Spring 源码阅读 16：初始化事件广播器 & 注册事件监听器

// Initialize event multicaster for this context.initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.onRefresh();
// Check for listener beans and register them.registerListeners();

protectedvoidinitApplicationEventMulticaster() {
ConfigurableListableBeanFactorybeanFactory=getBeanFactory();
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicationEventMulticaster=beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isTraceEnabled()) {
logger.trace("Using ApplicationEventMulticaster ["+this.applicationEventMulticaster+"]");
      }
   }
else {
this.applicationEventMulticaster=newSimpleApplicationEventMulticaster(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() +"]");
      }
   }
}

/*** Template method which can be overridden to add context-specific refresh work.* Called on initialization of special beans, before instantiation of singletons.* <p>This implementation is empty.* @throws BeansException in case of errors* @see #refresh()*/protectedvoidonRefresh() throwsBeansException {
// For subclasses: do nothing by default.}

@FunctionalInterfacepublicinterfaceApplicationListener<EextendsApplicationEvent>extendsEventListener {
/*** Handle an application event.* @param event the event to respond to*/voidonApplicationEvent(Eevent);
}

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

privatefinalListenerRetrieverdefaultRetriever=newListenerRetriever(false);

publicfinalSet<ApplicationListener<?>>applicationListeners=newLinkedHashSet<>();
publicfinalSet<String>applicationListenerBeans=newLinkedHashSet<>();

@OverridepublicvoidmulticastEvent(ApplicationEventevent) {
multicastEvent(event, resolveDefaultEventType(event));
}
@OverridepublicvoidmulticastEvent(finalApplicationEventevent, @NullableResolvableTypeeventType) {
ResolvableTypetype= (eventType!=null?eventType : resolveDefaultEventType(event));
Executorexecutor=getTaskExecutor();
for (ApplicationListener<?>listener : getApplicationListeners(event, type)) {
if (executor!=null) {
executor.execute(() ->invokeListener(listener, event));
      }
else {
invokeListener(listener, event);
      }
   }
}

protectedvoidinvokeListener(ApplicationListener<?>listener, ApplicationEventevent) {
ErrorHandlererrorHandler=getErrorHandler();
if (errorHandler!=null) {
try {
doInvokeListener(listener, event);
      } catch (Throwableerr) {
errorHandler.handleError(err);
      }
   } else {
doInvokeListener(listener, event);
   }
}
@SuppressWarnings({"rawtypes", "unchecked"})
privatevoiddoInvokeListener(ApplicationListenerlistener, ApplicationEventevent) {
try {
listener.onApplicationEvent(event);
   } catch (ClassCastExceptionex) {
/* 省略异常处理的逻辑 */   }
}