7.Spring源码之路-DefaulListableBeanFactory - FactoryBeanRegistrySupport

总结

1. FactoryBeanRegistrySupport 是抽象类继承了DefaultSingletonBeanRegistry那就拥有了单例Bean注册的所有功能，此外又扩展了FactoryBean的Bean的支持。
2. FactoryBean也是一个Bean，主要作用就是通过工厂方法获取Bean的一种方式，可以让用户通过实现FactoryBean接口，来进行创建Bean.
3. 这里有一个方法protected Object postProcessObjectFromFactoryBean(Object object, String beanName)是当调用FactoryBean的getObject()方法以后允许对Bean进行一些后置处理。属于扩展方法。
4. 这个类中的成员变量private final Map factoryBeanObjectCache = new ConcurrentHashMap<>(16);主要是缓存通过FactoryBean的getObject()方法构造出来的单例Bean。这里发现缓存通过FactoryBean的getObject()方法构造出来的单例Bean的Map和正常的单例Bean实例存放的map不是同一个。DefaultSingletonBeanRegistry的singletonObjects中存放FactoryBean的单例实例，而factoryBeanObjectCache中存放的是由FactoryBean的getObject()方法所产生的实例，所以并不冲突

源码注释的大概翻译

/**
 * 支持需要处理
 * {@link org.springframework.beans.factory.FactoryBean}实例的单例注册表的基类，并与
 * {@link DefaultSingletonBeanRegistry}的单例管理集成在一起。 
 *
 * 用作{@link AbstractBeanFactory}的基类。 
 * @author Juergen Hoeller
 * @since 2.5.1
 */
public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

	/** 由FactoryBeans创建的单例对象的缓存：对象的FactoryBean名称。 */
	private final Map factoryBeanObjectCache = new ConcurrentHashMap<>(16);


	/**
	 * 确定给定FactoryBean的类型。 
	 * @param factoryBean 要检查的FactoryBean实例
	 * @return  返回FactoryBean的对象类型，或者如果尚未确定类型，则返回{@code null} 
	 * or {@code null} if the type cannot be determined yet
	 */
	@Nullable
	protected Class getTypeForFactoryBean(final FactoryBean factoryBean) {
		try {
			if (System.getSecurityManager() != null) {
				return AccessController.doPrivileged((PrivilegedAction>)
						factoryBean::getObjectType, getAccessControlContext());
			}
			else {
				return factoryBean.getObjectType();
			}
		}
		catch (Throwable ex) {
			// Thrown from the FactoryBean's getObjectType implementation.
			logger.info("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;
		}
	}

	/**
	 * 以缓存形式从给定的FactoryBean获取要公开的对象
	 * 快速检查最小同步。 
	 * @param beanName bean的名称
	 * @return 返回从FactoryBean获得的对象，如果不可用返回 {@code null}
	 */
	@Nullable
	protected Object getCachedObjectForFactoryBean(String beanName) {
		return this.factoryBeanObjectCache.get(beanName);
	}

	/**
	 * 获取要从给定FactoryBean中公开的对象
	 * @param factory factoryFactory实例的工厂
	 * @param beanName Bean的名称
	 * @param shouldPostProcess Bean是否要进行后处理
	 * @return 返回从FactoryBean获得的对象
	 * @throws BeanCreationException 如果FactoryBean对象创建失败
	 * @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;
		}
	}

	/**
	 * 获取要从给定FactoryBean中公开的对象。
	 * @param factory FactoryBean实例
	 * @param beanName Bean的名称
	 * @return 返回从FactoryBean获得的对象
	 * @throws BeanCreationException 如果FactoryBean对象创建失败
	 * @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