• 6.2.3-AbstractBeanFactory


    AbstractBeanFactory体系:

    这个抽象类中很重要的实现了BeanFactory中得一个方法,doGetBean();

        
        
        
        
        @SuppressWarnings("unchecked")
        protected <T> T doGetBean(
                final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
                throws BeansException {
        // 获取原始的bean name,去除&,解决alias问题
            final String beanName = transformedBeanName(name);
            Object bean;
        // 尝试从缓存中获取bean 调用的是接口中得方法,其实就是Map中存在的那个注册时候注册进去bean
            // Eagerly check singleton cache for manually registered singletons.
            Object sharedInstance = getSingleton(beanName);
            if (sharedInstance != null && args == null) {
                if (logger.isDebugEnabled()) {
                    if (isSingletonCurrentlyInCreation(beanName)) {
                        logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                                "' that is not fully initialized yet - a consequence of a circular reference");
                    }
                    else {
                        logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
                    }
                }
                //// 如果从缓存中或得bean,还需要判断是否是FactoryBean,并调用getObejct
                bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
            }
            //缓存中不存在bean
            else {
                // Fail if we're already creating this bean instance:
                // We're assumably within a circular reference.
                //  // 如果是原型scope,这边又是正在创建,说明有循环依赖,而原型的循环依赖Spring是不解决的
                if (isPrototypeCurrentlyInCreation(beanName)) {
                    throw new BeanCurrentlyInCreationException(beanName);
                }
                    //如果当前容器没有配置bean,那么去父容器查找
                // Check if bean definition exists in this factory.
                BeanFactory parentBeanFactory = getParentBeanFactory();
                if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                    // Not found -> check parent.
                    String nameToLookup = originalBeanName(name);
                    if (args != null) {
                        // Delegation to parent with explicit args.
                        return (T) parentBeanFactory.getBean(nameToLookup, args);
                    }
                    else {
                        // No args -> delegate to standard getBean method.
                        return parentBeanFactory.getBean(nameToLookup, requiredType);
                    }
                }
    
                if (!typeCheckOnly) {
                    markBeanAsCreated(beanName);
                }
    
                try {
                    final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                    checkMergedBeanDefinition(mbd, beanName, args);
    
                     // 实例化类之前,先去容器中获取配置的bean信息,这边需要将之前的GenericBeanDefinition转化为RootBeanDefinition
                // 同时如果父bean的话,需要合并到子bean
                    // Guarantee initialization of beans that the current bean depends on.
                    String[] dependsOn = mbd.getDependsOn();
                    if (dependsOn != null) {
                        for (String dependsOnBean : dependsOn) {
                            if (isDependent(beanName, dependsOnBean)) {
                                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                        "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                            }
                            registerDependentBean(dependsOnBean, beanName);
                            getBean(dependsOnBean);
                        }
                    }
                    //创建单例bean
                    // Create bean instance.
                    if (mbd.isSingleton()) {
                             // 单例情况下,为解决循环依赖,在实例化之前,先新建一个ObjectFactory实例
                        sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                            @Override
                            public Object getObject() throws BeansException {
                                try {
                                    //创建Bean
                                    return createBean(beanName, mbd, args);
                                }
                                catch (BeansException ex) {
                                    // Explicitly remove instance from singleton cache: It might have been put there
                                    // eagerly by the creation process, to allow for circular reference resolution.
                                    // Also remove any beans that received a temporary reference to the bean.
                                    //创建异常直接销毁
                                    destroySingleton(beanName);
                                    throw ex;
                                }
                            }
                        });
                        bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                    }
                    //创建多例bean
                    else if (mbd.isPrototype()) {
                        // It's a prototype -> create a new instance.
                        Object prototypeInstance = null;
                        try {
                            //创建线程进行绑定说明这是一个多例bean
                            beforePrototypeCreation(beanName);
                            prototypeInstance = createBean(beanName, mbd, args);
                        }
                        finally {
                            //移除线程上绑定的多例bean信息
                            afterPrototypeCreation(beanName);
                        }
                        bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                    }
    
                    else {
                        String scopeName = mbd.getScope();
                        final Scope scope = this.scopes.get(scopeName);
                        if (scope == null) {
                            throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
                        }
                        try {
                            Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                                @Override
                                public Object getObject() throws BeansException {
                                    beforePrototypeCreation(beanName);
                                    try {
                                        return createBean(beanName, mbd, args);
                                    }
                                    finally {
                                        afterPrototypeCreation(beanName);
                                    }
                                }
                            });
                            bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                        }
                        catch (IllegalStateException ex) {
                            throw new BeanCreationException(beanName,
                                    "Scope '" + scopeName + "' is not active for the current thread; consider " +
                                    "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                                    ex);
                        }
                    }
                }
                catch (BeansException ex) {
                    cleanupAfterBeanCreationFailure(beanName);
                    throw ex;
                }
            }
        //这边需要对实例进行类型校验,如果与requiredType不一致,需要委托TypeConverter尝试类型转换
            // Check if required type matches the type of the actual bean instance.
            if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
                try {
                    return getTypeConverter().convertIfNecessary(bean, requiredType);
                }
                catch (TypeMismatchException ex) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Failed to convert bean '" + name + "' to required type [" +
                                ClassUtils.getQualifiedName(requiredType) + "]", ex);
                    }
                    throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
                }
            }
            return (T) bean;
        }

    其中主要调用这个方法的有:

        //---------------------------------------------------------------------
        // Implementation of BeanFactory interface
        //---------------------------------------------------------------------
    
        @Override
        public Object getBean(String name) throws BeansException {
            return doGetBean(name, null, null, false);
        }
    
        @Override
        public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
            return doGetBean(name, requiredType, null, false);
        }
    
        @Override
        public Object getBean(String name, Object... args) throws BeansException {
            return doGetBean(name, null, args, false);
        }

    则这个是获取bean的几种方式,对应了doGetBean()中的几种判断。

    具体如下

    1. 获取原始bean name
      1. 根据alia获取原始bean name
      2. 去除FactoryBean时的& [如果是需要获取FactoryBean自省,配置时需要在bean name前添加&]
    2. 尝试从缓存中获取实例
      1. 如果获取到实例,还要委托getObjectForBeanInstance解决FactoryBean的场景,就是调用getObject
    3. 判断原型场景的循环依赖问题,如果是原型同时bean又正在创建,说明是循环依赖,那直接抛异常,spring不尝试解决原型的循环依赖
    4. 如果在本容器中没有定义该bean,需要去父容器查找
      • 如果有参数,结合参数初始化
      • 如果没有参数,需要结合类型初始化,这边的调用是这个分支(当然这边一样没有类型)
    5. 如果不是类型检查,这边需要标记bean正在实例化
    6. bean实例化的准备工作
      1. 合并父bean的定义,并转化GenericBeanDefinition为RootBeanDefinition
      2. 校验BeanDefinition,如果是抽象类或者非原型带参数抛异常[这边注释说的是只有原型才可以配置构造方法的参数]
      3. 解决bean的依赖
        • 注册依赖的bean
        • 递归调用getBean实例化依赖bean
    7. 创建单例的实例
      • 为解决循环依赖问题,这边使用ObjectFactory在实例化前先暴露bean
      • 老规矩,需要委托getObejctForBeanInstance解决FactoryBean的问题
    8. 创建原型实例
      • 创建前的准备工作,使用prototypesCurrentlyInCreation标记bean正在实例化
      • 委托createBean实例化bean
      • 创建后的善后工作,从prototypesCurrentlyInCreation中删除标记
      • 老规矩,委托getObjectForBeanInstance解决工厂方法的问题
    9. 创建其他scope的实例,这边的逻辑结合了单例跟原型的处理逻辑,即使用解决循环依赖的ObjectFactory也使用prototypeCreation的标记
      • 获取作用域scope,并校验是否已配置
      • 使用ObjectFactory提早暴露实例
      • 标记bean正在创建并委托createBean实例化
      • 又是委托getObjectForBeanInstance解决工厂方法问题
    10. 最后需要对创建的实例进行类型校验,如果不一致,这边还需要委托TypeConverter进行类型装换

    关于从父类DefaultSingletonBeanRegistry中继承过来的四种缓存的集合,

        /** 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);

    四种集合的关系:

        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);
            }
        }
    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);
                }
            }
        }
    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);
        }

    4个变量的关系如下:

    • singletonObjects与singletonFactories,earlySingletonObjects,是互斥的.就是一个bean如果在其中任意一个变量中就,不会存在在另一变量中.这三个变量用于记录一个bean的不同状态.
    • 如果bean已经添加到singletonObjects中,那么singltonFactories和earlySinletonObjects都不会考虑
    • singltonFactories中的bean 通过 ObjectFactory的getObject实例化后,添加到earlySingletonObjects
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  • 原文地址:https://www.cnblogs.com/java-synchronized/p/6797061.html
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