Spring5源码浅析(八)—FactoryBeanRegistrySupport

        在前两篇《Spring5源码浅析(七)—DefaultSingletonBeanRegistry(上)》和《Spring5源码浅析(七)—DefaultSingletonBeanRegistry(下)》中,我给大家详细分析了DefaultSingletonBeanRegistry这个类,从中我们知道DefaultSingletonBeanRegistry主要侧重于Bean的注册,销毁,以及依赖关系(关联关系)的注册和销毁。本篇呢,我们继续沿着DefaultListableBeanFactory的继承线往下移,所以我们来看一下DefaultSingletonBeanRegistry的子类---FactoryBeanRegistrySupport.

      我们首先来看这个抽象类中,最长的方法getObjectFromFactoryBean,源码如下所示:

/**
	 * 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) {
		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 (shouldPostProcess) {
							if (isSingletonCurrentlyInCreation(beanName)) {
								// Temporarily return non-post-processed object, not storing it yet..
								return object;
							}
							beforeSingletonCreation(beanName);
							try {
								object = postProcessObjectFromFactoryBean(object, beanName);
							}
							catch (Throwable ex) {
								throw new BeanCreationException(beanName,
										"Post-processing of FactoryBean's singleton object failed", ex);
							}
							finally {
								afterSingletonCreation(beanName);
							}
						}
						if (containsSingleton(beanName)) {
							this.factoryBeanObjectCache.put(beanName, object);
						}
					}
				}
				return object;
			}
		}
		else {
			Object object = doGetObjectFromFactoryBean(factory, beanName);
			if (shouldPostProcess) {
				try {
					object = postProcessObjectFromFactoryBean(object, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
				}
			}
			return object;
		}
	}

       在getObjectFromFactoryBean函数中,主要处理两个问题,第一个是工厂是不是单例的,第二个是这个Bean是否需要进一步处理.

         首先,如果传入的工厂是单例的,并且要获取的beanName已经被实例化了,就会使用父类DefaultSingletonBeanRegistry的getSingletonMutex来锁定singletonObjects这个集合(该集合的详细介绍可参考《Spring5源码浅析(七)—DefaultSingletonBeanRegistry(上)》),然后首先从缓存factoryBeanObjectCache中获取bean,如果缓存中已经有了,就直接返回该对象.如果缓存中没有,就调用doGetObjectFromFactoryBean方法来获取object,调用完成之后,因为有可能在调用doGetObjectFromFactoryBean的过程中,该Bean被放到了factoryBeanObjectCache中,所以需要再次校验,如果此时发现缓存中已经有了,那就直接返回就行了,如果此时还没有,我们就会判断一下在父类DefaultSingletonBeanRegistry中的singletonObjects是否已经包含该实例了,如果已经包含了,我们就把这个对象存放到本地缓存(factoryBeanObjectCache)中,在存放缓存之前,会根据shouldPostProcess来决定是否对当前这个对象做进一步的操作,比如为当前这个对象应用beforeSingletonCreation,调用postProcessObjectFromFactoryBean,以及afterSingletonCreation这几个函数.

        其次,如果工厂不是单例的或者要获取的beanName没有被实例化,就会使用doGetObjectFromFactoryBean来获取实例,并根据shouldPostProcess来决定是否为这个对象执行postProcessObjectFromFactoryBean这个函数,最后进行返回.

        现在来看FactoryBeanRegistrySupport中第二长的函数doGetObjectFromFactoryBean,源码如下所示:

    /**
	 * 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((PrivilegedExceptionAction