spring boot实战(第二篇)事件监听

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<ApplicationStartedEvent> {private Logger logger = LoggerFactory.getLogger(MyApplicationStartedEventListener.class);@Overridepublic 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 implementsApplicationListener<ApplicationEnvironmentPreparedEvent> {private Logger logger = LoggerFactory.getLogger(MyApplicationEnvironmentPreparedEventListener.class);@Overridepublic void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {ConfigurableEnvironment envi = event.getEnvironment();MutablePropertySources mps = envi.getPropertySources();if (mps != null) {Iterator<PropertySource<?>> 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<ApplicationPreparedEvent> {private Logger logger = LoggerFactory.getLogger(MyApplicationPreparedEventListener.class);@Overridepublic 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<ApplicationFailedEvent> {@Overridepublic 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() {@Overridepublic void run() {doClose();}};Runtime.getRuntime().addShutdownHook(this.shutdownHook);}}

在doClose()方法中进行资源的回收与释放。