ApplicationListener与ApplicationEvent 使用及源码解析（下）

通过上篇文章ApplicationListener与ApplicationEvent 使用及源码解析（上）可知，监听器列表是从defaultRetriever中的applicationListeners中获取的，那么applicationListeners是什么时候被添加进来的呢

本文就回答下该问题：实际就是从创建AnnotationConfigApplicationContext的时候被添加进来的

1.new AnnotationConfigApplicationContext（）相关操作

	public AnnotationConfigApplicationContext(Class... annotatedClasses) {
		this();
		register(annotatedClasses);
		refresh();
	}

2.跟踪到refresh（），具体实现如下：

	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				...

				// 具体实现在这个方法
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			...
		}
	}

3.跟踪registerListeners（）方法，具体如下：

	protected void registerListeners() {
		// Register statically specified listeners first.
		for (ApplicationListener listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}

		// 获取所有ApplicationListener相关的类名称列表
		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
		for (String listenerBeanName : listenerBeanNames) {
            // 添加到defaultRetriever的applicationListenerBeans中
			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
		}

		// Publish early application events now that we finally have a multicaster...
		Set earlyEventsToProcess = this.earlyApplicationEvents;
		this.earlyApplicationEvents = null;
		if (earlyEventsToProcess != null) {
			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
				getApplicationEventMulticaster().multicastEvent(earlyEvent);
			}
		}
	}

4.跟踪getBeanNamesForType（）方法，具体如下：

    实现类为DefaultListableBeanFactory

	@Override
	public String[] getBeanNamesForType(Class type, boolean includeNonSingletons, boolean allowEagerInit) {
		if (!isConfigurationFrozen() || type == null || !allowEagerInit) {
            // 具体获取的方法
			return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);
		}
        ...
		return resolvedBeanNames;
	}

	private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
		List result = new ArrayList();

		// beanDefinitionNames 是所有被注册的bean
		for (String beanName : this.beanDefinitionNames) {
			// Only consider bean as eligible if the bean name
			// is not defined as alias for some other bean.
			if (!isAlias(beanName)) {
				try {
					...
						if (!matchFound && isFactoryBean) {
							// In case of FactoryBean, try to match FactoryBean instance itself next.
							beanName = FACTORY_BEAN_PREFIX + beanName;
                            // 判断类型是否匹配
							matchFound = (includeNonSingletons || mbd.isSingleton()) && isTypeMatch(beanName, type);
						}
                        // 如果匹配，则添加到result中 
						if (matchFound) {
							result.add(beanName);
						}
					}
				}
				...
			}
		}

		// Check manually registered singletons too.
		...

		return StringUtils.toStringArray(result);
	}

通过以上分析可知：在创建AnnotationConfigApplicationContext的时候，就把所有的监听器添加到defaultRetriever中了