Spring 源码之核心加载方法(8-10) 初始化和注册广播器

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8.initApplicationEventMulticaster

定位: org.springframework.context.support.AbstractApplicationContext#initApplicationEventMulticaster

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/**
 * 初始化MessageSource。 如果在此上下文中未定义，则使用SimpleApplicationEventMulticaster。
 */
protected void initApplicationEventMulticaster() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   // 判断beanFactory中是否有名字为applicationEventMulticaster的bean (即使beanFactory的祖先beanFactory包含也获取不到)
   if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
      // 如果有，从beanFactory中获取
      this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
      if (logger.isTraceEnabled()) {
         logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
      }
   }
   else {
      // 如果没有，新建 SimpleApplicationEventMulticaster 类作为 applicationEventMulticaster 的 Bean;
      this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
      beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
      if (logger.isTraceEnabled()) {
         logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
               "[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
      }
   }
}

9.onRefresh

定位: org.springframework.context.support.AbstractApplicationContext#onRefresh

钩子方法, 由子类实现

10.initApplicationEventMulticaster

定位: org.springframework.context.support.AbstractApplicationContext#initApplicationEventMulticaster

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protected void registerListeners() {
   // Register statically specified listeners first.
   // 遍历应用程序中存在的监听器集合，并将对应的监听器添加到监听器的多路广播器中
   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!
   // 从 BeanFactory 中获取所有实现了 ApplicationListener 接口的 beanName，
   // 并且添加到 applicationEventMulticaster 的 listenerBean 中
   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...
   // 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。同时将他们添加到 applicationEventMulticaster的multicastEvent中
   Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
   this.earlyApplicationEvents = null;
   if (earlyEventsToProcess != null) {
      for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
         getApplicationEventMulticaster().multicastEvent(earlyEvent);
      }
   }
}