HttpSessionListener监听器
定义监听器
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package lee; import javax.servlet.*;import javax.servlet.annotation.*;import javax.servlet.http.*;import java.util.*;@WebListenerpublic class OnlineListener implements HttpSessionListener{ // 当用户与服务器之间开始session时触发该方法 public void sessionCreated(HttpSessionEvent se) { HttpSession session = se.getSession(); ServletContext application = session.getServletContext(); // 获取session ID String sessionId = session.getId(); // 如果是一次新的会话 if (session.isNew()) { String user = (String)session.getAttribute("user"); // 未登录用户当游客处理 user = (user == null) ? "游客" : user; Map<String , String> online = (Map<String , String>) application.getAttribute("online"); if (online == null) { online = new Hashtable<String , String>(); } // 将用户在线信息放入Map中 online.put(sessionId , user); application.setAttribute("online" , online); } } // 当用户与服务器之间session断开时触发该方法 public void sessionDestroyed(HttpSessionEvent se) { HttpSession session = se.getSession(); ServletContext application = session.getServletContext(); String sessionId = session.getId(); Map<String , String> online = (Map<String , String>) application.getAttribute("online"); if (online != null) { // 删除该用户的在线信息 online.remove(sessionId); } application.setAttribute("online" , online); }} |
测试JSP
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<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %><%@ page import="java.util.*" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head> <title> 用户在线信息 </title> <meta name="website" content="http://www.crazyit.org" /></head><body>在线用户：<table width="400" border="1"><%Map<String , String> online = (Map<String , String>)application .getAttribute("online");for (String sessionId : online.keySet()){%><tr> <td><%=sessionId%> <td><%=online.get(sessionId)%></tr><%}%></body></html> |
测试结果
HttpSessionListener监听器应用场景
应用场景：用来统计当前在线人数
实现HttpSessionListener
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import javax.servlet.ServletContext;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class MyHttpSessionListener implements HttpSessionListener { @Override public void sessionCreated(HttpSessionEvent httpSessionEvent) { System.out.println("httpsession被创建"); } @Override public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { System.out.println("httpsession被销毁"); } } |
登陆界面去创建HttpSessionListenter
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<%@ page contentType="text/html;charset=UTF-8" language="java" %><html> <head> <title>$Title$</title> </head> <body> <% <%-- 创建HttpSessionListenter--%> request.getSession(); %> </body></html> |
登出销毁HttpSessionListenter
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<%@ page contentType="text/html;charset=UTF-8" language="java" %><html> <head> <title>$Title$</title> </head> <body> <%<%-- 销毁HttpSessionListener--%> request.getSession().invalidate(); %><h1>已退出</h1> </body></html> |
实现统计登陆人数（多线程并发）
web.xml中配置监听
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<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <listener> <listener-class>MyHttpSessionListener</listener-class> </listener> <listener> <listener-class>myServletContextListener</listener-class> </listener></web-app> |
统计人数实在最大ServletContextListener这个域当中
因为HttpSessionListener监听器只在当前会话中有效
（1）创建ServletContextListener监听器并设置初始值为0
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import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;public class myServletContextListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent servletContextEvent) { ServletContext sc = servletContextEvent.getServletContext(); sc.setAttribute("count", 0); } @Override public void contextDestroyed(ServletContextEvent servletContextEvent) { }} |
2）变更在线人数
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import javax.servlet.ServletContext;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class MyHttpSessionListener implements HttpSessionListener { @Override public void sessionCreated(HttpSessionEvent httpSessionEvent) { System.out.println("httpsession被创建"); countPersion( httpSessionEvent.getSession().getServletContext(), true); } @Override public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { System.out.println("httpsession被销毁"); countPersion(httpSessionEvent.getSession().getServletContext(), false); } /* * 变更在线的人数 * */ public void countPersion(ServletContext sc, boolean isAdd) { // 为了防止多线程并发问题加锁 synchronized (sc) { // 获得当前的在线人数 Integer count = (Integer) sc.getAttribute("count"); if(isAdd) { sc.setAttribute("count", ++count); } else { sc.setAttribute("count", --count); } } }} |
（3）前端页面上去获取显示
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<%@ page contentType="text/html;charset=UTF-8" language="java" %><html> <head> <title>$Title$</title> </head> <body> <%<%-- 创建HttpSessionListenter--%> request.getSession(); %> <h1>欢迎登陆</h1> <hr> 当前的在线人数 ${count} <a href="logout.jsp" rel="external nofollow" >退出</a> </body></html> |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/chengqiuming/article/details/100586954
