public interface SmartInitializingSingleton {
    /**
     * Invoked right at the end of the singleton pre-instantiation phase,
     * with a guarantee that all regular singleton beans have been created
     * already. {@link ListableBeanFactory#getBeansOfType} calls within
     * this method won't trigger accidental side effects during bootstrap.
     * <p><b>NOTE:</b> This callback won't be triggered for singleton beans
     * lazily initialized on demand after {@link BeanFactory} bootstrap,
     * and not for any other bean scope either. Carefully use it for beans
     * with the intended bootstrap semantics only.
     */
    void afterSingletonsInstantiated();
 }
复制代码

for (Method method : annotatedMethods.keySet()) {
    for (EventListenerFactory factory : factories) {
       if (factory.supportsMethod(method)) {
          Method methodToUse = AopUtils.selectInvocableMethod(method, context.getType(beanName));
          ApplicationListener<?> applicationListener =
                factory.createApplicationListener(beanName, targetType, methodToUse);
          if (applicationListener instanceof ApplicationListenerMethodAdapter) {
             ((ApplicationListenerMethodAdapter) applicationListener).init(context, this.evaluator);
          }
          context.addApplicationListener(applicationListener);
          break;
       }
    }
 }
复制代码

public void processEvent(ApplicationEvent event) {
    Object[] args = resolveArguments(event);
    if (shouldHandle(event, args)) {
       Object result = doInvoke(args);
       if (result != null) {
          handleResult(result);
       }
       else {
          logger.trace("No result object given - no result to handle");
       }
    }
 }
复制代码

@Override
 public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
    ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
    Executor executor = getTaskExecutor();
    for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
       if (executor != null) {
          executor.execute(() -> invokeListener(listener, event));
       }
       else {
          invokeListener(listener, event);
       }
    }
 }
复制代码

protected void initApplicationEventMulticaster() {
    ConfigurableListableBeanFactory beanFactory = 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 = 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() + "]");
       }
    }
 }
复制代码

@Component("applicationEventMulticaster")
 public class TestEventMulticaster extends SimpleApplicationEventMulticaster {
 }