为servlet项目编写定时任务

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为 java servlet 项目编写servlet包括三个步骤

1、编写web.xml 的 listener 监听器配置，web.xml的侦听器会在web服务器(如tomcat)启动的时候，加载该侦听器 contextInitialized 方法

  <!-- configuration of frame work core listener -->  <listener>    <listener-class>hs.libra.core.task.CTaskListener</listener-class>  </listener>

2、实现侦听器类，注意此类名称和web.xml里的一一对应关系，ServletContextListener.contextInitialized 方法会在侦听器初始化的时候调用。初始化时，创建定期器，由定时器定期执行自动任务。以下程序片段是30分钟自动执行一次。

/**servlet listener of framework core module * if you want to start the listener, you need to configurate it in web.xml of <listener></listener> * by fuzhou huilin corp.ltd @author lms 2016.07.25 */package hs.libra.core.task;import java.util.Date;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;public class CTaskListener implements ServletContextListener {private java.util.Timer timer = null;@Overridepublic void contextInitialized(ServletContextEvent sce) {timer = new java.util.Timer(true);sce.getServletContext().log("initializing system core task...");timer.schedule(new CCoreTask(sce.getServletContext()), new Date(), 30*60*1000);}@Overridepublic void contextDestroyed(ServletContextEvent sce) {sce.getServletContext().log("system core auto task ended.");timer.cancel();}}

3、编写要执行的任务，注意该类是继承了 TimerTask，注意running是static方法，保证单例执行 doTask 任务

/**frame work core work to be executed by CTaskListener * this task realize to GC expiry session object * by fuzhou huilin corp.ltd @author lms 2016.07.25 */package hs.libra.core.task;import hs.libra.core.tool.CSessionUtils;import java.util.TimerTask;import javax.servlet.ServletContext;public class CCoreTask extends TimerTask{private ServletContext sc = null;private static boolean running=false;//constructor method of CCoreTaskpublic CCoreTask(ServletContext sc){this.sc = sc;}@Overridepublic void run() {if (!running){running = true;this.sc.log("start running CCoreTask...");doTask();running = false;this.sc.log("CCoreTask runned.");}}private void doTask(){CSessionUtils.checkExpirySession();}}

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