第三章 spring-bean之FactoryBeanRegistrySupport（4）

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前言

从FactoryBeanRegistrySupport类的名字可以看出FactoryBeanRegistrySupport负责FactoryBean的注册与支持。如果想知道FactoryBean相关的资料，请阅读spring-bean中关于FactoryBean的解读。

源码解读

public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

	//  缓存singleton性质的FactoryBean从getObject得到的对象
	private final Map factoryBeanObjectCache = new ConcurrentHashMap(16);

	// 从factoryBean.getObjectType()中得到obejctTpye。
	protected Class getTypeForFactoryBean(final FactoryBean factoryBean) {
		try {
			if (System.getSecurityManager() != null) {
				return AccessController.doPrivileged(new PrivilegedAction>() {
					@Override
					public Class run() {
						return factoryBean.getObjectType();
					}
				}, getAccessControlContext());
			}
			else {
				return factoryBean.getObjectType();
			}
		}
		catch (Throwable ex) {
			// Thrown from the FactoryBean's getObjectType implementation.
			logger.warn("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;
		}
	}

// 通过beanName从缓存中得到对象
	protected Object getCachedObjectForFactoryBean(String beanName) {
		Object object = this.factoryBeanObjectCache.get(beanName);
		return (object != NULL_OBJECT ? object : null);
	}

	//  调用getCachedObjectForFactoryBean之后，识别结果为空，才会调用getObjectFromFactoryBean方法
	//
	protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
		if (factory.isSingleton() && containsSingleton(beanName)) {
			synchronized (getSingletonMutex()) {// 获得DefaultSingletonBeanRegistry中的锁
				Object object = this.factoryBeanObjectCache.get(beanName);// 在并发时候，线程A,B注入A(FactoryBean)，A线程注册时，没有,
				if (object == null) {// A线程注册时，没有, 就从FactoryBean 得到 object
					object = doGetObjectFromFactoryBean(factory, beanName);// 从FactoryBean 得到 object
					// 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);// 为什么在次操作，上面英语给出了答案
					if (alreadyThere != null) {
						object = alreadyThere;
					}
					else {
						if (object != null && shouldPostProcess) {
							try {
								object = postProcessObjectFromFactoryBean(object, beanName);// 处理从FactoryBean得到的对象
							}
							catch (Throwable ex) {
								throw new BeanCreationException(beanName,
										"Post-processing of FactoryBean's singleton object failed", ex);
							}
						}
						this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));//保存在缓存中
					}
				}
				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;
		}
	}

	// 执行调用FactoryBean.getObject()方法而已
	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