监听器综合案例

本案例实现一个登录功能，管理员登录时，可以踢用户下线。

案例的bug及解决方案：

附上代码：

MyServletContextListener.java

package com.listener;import java.util.HashMap;import java.util.Map;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.http.HttpSession;import com.bean.User;public class MyServletContextListener implements ServletContextListener {@Overridepublic void contextDestroyed(ServletContextEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void contextInitialized(ServletContextEvent arg0) {ServletContext context=arg0.getServletContext();Map<User,HttpSession>map=new HashMap<User,HttpSession>();context.setAttribute("map",map);}}

MySessionListener.java

package com.listener;import java.util.Map;import javax.servlet.ServletContext;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;import com.bean.User;public class MySessionListener implements HttpSessionAttributeListener,HttpSessionListener {@Overridepublic void attributeAdded(HttpSessionBindingEvent arg0) {HttpSession session=arg0.getSession();ServletContext context=session.getServletContext();Map<User,HttpSession>map=(Map<User, HttpSession>) context.getAttribute("map");map.put((User) session.getAttribute(arg0.getName()),session);}@Overridepublic void attributeRemoved(HttpSessionBindingEvent arg0) {}@Overridepublic void attributeReplaced(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void sessionCreated(HttpSessionEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void sessionDestroyed(HttpSessionEvent arg0) {HttpSession session=arg0.getSession();User u=(User) session.getAttribute("user");Map<User,HttpSession>map=(Map<User, HttpSession>) session.getServletContext().getAttribute("map");map.remove(u);}}

CheckUserExist.java

package com.servlet;import java.util.ArrayList;import java.util.List;import com.bean.User;public class CheckUserExist {private static List<User>users=null;public static void init(){users=new ArrayList<User>();User u=new User();u.setId(1);u.setUsername("zhangsan");u.setPassword("123");users.add(u);User u1=new User();u1.setId(2);u1.setUsername("lisi");u1.setPassword("123");users.add(u1);User u2=new User();u2.setId(3);u2.setUsername("wangwu");u2.setPassword("123");users.add(u2);User u3=new User();u3.setId(4);u3.setUsername("admin");u3.setPassword("123");users.add(u3);}public static User findUser(String username,String password){if(users==null){init();}for(int i=0;i<users.size();++i){if(users.get(i).getUsername().equals(username)&&users.get(i).getPassword().equals(password)){return users.get(i);}}return null;}}

DaoLogin.java

package com.servlet;import java.io.IOException;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 com.bean.User;public class DaoLogin extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username=request.getParameter("username");String password=request.getParameter("password");User user=CheckUserExist.findUser(username, password);if(user!=null){request.getSession().invalidate();//若是用户在同一个浏览器登录，则应把过去的登录状态移除掉，即把Session销毁Map<User,HttpSession>map=(Map<User, HttpSession>) getServletContext().getAttribute("map");for(User u:map.keySet()){if(u.getUsername().equals(username)){map.get(u).invalidate();//若是用户已经登录，则把过去登录的用户移除，确保一个帐号同一时间最多一个人登录break;}} request.getSession().setAttribute("user", user);response.sendRedirect("/ListenerProject/list.jsp");return ;}else{request.setAttribute("msg", "用户名或密码错误");   request.getRequestDispatcher("/login.jsp").forward(request, response);  return ;}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}


KickServlet.java
package com.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.Map;import java.util.Map.Entry;import javax.servlet.ServletContext;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 com.bean.User;public class KickServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String id=request.getParameter("id");Map<User,HttpSession>map=(Map<User, HttpSession>) request.getSession().getServletContext().getAttribute("map");for(Entry e:map.entrySet()){User u=(User)e.getKey();if(u.getId()==Integer.parseInt(id)){map.get(u).invalidate();break;}}response.sendRedirect("/ListenerProject/list.jsp");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}}
login.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <body>  <div style="color:red;">${msg}</div>    <form action="/ListenerProject/servlet/DaoLogin" method="post">    用户名：<input type="text" name="username">  <br/>    密码：<input type="password" name="password"> <br/>     <input type="submit" name="登录">    </form>  </body></html>

list.jsp
<%@ page language="java" import="java.util.*,com.bean.*" pageEncoding="UTF-8"%><%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">        <title>My JSP 'list.jsp' starting page</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><h1> 当前用户  ${user.username}<br/></h1>在线用户:<br/>  <c:forEach items="${applicationScope.map}" var="entry"> ${entry.key.username}      <c:if test="${'admin' != entry.key.username  && user.username == 'admin'}">  <a href="/ListenerProject/servlet/KickServlet?id=${entry.key.id}">踢下去</a>  </c:if>  <br/> </c:forEach>   </body></html>
























                                             
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