http://blog.csdn.net/liaokailin/article/details/48186331

前言

spring boot在启动过程中增加事件监听机制，为用户功能拓展提供极大的便利。

支持的事件类型四种

ApplicationStartedEvent

ApplicationEnvironmentPreparedEvent

ApplicationPreparedEvent

ApplicationFailedEvent

实现监听步骤：

1.监听类实现ApplicationListener接口 

2.将监听类添加到SpringApplication实例

ApplicationStartedEvent

ApplicationStartedEvent：spring boot启动开始时执行的事件

创建对应的监听类 MyApplicationStartedEventListener.java

package com.lkl.springboot.listener;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.boot.SpringApplication;import org.springframework.boot.context.event.ApplicationStartedEvent; import org.springframework.context.ApplicationListener; /** * spring boot 启动监听类 * * @author liaokailin * @version $Id: MyApplicationStartedEventListener.java, v 0.1 2015年9月2日 下午11:06:04 liaokailin Exp $ */ public class MyApplicationStartedEventListener implements ApplicationListener
    
      { private Logger logger = LoggerFactory.getLogger(MyApplicationStartedEventListener.class); @Override public void onApplicationEvent(ApplicationStartedEvent event) { SpringApplication app = event.getSpringApplication(); app.setShowBanner(false);// 不显示banner信息 logger.info("==MyApplicationStartedEventListener=="); } }
    

在该事件中可以获取到SpringApplication对象，可做一些执行前的设置.

Application.java类

package com.lkl.springboot;import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import com.lkl.springboot.listener.MyApplicationStartedEventListener; @SpringBootApplication public class Application { public static void main(String[] args) { SpringApplication app = new SpringApplication(Application.class); app.addListeners(new MyApplicationStartedEventListener()); app.run(args); } }

 

ApplicationEnvironmentPreparedEvent

ApplicationEnvironmentPreparedEvent：spring boot 对应Enviroment已经准备完毕，但此时上下文context还没有创建。

MyApplicationEnvironmentPreparedEventListener.java

package com.lkl.springboot.listener; import java.util.Iterator; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent; import org.springframework.context.ApplicationListener; import org.springframework.core.env.ConfigurableEnvironment; import org.springframework.core.env.MutablePropertySources; import org.springframework.core.env.PropertySource; /** * spring boot 配置环境事件监听 * @author liaokailin * @version $Id: MyApplicationEnvironmentPreparedEventListener.java, v 0.1 2015年9月2日 下午11:21:15 liaokailin Exp $ */ public class MyApplicationEnvironmentPreparedEventListener implements ApplicationListener
    
      { private Logger logger = LoggerFactory.getLogger(MyApplicationEnvironmentPreparedEventListener.class); @Override public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) { ConfigurableEnvironment envi = event.getEnvironment(); MutablePropertySources mps = envi.getPropertySources(); if (mps != null) { Iterator
     
      > iter = mps.iterator(); while (iter.hasNext()) { PropertySource
       ps = iter.next(); logger .info("ps.getName:{};ps.getSource:{};ps.getClass:{}", ps.getName(), ps.getSource(), ps.getClass()); } } } }
     
    

 

在该监听中获取到ConfigurableEnvironment后可以对配置信息做操作，例如：修改默认的配置信息，增加额外的配置信息等等~~~

ApplicationPreparedEvent

ApplicationPreparedEvent:spring boot上下文context创建完成，但此时spring中的bean是没有完全加载完成的。

MyApplicationPreparedEventListener.java

package com.lkl.springboot.listener;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.boot.context.event.ApplicationPreparedEvent;import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationListener; import org.springframework.context.ConfigurableApplicationContext; /** * 上下文创建完成后执行的事件监听器 * * @author liaokailin * @version $Id: MyApplicationPreparedEventListener.java, v 0.1 2015年9月2日 下午11:29:38 liaokailin Exp $ */ public class MyApplicationPreparedEventListener implements ApplicationListener
    
      { private Logger logger = LoggerFactory.getLogger(MyApplicationPreparedEventListener.class); @Override public void onApplicationEvent(ApplicationPreparedEvent event) { ConfigurableApplicationContext cac = event.getApplicationContext(); passContextInfo(cac); } /** * 传递上下文 * @param cac */ private void passContextInfo(ApplicationContext cac) { //dosomething() } }
    

 

在获取完上下文后，可以将上下文传递出去做一些额外的操作。

在该监听器中是无法获取自定义bean并进行操作的。

ApplicationFailedEvent

ApplicationFailedEvent:spring boot启动异常时执行事件 

MyApplicationFailedEventListener.java

package com.lkl.springboot.listener;import org.springframework.boot.context.event.ApplicationFailedEvent;import org.springframework.context.ApplicationListener;public class MyApplicationFailedEventListener implements ApplicationListener
    
      { @Override public void onApplicationEvent(ApplicationFailedEvent event) { Throwable throwable = event.getException(); handleThrowable(throwable); } /*处理异常*/ private void handleThrowable(Throwable throwable) { } }
    

 

在异常发生时，最好是添加虚拟机对应的钩子进行资源的回收与释放，能友善的处理异常信息。

在spring boot中已经为大家考虑了这一点，默认情况开启了对应的功能：

public void registerShutdownHook() {        if (this.shutdownHook == null) { // No shutdown hook registered yet. this.shutdownHook = new Thread() { @Override public void run() { doClose(); } }; Runtime.getRuntime().addShutdownHook(this.shutdownHook); } }

 

在doClose()方法中进行资源的回收与释放。

结束语

spring boot提供的四种监听事件到这里就结束了，针对实际业务可添加自定义的监听器，下一节当中将会对spring boot中的监听源码进行分析，理解为什么是这样的。