Java Servlet实现同一账号后登陆挤掉前一个登陆(类似QQ)

实现类似QQ登陆功能，账号已在一处登陆，在另外一处登陆时，将挤掉前一次的登录。

原理简介：

主要是servlet中对用户登录时的处理，servlet中维护了用户和sessionId的关系以及用户和session的关系，保存在两个map中，当用户登录时会向map中新增一条记录，如果

发现map中已经有了该用户，则将该用户对应的记录删掉，注意是将map中的记录删掉而不是将session销毁，然后在该session中放入给用户提示的信息，再将新用户的信息

放入map中。在页面中需要不断的验证session中有没有提示信息，如果有则说明已经被挤掉，有一点要注意的是，jsp中获取到的session中的attribute是不会自动更新的，也

就是说如果不刷新页面，即使servlet已经向该用户的session中放入了提示信息，页面中也不会得到的，所以这里我们需要用Ajax的方式不断的向服务器发送请求以获取

session中用户提示信息的动态，一旦发现session中有提示信息，就给出提示。

项目结构：



web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>LoginPush</display-name>

<listener>
<listener-class>cn.com.hafx.LoginServlet</listener-class>
</listener>

<servlet>
<servlet-name>login</servlet-name>
<servlet-class>cn.com.hafx.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/login.do</url-pattern>
<url-pattern>/reLogin.do</url-pattern>
<url-pattern>/getUserMsg.do</url-pattern>
</servlet-mapping>

<welcome-file-list>
<welcome-file>login.jsp</welcome-file>
</welcome-file-list>

</web-app>

LoginServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
*
* @author lyh
* @version 2013-4-11
* @see LoginServlet
* @since
*/
public class LoginServlet extends HttpServlet implements HttpSessionListener
{
/**
* 序列号
*/
private static final long serialVersionUID = -2080934157550504694L;

/**
* 日志
*/
private static Log log = LogFactory.getLog(LoginServlet.class);

/**
* 用户和Session绑定关系
*/
public static final Map<String, HttpSession> USER_SESSION = new HashMap<String, HttpSession>();

/**
* seeionId和用户的绑定关系
*/
public static final Map<String, String> SESSIONID_USER = new HashMap<String, String>();

/**
* 实现HttpSessionListener接口监听 监听session的创建事件
*/
@Override
public void sessionCreated(HttpSessionEvent se)
{
String sessionId = se.getSession().getId();

log.info("创建session sessionId= " + sessionId);
}

/**
* 实现HttpSessionListener接口监听 监听session的销毁事件
*/
@Override
public void sessionDestroyed(HttpSessionEvent se)
{
String sessionId = se.getSession().getId();

//当前session销毁时删除当前session绑定的用户信息
//同时删除当前session绑定用户的HttpSession
USER_SESSION.remove(SESSIONID_USER.remove(sessionId));

log.info("销毁session sessionId= " + sessionId);
}

/**
* 用户登录
*/
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{

//获取请求命令
request.setCharacterEncoding("utf-8");
String servletPath = request.getServletPath();
String uri = servletPath.substring(1, servletPath.lastIndexOf(".do"));

try
{
//登录
if ("login".equals(uri))
{
HttpSession session = request.getSession();
String userName = request.getParameter("userName");
String password = request.getParameter("password");

if (userName != null && !"".equals(userName.trim()))
{
//登录成功
if (login(userName, password))
{
//处理用户登录(保持同一时间同一账号只能在一处登录)
userLoginHandle(request);

//添加用户与HttpSession的绑定
USER_SESSION.put(userName.trim(), session);

//添加sessionId和用户的绑定
SESSIONID_USER.put(session.getId(), userName);

log.info("用户[" + userName + "] 已上线...");

session.setAttribute("userName", userName);
session.removeAttribute("userMsg");

//重定向到首页
response.sendRedirect("main.jsp");
}
//登录失败
else
{
log.info("用户[" + userName + "] 登录失败...");

request.setAttribute("msg", "登录失败，请重新登录！");

//response.sendRedirect("login.jsp");
request.getRequestDispatcher("login.jsp").forward(request, response);
}
}
else
{
log.info("用户[" + userName + "] 登录失败...");

request.setAttribute("msg", "登录失败，请重新登录！");

//response.sendRedirect("login.jsp");
request.getRequestDispatcher("login.jsp").forward(request, response);
}
}
//重新登陆
else if ("reLogin".equals(uri))
{
HttpSession session = request.getSession();
String userName = (String)session.getAttribute("userName");
if (session != null)
{
//销毁相关session
//USER_SESSION.remove(SESSIONID_USER.remove(session.getId()));
session.invalidate();
}
if (userName != null && !"".equals(userName))
{
log.info("用户[" + userName + "] 已下线...");
}
//重定向到登录页面
response.sendRedirect("login.jsp");
}
//ajax校验
else if ("getUserMsg".equals(uri))
{
HttpSession session = request.getSession();

response.setContentType("text/html");
response.setCharacterEncoding("utf-8");

PrintWriter out = response.getWriter();
out.print(session.getAttribute("userMsg"));
}
}
catch (Exception e)
{
log.error(e.getClass() + e.getMessage());
PrintWriter out = response.getWriter();
out.print("服务器内部错误！");
}
}

/**
*
* Description:用户登录时的处理  <br>
* @param request
* @see
*/
private void userLoginHandle(HttpServletRequest request)
{
//当前登录的用户
String userName = request.getParameter("userName");

//当前sessionId
//String sessionId = request.getSession().getId();

//删除当前sessionId绑定的用户，用户--HttpSession
//USER_SESSION.remove(SESSIONID_USER.remove(sessionId));

//删除当前登录用户已绑定的HttpSession
HttpSession session = USER_SESSION.remove(userName);
if (session != null)
{
//删除已登录的sessionId绑定的用户
SESSIONID_USER.remove(session.getId());

session.removeAttribute("userName");
session.setAttribute("userMsg", "您的账号已经在另一处登录，您被迫下线！");
}
}

/**
*
* Description: 模拟DB登录判断<br>
* @param userName 用户
* @param password 密码
* @return
* @see
*/
private boolean login(String userName, String password)
{
return ("lyh".equals(userName) && "123456".equals(password));
}

}

login.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>登录</title>
<%
String msg = (String)(request.getAttribute("msg")==null?"":request.getAttribute("msg"));
%>
<script type="text/javascript">
function show(){
if('<%=msg%>'!=''){
alert('<%=msg%>');
}
}
</script>
</head>
<body style="text-align: center" onload="show();">
<form action="login.do" method="post">
<table border="1">
<tr>
<td align="center" colspan="2">
<h3>用户登录</h3>
</td>
</tr>
<tr>
<td align="right">
用户名
</td>
<td align="left">
<input type="text" id="userName" name="userName">
</td>
</tr>
<tr>
<td align="right">
密 码
</td>
<td align="left">
<input type="password" id="password" name="password">
</td>
</tr>
<tr>
<td align="center" colspan="2">
<input type="submit" value="登录">

<input type="reset" value="重置">
</td>
</tr>
</table>
</form>
</body>
</html>

main.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>登录成功</title>
<script type="text/javascript" src="js/jquery-1.4.4.min.js"></script>
</head>
<%
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","No-cache");
response.setDateHeader("Expires", -1);
response.setHeader("Cache-Control", "No-store");
String userName = "";
userName = (String)(session.getAttribute("userName")==null?"":session.getAttribute("userName"));
%>
<script type="text/javascript">
var int;
var userMsg = '';
var i =0;
function checkUserOnline(){
$.ajax({
type:"post",
url:"getUserMsg.do",
dataType : "text",
success:function(data){userMsg = data;},
error:function(){
alert("获取用户信息失败！");
clearInterval(int);
reLogin();
}
});
if(userMsg=='null'||userMsg==''){
return;
}
else{
alert(userMsg);
clearInterval(int);
reLogin();
}
}
function reLogin(){
window.location = "reLogin.do";
}

function checkLogin(){
int = setInterval("checkUserOnline()",500);
}
</script>
<body onload="checkLogin()">
<%
if(!"".equals(userName)){
out.print("登陆成功！<br/>用户名：<span id='userName'>"+userName+"</span><br/><input type='button' value='重新登陆' onclick='reLogin();'/>");
}
%>
</body>
</html>