session绑定的事件监听器的应用(统计在线用户)-优快云博客

本文介绍了一个基于Java的在线用户列表管理系统，通过单例模式维护一个全局用户列表，并使用HttpSessionBindingListener来监听用户登录和登出事件。同时，还提供了一个无刷新更新用户列表的JavaScript实现。

统计在线用户列表：

1，写一个单例类，增加一个类型为ArrayList的属性，用来存储所有在线的用户（也可以用数据库进行操作）

2，利用session绑定的事件监听器对正常退出系统的用户进行监听

3，考虑用户以浏览器的关闭按钮关闭或以Alt+F4进行关闭（这可以用javascript对用户的操作进行捕捉，网上这方面够多）

4，当非正常关闭，如电脑突然断电，用户直接关闭电脑等，这需要等到session失效后，用户列表中的用户才能清除

共用到了7个文件：

UserList.java /** * 用于存储用户列表的容器 * 这是一个单例类 */ package com.session; import java.util.ArrayList; import java.util.List; public class UserList { private List list; private static UserList instance = null; // 以private的方式来声明构造方法,使得其他的类对象无法调用此类的构造函数 private UserList() { list = new ArrayList(); } public static synchronized UserList getInstance() { if (instance == null) { instance = new UserList(); } return instance; } public void addUser(String userName) { if (userName != null) { list.add(userName); } } public void removeUser(String userName) { if (userName != null) list.remove(userName); } public List getList() { return list; } } UserBinding.java/** * 实现了HttpSessionBindingListener接口, * 以对用户监听,我们必须实现valueBound和 * UnvalueBound方法 */ package com.session; import javax.servlet.http.HttpSessionBindingEvent; import javax.servlet.http.HttpSessionBindingListener; public class UserBinding implements HttpSessionBindingListener { private String userName; private UserList userList = UserList.getInstance(); public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public void valueBound(HttpSessionBindingEvent e) { System.out.println(userName); userList.addUser(userName); System.out.println(userList.getList()); } public void valueUnbound(HttpSessionBindingEvent e) { userList.removeUser(userName); } } UserListServlet.java /** * 对登录用户进行逻辑处理的Servlet程序 */ package com.session; import java.io.IOException; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; public class UserListServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session=request.getSession(); System.out.println(session.getId()); UserBinding user=new UserBinding(); String userName=request.getParameter("userName"); if(null==userName||"".equals(userName)) { return; } //用户名不为空 user.setUserName(userName); session.setAttribute("user", user); // UserList userList=UserList.getInstance(); // //System.out.println(userList.getList()); // request.setAttribute("userList",userList); // // RequestDispatcher rd=request.getRequestDispatcher("../userlist.jsp"); // rd.forward(request,response); response.sendRedirect("../userlist.jsp"); } } LogoutServlet.java /** * 用于注销 */ package com.session; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; public class LogoutServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session = request.getSession(); if (session != null) { session.invalidate(); } response.sendRedirect("../userlist.jsp"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

简单的登录界面：
login.jsp<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>用户登录</title><meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

</head>
<body>
<form action="servlet/UserListServlet" method="POST">
<input type="text" name="userName" >
<input type="submit" name="login" value=" 登录 ">
</form>
</body>
</html>
显示用户列表：
userlist.jsp
<%@ page language="java" import="java.util.*"
contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><%@ page import="com.session.UserList"%>
<%@ taglib prefix="c" uri=" http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>用户列表</title><meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

<script type="text/javascript" src="refresh.js">
</script>
</head>
<body>
<h2>在线用户列表</h2>
<div id="userList">
<%
UserList userList=UserList.getInstance();

List<String> list = userList.getList();
for (int i = 0; i < list.size(); i++)
{
out.println(list.get(i) + "<br>");
}

%>

</div>
<form action="servlet/LogoutServlet" method="GET"><input type="submit" name="logout" value=" 注销 "></form>
</body>
</html>
最后是实现页面无刷新的javascript代码
refresh.js

/*
页面无刷新的javascript代码
*/
window.onload=initAll;

var httpReq=false;
var url="userlist.jsp";

function initAll()
{
	makeRequest(url);
}

function makeRequest(url)
{
	if(window.XMLHttpRequest)// Mozilla, Safari,... 
	{
		httpReq=new XMLHttpRequest();
	}
	else
	{
		if(window.ActiveXObject)//IE
		{
			try
			{
				httpReq=new ActiveXObject("Microsoft.XMLHTTP");
			}
			catch(e){}
		}
	}
	
	if(httpReq)
	{
		httpReq.onreadystatechange=tillRefresh;
		httpReq.open("GET",url,true);//异步
		httpReq.send(null);
	}
	else
	{
		alert("不能创建一个XMLHTTPRequest实例");
	}
	
}
function tillRefresh()
{
	var tempDiv=document.createElement("div");
	var userList=document.getElementById("userList");
	
	if(httpReq.readyState==4)
	{
		if(httpReq.status==200)
		{
			tempDiv.innerHTML=httpReq.responseText;
		
			var required=tempDiv.getElementsByTagName("div");
			userList.innerHTML=required[0].innerHTML;
			
			setTimeout("makeRequest(url)",5000);
		}
		else
		{
			alert("对不起,出现了一些问题 :"+httpReq.status);
		}
	}
}

对用户以浏览器的关闭按钮关闭或以Alt+F4进行关闭的情况没有写出，因为对javascript不太懂，COME ON!!!
<meta http-equiv="pragma" content="no-cache">