spring boot實戰(第二篇)事件監聽

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

前言

spring boot在啟動過程中增加事件監聽機制，為用戶功能拓展提供極大的便利。

支持的事件類型四種

ApplicationStartedEvent

ApplicationEnvironmentPreparedEvent

ApplicationPreparedEvent

ApplicationFailedEvent

實現監聽步驟：

1.監聽類實現ApplicationListener接口 
2.將監聽類添加到SpringApplication實例

ApplicationStartedEvent

ApplicationStartedEvent：spring boot啟動開始時執行的事件

創建對應的監聽類 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 啟動監聽類 * * @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); @Override public void onApplicationEvent(ApplicationStartedEvent event) { SpringApplication app = event.getSpringApplication(); app.setShowBanner(false);// 不顯示banner信息 logger.info("==MyApplicationStartedEventListener=="); } }

在該事件中可以獲取到SpringApplication對象，可做一些執行前的設置.

Application.java類

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 對應Enviroment已經准備完畢，但此時上下文context還沒有創建。

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 配置環境事件監聽 * @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<ApplicationEnvironmentPreparedEvent> { 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<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()); } } } } 

 

在該監聽中獲取到ConfigurableEnvironment后可以對配置信息做操作，例如：修改默認的配置信息，增加額外的配置信息等等~~~

ApplicationPreparedEvent

ApplicationPreparedEvent:spring boot上下文context創建完成，但此時spring中的bean是沒有完全加載完成的。

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; /** * 上下文創建完成后執行的事件監聽器 * * @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); @Override public void onApplicationEvent(ApplicationPreparedEvent event) { ConfigurableApplicationContext cac = event.getApplicationContext(); passContextInfo(cac); } /** * 傳遞上下文 * @param cac */ private void passContextInfo(ApplicationContext cac) { //dosomething() } }

 

在獲取完上下文后，可以將上下文傳遞出去做一些額外的操作。

在該監聽器中是無法獲取自定義bean並進行操作的。

ApplicationFailedEvent

ApplicationFailedEvent:spring boot啟動異常時執行事件 
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> { @Override public void onApplicationEvent(ApplicationFailedEvent event) { Throwable throwable = event.getException(); handleThrowable(throwable); } /*處理異常*/ private void handleThrowable(Throwable throwable) { } }

 

在異常發生時，最好是添加虛擬機對應的鈎子進行資源的回收與釋放，能友善的處理異常信息。

在spring boot中已經為大家考慮了這一點，默認情況開啟了對應的功能：

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()方法中進行資源的回收與釋放。

結束語

spring boot提供的四種監聽事件到這里就結束了，針對實際業務可添加自定義的監聽器，下一節當中將會對spring boot中的監聽源碼進行分析，理解為什么是這樣的。