本文主要是介绍事件监听之统计登录用户人数（含用户名）案例，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
（一）创建一个User类，用于封装一个用户信息，该类实现了HttpSessionBindingListener接口中的valueBound()方法
和valueUnbound()方法
1 package entity;
2
3 import javax.servlet.annotation.WebListener;
4 import javax.servlet.http.*;
5
6 @WebListener()
7 public class User implements HttpSessionBindingListener {
8
9 private String username;
10 private String password;
11 private String id;
12
13 public String getUsername() {
14 return username;
15 }
16
17 public void setUsername(String username) {
18 this.username = username;
19 }
20
21 public String getPassword() {
22 return password;
23 }
24
25 public void setPassword(String password) {
26 this.password = password;
27 }
28
29 public String getId() {
30 return id;
31 }
32
33 public void setId(String id) {
34 this.id = id;
35 }
36
37 @Override
38 public void valueBound(HttpSessionBindingEvent event) {
39 //将user存入列表
40 OnlineUser.getInstance().addUser(this);
41 }
42
43 @Override
44 public void valueUnbound(HttpSessionBindingEvent event) {
45 OnlineUser.getInstance().removeUser(this);
46 }
47 }（二）创建OnlineUser类，用于存储和获取在用户的列表，而这个列表对于所有的页面来说应该是同一个，故为单例模式。
1 package entity;
2
3 import java.util.HashMap;
4 import java.util.Map;
5
6 public class OnlineUser {
7 private OnlineUser() {}
8 private static OnlineUser instance = new OnlineUser ();
9 public static OnlineUser getInstance() {
10 return instance;
11 }
12 private Map userMap = new HashMap();
13 //将用户添加到列表中
14 public void addUser(User user){
15 userMap.put (user.getId (),user.getUsername ());
16 }
17 //将用户移除列表
18 public void removeUser(User user){
19 userMap.remove (user.getId ());
20 }
21 //返回用户列表
22 public Map getOnlineUser() {
23 return userMap;
24 }
25 }（三）编写一个login.jsp页面，该页面输入用户的登录名和密码，完成用户登录功能
1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
2 <html>
3 <head>
4 <title>Title</title>
5 </head>
6 <body>
7 <center>
8 <h3>用户登录</h3>
9 </center>
10 <form action="${pageContext.request.contextPath}/LoginServlet" method="post">
11 <table border="1" width="550px" cellpadding="0" cellspacing="0" align="center">
12 <tr>
13 <td height="35" align="center">用户名</td>
14 <td>
15
16 <input type="text" name="username"/>
17 </td>
18 </tr>
19 <tr>
20 <td height="35" align="center">密 码</td>
21 <td>
22
23 <input type="password" name="password"/>
24 </td>
25 </tr>
26 <tr>
27 <td height="35" colspan="2" align="center">
28 <input type="submit" value="登录"/>
29
30 <input type="reset" name="重置"/>
31 </td>
32 </tr>
33 </table>
34 </form>
35 </body>
36 </html>（四）创建LoginServlet类，用于处理用户登录请求，如果用户登录成功就将该用户的信息封装到User中存入Session对象。
1 package servlet;
2
3 import entity.OnlineUser;
4 import entity.User;
5
6 import javax.servlet.ServletException;
7 import javax.servlet.annotation.WebServlet;
8 import javax.servlet.http.HttpServlet;
9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11 import java.io.IOException;
12 import java.util.Map;
13 import java.util.UUID;
14
15 @WebServlet(name = "LoginServlet",urlPatterns = "/LoginServlet")
16 public class LoginServlet extends HttpServlet {
17 protected void doPost(HttpServletRequest request, HttpServletResponse response)
18 throws ServletException, IOException {
19 request.setCharacterEncoding ("utf-8");
20 response.setContentType ("text/html;charset=utf-8");
21 String username = request.getParameter ("username");
22 String password = request.getParameter ("password");
23 if (username !=null && !username.trim ().equals ("")){
24 //登录成功
25 User user = new User ();
26 user.setId (UUID.randomUUID ().toString ());
27 user.setUsername (username);
28 user.setPassword (password);
29 request.getSession ().setAttribute ("user",user);
30 Map users = OnlineUser.getInstance ().getOnlineUser ();
31 request.setAttribute ("users",users);
32 request.getRequestDispatcher ("/showuser.jsp").forward (request,response);
33 } else {
34 request.setAttribute ("errorMsg","用户名或密码错误");
35 request.getRequestDispatcher ("/login.jsp").forward (request,response);
36 }
37 }
38
39 protected void doGet(HttpServletRequest request, HttpServletResponse response)
40 throws ServletException, IOException {
41 this.doPost (request,response);
42 }
43 }（五）编写一个showuser.jsp,该页面用于显示所有用户登录信息以及当前的登录的用户。
1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
2 <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
3 <html>
4 <head>
5 <title>Title</title>
6 </head>
7 <body>
8 <c:choose>
9 <c:when test="${sessionScope.user==null}">
10 <a href="${pageContext.request.contextPath}/login.jsp">登录</a>
11 <br/>
12 </c:when>
13 <c:otherwise>
14 欢迎你,${sessionScope.user.username}
15 <a href="${pageContext.request.contextPath}/LogoutServlet">退出</a>
16 </c:otherwise>
17 </c:choose>
18 <hr/>
19 在线用户列表
20 <br/>
21 <c:forEach var="user" items="${requestScope.users}">
22 ${user.value}
23 </c:forEach>
24 </body>
25 </html>（六）编写一个LogoutServlet类，用于注销用户登录信息，用户注销后跳转到showuser.jsp页面
1 package servlet;
2
3 import entity.OnlineUser;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.annotation.WebServlet;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10 import java.io.IOException;
11 import java.util.Map;
12
13 @WebServlet(name = "LogoutServlet",urlPatterns = "/LogoutServlet")
14 public class LogoutServlet extends HttpServlet {
15 protected void doPost(HttpServletRequest request, HttpServletResponse response)
16 throws ServletException, IOException {
17 request.setCharacterEncoding ("utf-8");
18 response.setContentType ("text/html;charset=utf-8");
19 request.getSession ().removeAttribute ("user");
20 Map users = OnlineUser.getInstance ().getOnlineUser ();
21 request.setAttribute ("users",users);
22 request.getRequestDispatcher ("/showuser.jsp").forward (request,response);
23 }
24 protected void doGet(HttpServletRequest request, HttpServletResponse response)
25 throws ServletException, IOException {
26 this.doPost (request,response);
27 }
28 }（七）使用不同浏览访问，呈现效果如下：
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