/**
* 【事件】
* org.springframework.context.ApplicationEvent
* Class to be extended by all application events. 所有 application events根接口
*
* public abstract class ApplicationEvent extends EventObject {
*
* private final long timestamp; // System time when the event happened.
*
* public ApplicationEvent(Object source) {
* super(source);
* this.timestamp = System.currentTimeMillis();
* }
* }
*
*
* 事件分类：
* 1、直接 继承ApplicationEvent的事件
* public class MySpringEvent extends ApplicationEvent{}
*
* 2、任意Java对象的事件
* public class MyEvent {}
*
* 发布的事件被封装在PayloadApplicationEvent中
*
* org.springframework.context.PayloadApplicationEvent
* An ApplicationEvent that carries an arbitrary payload. 一个 携带任意内容的 ApplicationEvent
*
* public class PayloadApplicationEvent extends ApplicationEvent implements ResolvableTypeProvider {
*
* private final T payload;
*
* public PayloadApplicationEvent(Object source, T payload) {
* super(source);
* Assert.notNull(payload, "Payload must not be null");
* this.payload = payload;
* }
* }
*/
/**
* 【事件发布器】
* org.springframework.context.ApplicationEventPublisher
* Interface that encapsulates event publication functionality. 封装事件发布功能的接口；
*
* public interface ApplicationEventPublisher {
* default void publishEvent(ApplicationEvent event) {
* publishEvent((Object) event);
* }
*
* void publishEvent(Object event);
* }
*/
/**
* 【监听器】
* org.springframework.context.ApplicationListener
*
* public interface ApplicationListener extends EventListener {
* void onApplicationEvent(E event);
* }
*
* 监听器类型：
* 1、直接实现ApplicationListener的监听器
* public class MySpringEventListener implements ApplicationListener{}
*
* 由 ApplicationEventMulticaster 调用 自定义监听器 直接执行监听任务
*
* 2、自定义Java类，方法用@EventListener修饰
* public class MyEventListener{
* @EventListener
* void listen(MyEvent event){...}
* }
*
* 由 ApplicationEventMulticaster 调用 ApplicationListenerMethodAdapter 执行监听任务
*
* org.springframework.context.event.GenericApplicationListener
* public interface GenericApplicationListener extends ApplicationListener, Ordered {}
*
* org.springframework.context.event.ApplicationListenerMethodAdapter
* GenericApplicationListener adapter that delegates the processing of an event to an @EventListener annotated method.
* 一个ApplicationListener 用来处理@EventListener注解的方法
*
* public class ApplicationListenerMethodAdapter implements GenericApplicationListener {
*
* public void onApplicationEvent(ApplicationEvent event) {
* processEvent(event);
* }
* }
*/
/**
* 【事件多播器】
* org.springframework.context.event.ApplicationEventMulticaster
* Interface to be implemented by objects that can manage a number of ApplicationListener objects and publish events to them.
* 管理ApplicationListener 并 向ApplicationListener 发布事件；
*/