethods(beanName, bean);
    12     }
    13         
    14     Object wrappedBean = bean;
    15     if (mbd == null || !mbd.isSynthetic()) {
    16         wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    17     }
    18 
    19     try {
    20         invokeInitMethods(beanName, wrappedBean, mbd);
    21     }
    22     catch (Throwable ex) {
    23         throw new BeanCreationException(
    24                 (mbd != null ? mbd.getResourceDescription() : null),
    25                 beanName, "Invocation of init method failed", ex);
    26     }
    27 
    28     if (mbd == null || !mbd.isSynthetic()) {
    29         wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    30     }
    31     return wrappedBean;
    32 }

    看一下上面第5行的实现:

     1 private void invokeAwareMethods(final String beanName, final Object bean) {
     2     if (bean instanceof BeanNameAware) {
     3         ((BeanNameAware) bean).setBeanName(beanName);
     4     }
     5     if (bean instanceof BeanClassLoaderAware) {
     6         ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
     7     }
     8     if (bean instanceof BeanFactoryAware) {
     9         ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
    10     }
    11 }

    看到这里判断,如果bean是BeanNameAware接口的实现类会调用setBeanName方法、如果bean是BeanClassLoaderAware接口的实现类会调用setBeanClassLoader方法、如果是BeanFactoryAware接口的实现类会调用setBeanFactory方法,注入对应的属性值。

    调用BeanPostProcessor的postProcessBeforeInitialization方法

    上面initializeBean方法再看16行其实现:

     1 public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
     2         throws BeansException {
     3 
     4     Object result = existingBean;
     5     for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
     6         result = beanProcessor.postProcessBeforeInitialization(result, beanName);
     7         if (result == null) {
     8             return result;
     9         }
    10     }
    11     return result;
    12 }

    遍历每个BeanPostProcessor接口实现,调用postProcessBeforeInitialization方法,这个接口的调用时机之后会总结,这里就代码先简单提一下。

    调用初始化方法

    initializeBean方法的20行,调用Bean的初始化方法,看一下实现:

     1 protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
     2         throws Throwable {
     3 
     4     boolean isInitializingBean = (bean instanceof InitializingBean);
     5     if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
     6         if (logger.isDebugEnabled()) {
     7             logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
     8         }
     9         if (System.getSecurityManager() != null) {
    10             try {
    11                 AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
    12                     public Object run() throws Exception {
    13                         ((InitializingBean) bean).afterPropertiesSet();
    14                         return null;
    15                     }
    16                 }, getAccessControlContext());
    17             }
    18             catch (PrivilegedActionException pae) {
    19                 throw pae.getException();
    20             }
    21         }                
    22         else {
    23             ((InitializingBean) bean).afterPropertiesSet();
    24         }
    25     }
    26 
    27     if (mbd != null) {
    28         String initMethodName = mbd.getInitMethodName();
    29         if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
    30                     !mbd.isExternallyManagedInitMethod(initMethodName)) {
    31             invokeCustomInitMethod(beanName, bean, mbd);
    32         }
    33     }
    34 }

    看到,代码做了两件事情:

    1、先判断Bean是否InitializingBean的实现类,是的话,将Bean强转为InitializingBean,直接调用afterPropertiesSet()方法

    2、尝试去拿init-method,假如有的话,通过反射,调用initMethod

    因此,两种方法各有优劣:使用实现InitializingBean接口的方式效率更高一点,因为init-method方法是通过反射进行调用的;从另外一个角度讲,使用init-method方法之后和Spring的耦合度会更低一点。具体使用哪种方式调用初始化方法,看个人喜好。

    调用BeanPostProcessor的postProcessAfterInitialization方法

    最后一步,initializeBean方法的29行:

     1 public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
     2         throws BeansException {
     3 
     4     Object result = existingBean;
     5     for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
     6         result = beanProcessor.postProcessAfterInitialization(result, beanName);
     7         if (result == null) {
     8             return result;
     9         }
    10     }
    11     return result;
    12 }

    同样遍历BeanPostProcessor,调用postProcessAfterInitialization方法。因此对于BeanPostProcessor方法总结一下:

    1、在初始化每一个Bean的时候都会调用每一个配置的BeanPostProcessor的方法

    2、在Bean属性设置、Aware设置后调用postProcessBeforeInitialization方法

    3、在初始化方法调用后调用postProcessAfterInitialization方法

    注册需要执行销毁方法的Bean

    接下来看一下最上面doCreateBean方法的第83行registerDisposableBeanIfNecessary(beanName, bean, mbd)这一句,完成了创建Bean的最后一件事情:注册需要执行销毁方法的Bean。

    看一下方法的实现:

     1 protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
     2     AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
     3     if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
     4         if (mbd.isSingleton()) {
     5             // Register a DisposableBean implementation that performs all destruction
     6             // work for the given bean: DestructionAwareBeanPostProcessors,
     7             // DisposableBean interface, custom destroy method.
     8             registerDisposableBean(beanName,
     9                     new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
    10         }
    11         else {
    12             // A bean with a custom scope...
    13             Scope scope = this.scopes.get(mbd.getScope());
    14             if (scope == null) {
    15                 throw new IllegalStateException("No Scope registered for scope '" + mbd.getScope() + "'");
    16             }
    17             scope.registerDestructionCallback(beanName,
    18                     new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
    19         }
    20     }
    21 }

    其中第3行第一个判断为必须不是prototype(原型)的,第二个判断requiresDestruction方法的实现为:

    1 protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
    2     return (bean != null &&
    3             (bean instanceof DisposableBean || mbd.getDestroyMethodName() != null ||
    4                     hasDestructionAwareBeanPostProcessors()));
    5 }

    要注册销毁方法,Bean需要至少满足以下三个条件之一:

    (1)Bean是DisposableBean的实现类,此时执行DisposableBean的接口方法destroy()

    (2)Bean标签中有配置destroy-method属性,此时执行destroy-method配置指定的方法

    (3)当前Bean对应的BeanFactory中持有DestructionAwareBeanPostProcessor接口的实现类,此时执行DestructionAwareBeanPostProcessor的接口方法postProcessBeforeDestruction

    在满足上面三个条件之一的情况下,容器便会注册销毁该Bean,注册Bean的方法很简单,见registerDisposableBean方法实现:

    1 public void registerDisposableBean(String beanName, DisposableBean bean) {
    2     synchronized (this.disposableBeans) {
    3         this.disposableBeans.put(beanName, bean);
    4     }
    5 }

    容器销毁的时候,会遍历disposableBeans,逐一执行销毁方法。

    流程总结

    本文和上篇文章分析了Spring Bean初始化的步骤,最后用一幅图总结一下Spring Bean初始化的流程:

    图只是起梳理流程作用,抛砖引玉,具体代码实现还需要网友朋友们照着代码自己去一步一步分析。

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  • 原文地址:https://www.cnblogs.com/xrq730/p/6363055.html
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