ApplicationEventPublisher是ApplicationContext的父接口之一。这接口的作用是：Interface that encapsulates event publication functionality.
功能就是发布事件，也就是把某个事件告诉的所有与这个事件相关的监听器。
这个接口只有两个方法（这两个是重载方法）。所以把整个接口的代码都贴上来。
/**
* Interface that encapsulates event publication functionality.
* Serves as super-interface for {@link ApplicationContext}.
*
* @author Juergen Hoeller
* @author Stephane Nicoll
* @since 1.1.1
* @see ApplicationContext
* @see ApplicationEventPublisherAware
* @see org.springframework.context.ApplicationEvent
* @see org.springframework.context.event.EventPublicationInterceptor
*/
public interface ApplicationEventPublisher { /**
* Notify all <strong>matching</strong> listeners registered with this
* application of an application event. Events may be framework events
* (such as RequestHandledEvent) or application-specific events.
* @param event the event to publish
* @see org.springframework.web.context.support.RequestHandledEvent
*/
void publishEvent(ApplicationEvent event); /**
* Notify all <strong>matching</strong> listeners registered with this
* application of an event.
* <p>If the specified {@code event} is not an {@link ApplicationEvent},
* it is wrapped in a {@link PayloadApplicationEvent}.
* @param event the event to publish
* @since 4.2
* @see PayloadApplicationEvent
*/
void publishEvent(Object event); }
这个方法会通知的所有与事件相匹配的监听器。这些监听可能是spring框架的监听器，也有可能是特定的监听器。