Spring bean加载2--FactoryBean情况处理

在Spring bean加载过程中,每次bean实例在返回前都会调用getObjectForBeanInstance来处理FactoryBean的情况.
这边的FactoryBean,Spring设计用于新建复杂bean的,联想下GOF设计模式的创建型,一样的为了解决复杂的bean实例化过程.
其实这边的FactoryBean就是一个factory method[gof定义的意图:定义一个用于创建对象的接口,让子类决定实例化哪个类.Factory Method使一个类的实例化延迟到其子类].这边的处理主要涉及3个方法,我们来看看3个方法各自的职责:

getObjectForBeanInstance: 参数校验之类的准备工作
getObjectFromFactoryBean: 单例时,确保实例是全局唯一的
doGetObjectFromFactoryBean: 实实在在的实例化

参数校验之类的准备工作

AbstractBeanFactory的getObjectForBeanInstance处理.

如果name制定要获取FactoryBean本身实例,而beanInstance却又不是FactoryBean,直接抛异常
如果不需要调用getObject实例化,直接返回实例
尝试从缓存中获取实例[FactoryBeanRegistrySupport负责]
准备beanDefinition,委托getObjectFromFactoryBean处理

单例时保障实例全局唯一

FactoryBeanRegistrySupport的getObjectFromFactoryBean处理
FactoryBeanRegistrySupport负责FactoryBean相关的操作,并缓存FactoryBean的getObject实例化的bean.

判断factory是单例,同时已经new好了（后面需要调用getObject获取目标对象,这边需要factory已经实例化）
单例时,先尝试去缓存找;如果找不到或者不是单例,委托doGetObjectFromFactoryBean实例化一个
由于这样新建就没有机会调用BeanPostProcessor了,所以这边直接调用其postProcessAfterInitialization[职责职责职责,AbstractAutowireCapableBeanFactory干的]
缓冲得到的实例

实例化,干活的

FactoryBeanRegistrySupport的doGetObjectFromFactoryBean处理
这边做的事很少,就是调用factoryBean的getObject,然后如果实例化得到的对象为空抛异常.

源码摘要

AbstractBeanFactory

/** * Get the object for the given bean instance, either the bean * instance itself or its created object in case of a FactoryBean. * 返回bean 实例的对象,可能是实例本身,也可能是FactoryBean新建的对象 * @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） {// 如果想要获取FactoryBean本身,那么beanInstance必须是FactoryBean的实例// 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（））;}// 如果instance不是FactoryBean实例,或者想要获取的就是FactoryBean实例,那么直接返回就好// 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） {// 获取缓存的实例object = getCachedObjectForFactoryBean（beanName）;}if （object == null） {// 缓存中没有对象,那么从头准备bean defition实例化一个// 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;}

FactoryBeanRegistrySupport

/** * Obtain an object to expose from the given FactoryBean, if available * in cached form. Quick check for minimal synchronization. * 获取缓存的,通过FactoryBean暴露出来的对象 * @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）;// 类似<重构>中Introduce NUll Object,只是这边的NULL_OBJECT是Object类型的,没有解决Martin说的"不需要询问对象类型,就可以直接调用行为的方法"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） {// factory是单例的同时,还得已经被实例化（感觉这个检验怪怪的,没想明白）if （factory.isSingleton（） && containsSingleton（beanName）） {synchronized （getSingletonMutex（）） {Object object = this.factoryBeanObjectCache.get（beanName）;if （object == null） {// 缓存中找不到,就自己干吧,实例化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 {// 外面BeanPostProcessor作用在factory上,没有作用在实际想要的实例上,这边补一个// 也就是说,BeanPostProcessor的postProcessBeforeInitialization不会作用在FactoryBean上object = postProcessObjectFromFactoryBean（object, beanName）;}catch （Throwable ex） {throw new BeanCreationException（beanName,"Post-processing of FactoryBean"s singleton object failed", ex）;}}// 缓存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>（） {@Overridepublic 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;}

AbstractAutowireCapableBeanFactory

/** * 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 */@Overrideprotected Object postProcessObjectFromFactoryBean（Object object, String beanName） {return applyBeanPostProcessorsAfterInitialization（object, beanName）;}@Overridepublic 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;}

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