Servlet监听器

来源：互联网发布：数据库入门书籍编辑：程序博客网时间：2024/04/28 08:47

使用Servlet监听器可以统计在线用户的一个例子，具体实现方法如下：
1.通过ServletContext监听初始化一个application对象，保存在线用户列表；
2.通过Session监听当用户登录成功设置Session属性时将用户名保存在列表中；
3.通过Session监听当用户注销登录时将用户名从列表中删除。

OnlineListener.java(监听器角色):

package com.hmk.listener;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletContext;import javax.servlet.ServletContextAttributeEvent;import javax.servlet.ServletContextAttributeListener;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class OnlineListener implements ServletContextListener,ServletContextAttributeListener, HttpSessionListener,HttpSessionAttributeListener {private ServletContext application = null ; private HttpSession session = null ;@Overridepublic void contextDestroyed(ServletContextEvent sce) {// TODO Auto-generated method stub}@Overridepublic void contextInitialized(ServletContextEvent sce) {//初始化一个application对象 this.application=sce.getServletContext() ; //设置一个列表属性，用于保存在线用户名 this.application.setAttribute("online", new ArrayList()) ;}@Overridepublic void attributeAdded(ServletContextAttributeEvent scab) {// TODO Auto-generated method stub}@Overridepublic void attributeRemoved(ServletContextAttributeEvent scab) {// TODO Auto-generated method stub}@Overridepublic void attributeReplaced(ServletContextAttributeEvent scab) {// TODO Auto-generated method stub}@Overridepublic void sessionCreated(HttpSessionEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void sessionDestroyed(HttpSessionEvent se) {//取得用户名列表 List online=(List)this.application.getAttribute("online") ; //取得当前用户名 String username=(String)se.getSession().getAttribute("username") ; //将此用户名从列表中删除 System.out.println("--删除：--"+username);online.remove(username) ; //将删除后的列表重新设置到application属性中 this.application.setAttribute("online", online) ; }@Overridepublic void attributeAdded(HttpSessionBindingEvent se) {//取得用户名列表 List online=(List)this.application.getAttribute("online") ; //将当前用户名添加到列表中 online.add(se.getValue()) ; //将添加后的列表重新设置到application属性中 this.application.setAttribute("online", online) ;}@Overridepublic void attributeRemoved(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void attributeReplaced(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stub}}

web.xml配置文件

<listener>
<listener-class>com.hmk.listener.OnlineListener</listener-class>
</listener>

jsp页面（onlinelistener.jsp）：

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><%@ page import="java.util.*"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body><form action="onlinelistener.jsp" method="post">用户名：<input type="text" name="username" /><input type="submit" value="登录" /><a href="logout.jsp" mce_href="logout.jsp">注销</a></form><%String username = request.getParameter("username");if (username != null) {session.setAttribute("username", username);}%><p><h3>在线用户：</h3><hr><%List online = (List) getServletContext().getAttribute("online");Iterator iter = online.iterator();while (iter.hasNext()) {%><li><%=iter.next()%></li><%}%></body></html>

jsp页面（logout.jsp）：

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>注销</title></head><body><%session.invalidate();response.setHeader("refresh", "3;URL=onlinelistener.jsp");%><h3>注销成功！</h3>3秒后自动返回登录页面<br>如果没有跳转，请点<a href="onlinelistener.jsp" mce_href="onlinelistener.jsp">这里</a></body></html>