本文为大家分享了servlet监听器的具体学习内容,供大家参考,具体内容如下
1.什么是servlet监听器?
servlet监听器也叫web监听器。是servlet中一种特殊类。能够帮助开发者监听web应用中的特定事件。比如ServletContext,ServletSession,ServletRequest的创建和销毁,变量的创建和销毁等。
2 监听器常用的用途
通常使用Web监听器做以下的内容:
统计在线人数,利用HttpSessionLisener
加载初始化信息:利用ServletContextListener
统计网站访问量
实现访问监控
3.监听器的分类
根据servlet对象可以将监听器划分为三种:ServletContext,ServletSession,ServletRequest。
4监听器的应用
4.1 ServletContex :对应监控application内置对象的创建和销毁。
当web容器开启时,执行contextInitialized方法;当容器关闭或重启时,执行contextDestroyed方法。
实现方式:直接实现ServletContextListener接口
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package com.learn; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import java.io.*; /** * Created by Administrator on 2017/09/23. */ public class MyServletContextListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) { System.out.println( "Webapp initital......." ); ServletContext servletContext = sce.getServletContext(); InputStreamReader inputStreamReader = new InputStreamReader(servletContext.getResourceAsStream( "/count/count.txt" )); BufferedReader bufferedReader = new BufferedReader(inputStreamReader); try { int icount = Integer.parseInt(bufferedReader.readLine()); icount++; servletContext.setAttribute( "count" ,icount); System.out.println( "Webapp initital success" ); } catch (IOException e) { e.printStackTrace(); } } @Override public void contextDestroyed(ServletContextEvent sce) { System.out.println( "webApp destroyed ........" ); ServletContext servletContext = sce.getServletContext(); Integer count = (Integer) servletContext.getAttribute( "count" ); if (count != null ){ count ++; String filePath = servletContext.getRealPath( "/count" ); filePath = filePath+ "/count.txt" ; try { PrintWriter printWriter = new PrintWriter(filePath); printWriter.write(count); printWriter.close(); System.out.println( "webApp desdroyed success " ); } catch (FileNotFoundException e) { e.printStackTrace(); } } } } |
4.2HttpSession监控:对应监控session内置对象的创建和销毁。
当打开一个新的页面时,开启一个session会话,执行sessionCreated方法;当页面关闭session过期时,或者容器关闭销毁时,执行sessionDestroyed方法。
实现方式:直接实现HttpSessionListener接口:
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package com.learn; import javax.servlet.http.HttpSession; import javax.servlet.http.HttpSessionEvent; import javax.servlet.http.HttpSessionListener; /** * Created by Administrator on 2017/09/23. */ public class MySessionListener implements HttpSessionListener{ @Override public void sessionCreated(HttpSessionEvent se) { HttpSession session = se.getSession(); System.out.println( "新建session,sessionId:" +session.getId()); } @Override public void sessionDestroyed(HttpSessionEvent se) { HttpSession session = se.getSession(); System.out.println( "销毁session,sessionId:" +session.getId()); } } |
4.3ServletRequest监控:对应监控request内置对象的创建和销毁。
当访问某个页面时,出发一个request请求,执行requestInitialized方法;当页面关闭时,执行requestDestroyed方法。
实现方式,直接实现ServletRequestListener接口:
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package com.learn; import javax.servlet.ServletRequestEvent; import javax.servlet.ServletRequestListener; import javax.servlet.http.HttpServletRequest; /** * Created by Administrator on 2017/09/23. */ public class MyRequestListener implements ServletRequestListener { @Override public void requestDestroyed(ServletRequestEvent sre) { HttpServletRequest request = (HttpServletRequest) sre.getServletRequest(); Long date = System.currentTimeMillis()-(Long) (request.getAttribute( "dateCreated" )); System.out.println( "消耗时间:" +date); } @Override public void requestInitialized(ServletRequestEvent sre) { HttpServletRequest request = (HttpServletRequest) sre.getServletRequest(); String uri = request.getRequestURI(); uri = request.getQueryString() == null ? uri : (uri + "?" + request.getQueryString()); request.setAttribute( "dateCreated" , System.currentTimeMillis()); System.out.println( "IP:" +request.getRemoteAddr()+ "URI:" +uri); } } |
5监听器web.xml的配置
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< listener > < listener-class >com.learn.MyServletContextListener</ listener-class > </ listener > < listener > < listener-class >com.learn.MySessionListener</ listener-class > </ listener > < listener > < listener-class >com.learn.MyRequestListener</ listener-class > </ listener > |
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。
原文链接:http://www.cnblogs.com/wwyx-xi/p/7582515.html