Spring5源码 - 11 Spring事件监听机制_源码篇

protected void initApplicationEventMulticaster() {
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		//判断IOC容器中包含applicationEventMulticaster 事件多播器的Bean的name
		if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
		    /创建一个applicationEventMulticaster的bean放在IOC 容器中,bean的name 为applicationEventMulticaster
			this.applicationEventMulticaster =beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
			}
		}
		
		else { //容器中不包含一个beanName 为applicationEventMulticaster的多播器组件
		    //创建一个SimpleApplicationEventMulticaster 多播器
			this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
			//注册到容器中
			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 + "]");
			}
		}
	}​

protected void registerListeners() {
		//去容器中把applicationListener 捞取出来注册到多播器上去（系统的）
		for (ApplicationListener<?> listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}

        //开发人员实现了ApplicationListener 的组件
		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
		for (String listenerBeanName : listenerBeanNames) {
			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
		}

	    //在这里之前，我们早期想发布的事件 由于没有多播器没有发布，在这里我们总算有了自己的多播器，可以在这里发布早期堆积的事件了. （早起发布事件，会自动发布，无需调用pubilish）
		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
		this.earlyApplicationEvents = null;
		if (earlyEventsToProcess != null) {
			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
				getApplicationEventMulticaster().multicastEvent(earlyEvent);
			}
		}
	}

org.springframework.context.support.AbstractApplicationContext#publishEvent(java.lang.Object, org.springframework.core.ResolvableType)

public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
		ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
		//获取到所有的监听器
		for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
		    //看spring 容器中是否支持线程池 异步发送事件
			Executor executor = getTaskExecutor();
			if (executor != null) {
				executor.execute(new Runnable() {
					@Override
					public void run() {
					    
						invokeListener(listener, event);
					}
				});
			}
			else {  //同步发送事件
				invokeListener(listener, event);
			}
		}
	}	

private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
		try {
		    //调用对于listener的onApplicationEvent事件
			listener.onApplicationEvent(event);
		}
		catch (ClassCastException ex) {
			String msg = ex.getMessage();
			if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
				// Possibly a lambda-defined listener which we could not resolve the generic event type for
				// -> let's suppress the exception and just log a debug message.
				Log logger = LogFactory.getLog(getClass());
				if (logger.isDebugEnabled()) {
					logger.debug("Non-matching event type for listener: " + listener, ex);
				}
			}
			else {
				throw ex;
			}
		}
	}