spring事件监听机制
事件机制的主要成员:
- 事件
- 事件监听器(监听事件触发,处理一些事情)
- 事件源(发布事件)
javaSE 提供了一系列自定义事件的标准。
EvenObject,为javaSE提供的事件类型基类,任何自定义事件都必须继承它。
EventListener,为javaSE提供的事件监听器基类,任何自定义事件监听器都得实现。
javaSE未提供事件发布者,由各个应用程序自行实现事件发布者这一角色。
spring提供了ApplicationEventPublisher接口作为事件发布者,并且ApplicationContext接口继承了该接口,担当着事件发布者的角色。但ApplicationContext接口的具体实现各有差异。
spring提供了ApplicationEventMulticaster接口,负责管理ApplicationListener和发布ApplicationEvent。ApplicationContext接口会把事件的相关工作委托给ApplicationEventMulticaster的实现类做,
spring事件机制流程:
- ApplicationContext发布事件
//发布事件 context.publishEvent(event);
实际上是由ApplicationContext的实现AbstractApplicationContext执行发布事件的行为
- 找到事件广播器,广播事件
getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
- 执行SimpleApplicationEventMulticaster中的multicastEvent方法,调用事件监听器的onApplicationEvent()方法
@Override public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { invokeListener(listener, event); } } }
protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) { ErrorHandler errorHandler = getErrorHandler(); if (errorHandler != null) { try { doInvokeListener(listener, event); } catch (Throwable err) { errorHandler.handleError(err); } } else { doInvokeListener(listener, event); } } @SuppressWarnings({"unchecked", "rawtypes"}) private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) { try { listener.onApplicationEvent(event); } catch (ClassCastException ex) { String msg = ex.getMessage(); if (msg == null || matchesClassCastMessage(msg, event.getClass().getName())) { // Possibly a lambda-defined listener which we could not resolve the generic event type for // -> let's suppress the exception and just log a debug message. Log logger = LogFactory.getLog(getClass()); if (logger.isDebugEnabled()) { logger.debug("Non-matching event type for listener: " + listener, ex); } } else { throw ex; } } }
自定义事件Demo
- 自定义事件
package com.spring.event.event; import org.springframework.context.ApplicationEvent; import com.spring.event.bean.Notify; /** * 自定义事件 * @author sxq * @time 2018年8月31日 上午10:26:24 * */ public class NotifyEvent extends ApplicationEvent { private int version; private Notify notify; public int getVersion() { return version; } public void setVersion(int version) { this.version = version; } /** * serialVersionUID */ private static final long serialVersionUID = -6198589267233914254L; public NotifyEvent(Object source) { super(source); } public Notify getNotify() { return notify; } public void setNotify(Notify notify) { this.notify = notify; } public NotifyEvent(Object source,Notify notify) { this(source); this.notify = notify; } }
- 自定义监听器
package com.spring.event.listner; import org.springframework.context.ApplicationListener; import org.springframework.stereotype.Component; import com.spring.event.event.NotifyEvent; /** * 自定义监听器 * @author sxq * @time 2018年8月31日 上午10:27:04 * */ @Component public class NotifyListenr implements ApplicationListener<NotifyEvent>{ @Override public void onApplicationEvent(NotifyEvent event) { System.out.println(event.getNotify().toString()); //监听事件后,处理后续事情 } }
- 发布
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); Notify notify = new Notify("李四",21); NotifyEvent event = new NotifyEvent("NotifyEvent",notify); event.setVersion(100); //发布事件 context.publishEvent(event);