现在到了ApplicationContext的refresh()方法中初始化消息源与事件广播器，这两个方法比较像，并且逻辑较少，放在一起看看。

initMessageSource

判断beanFactory中是否有名字为messageSource的bean，如果有，从beanFactory中获取并且判断获取的是不是HierarchicalMessageSource类型的，如果是设置其父级消息源

如果没有，新建DelegatingMessageSource类作为messageSource的Bean。

protected void initMessageSource() {
      //获取BeanFactory
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		
		//判断beanFactory中是否有名字为messageSource的bean
		// MESSAGE_SOURCE_BEAN_NAME = "messageSource";
		// 如果没有，新建DelegatingMessageSource类作为messageSource的Bean。
		// 如果有，从beanFactory中获取
		
		if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
			this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
			// Make MessageSource aware of parent MessageSource.
			if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
				HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
				if (hms.getParentMessageSource() == null) {
					// Only set parent context as parent MessageSource if no parent MessageSource
					// registered already.
					hms.setParentMessageSource(getInternalParentMessageSource());
				}
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Using MessageSource [" + this.messageSource + "]");
			}
		}
		else {
			// Use empty MessageSource to be able to accept getMessage calls.
			DelegatingMessageSource dms = new DelegatingMessageSource();
			dms.setParentMessageSource(getInternalParentMessageSource());
			this.messageSource = dms;
			beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
						"': using default [" + this.messageSource + "]");
			}
		}
	}

initApplicationEventMulticaster

初始化ApplicationEventMulticaster，如果beanFactory中不存在的话使用SimpleApplicationEventMulticaster，如果存在使用从beanFactory中获取的。

protected void initApplicationEventMulticaster() {
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		//APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";
		if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
			this.applicationEventMulticaster =
					beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
			}
		}
		else {
			this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
			beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
						APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
						"': using default [" + this.applicationEventMulticaster + "]");
			}
		}
	}

onRefresh

再多说一个onrefresh方法，这个在Spring框架中是没有实现的，留待我们继承可用来在实例化Singleton之前，实例化一些特殊的bean。

registerListeners

这个方法再refresh中也比较简单，都顺便记录下。

1. 获取ApplicationContext初始化的listeners，然后添加到EventMulticaster，这个刚才初始化的，如果为空为SimpleApplicationEventMulticaster的那个
2. 从BeanFactory中获取ApplicationListener类型的Bean，并且添加为ListenerBeans
3. 有些事件可能要提前发出，将需要提前发出的事件发出并置空。

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

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let post-processors apply to them!
		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
		for (String listenerBeanName : listenerBeanNames) {
			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
		}

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

TODO

• AbstractApplicationEventMulticaster类的详细设计

最后

这几个方法比较简单，一起看看