监听器实栗在线人数统计

实现思路常见的流程是,标准的mvc 即登录表单,用户提交数据到登录检查,若登录检查通过以后,触发session事件,保存进入在线人员列表中,页面跳转到在线用户列表,若用户注销,从在线列表中删除.代码如下使用set集合, 即 set集合去重原因内部存储为map,mqp的键值对为hashcode 由于哈希表的特征即 set可去重项目结构创建迭代器package com.ming.listener;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;import java.util.Set;import java.util.TreeSet;// 对servlet 上下文监听public class OnlineUserList implements HttpSessionAttributeListener, HttpSessionListener, ServletContextListener { private ServletContext servletContext = null; // 增加session属性的时候,触发事件 // session 属性增加 @Override public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) { Set all = (Set)this.servletContext.getAttribute(“online”); all.add(httpSessionBindingEvent.getValue()); this.servletContext.setAttribute(“online”, all); } // 用户注销登录 // session 属性删除 @Override public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) { Set all = (Set)this.servletContext.getAttribute(“online”); all.remove(httpSessionBindingEvent.getValue()); this.servletContext.setAttribute(“online”, all); } @Override public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) { } // 上下文初始化 // 初始化 @Override public void contextInitialized(ServletContextEvent servletContextEvent) { // 获得上下文实栗 this.servletContext = servletContextEvent.getServletContext(); // 设置保存set集合 this.servletContext.setAttribute(“online”, new TreeSet()); } @Override public void contextDestroyed(ServletContextEvent servletContextEvent) { } @Override public void sessionCreated(HttpSessionEvent httpSessionEvent) { } // session 销毁 @Override public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { Set all = (Set)this.servletContext.getAttribute(“online”); all.remove(httpSessionEvent.getSession().getAttribute(“id”)); this.servletContext.setAttribute(“online”, all); }}配置文件<!DOCTYPE web-app PUBLIC “-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN” “http://java.sun.com/dtd/web-app_2_3.dtd" ><web-app> <display-name>Archetype Created Web Application</display-name> <listener> <listener-class>com.ming.listener.OnlineUserList</listener-class> </listener> <filter> <filter-name>LoginFile</filter-name> <filter-class>com.ming.filter.LoginFile</filter-class> </filter> <filter-mapping> <filter-name>LoginFile</filter-name> <url-pattern>/index.jsp</url-pattern> </filter-mapping> <servlet> <servlet-name>login</servlet-name> <servlet-class>com.ming.servlrt.LoginServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>login</servlet-name> <url-pattern>/loginServlet</url-pattern> </servlet-mapping></web-app>在线用户统计<%@ page import=“java.util.Set” %><%@ page import=“java.util.Iterator” %><%@ page import=“javax.swing.text.html.HTMLDocument” %><%– Created by IntelliJ IDEA. User: ming Date: 19-3-17 Time: 上午4:14 To change this template use File | Settings | File Templates.–%><%@ page contentType=“text/html;charset=UTF-8” language=“java” %><html><head> <title>Title</title></head><body>您已经登录显示用户在线<% Set all = (Set)super.getServletContext().getAttribute(“online”); Iterator iterator = all.iterator(); while(iterator.hasNext()){ %> <%=iterator.next()%> <% }%></body></html>运行效果