Event monitoring: Number of logged-on users (including user names)

Event monitoring: Number of logged-on users (including user names)

(1) create a User class to encapsulate a User information. This class implements the valueBound () method in the HttpSessionBindingListener interface.
And valueUnbound () method

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 @ Override38 public void valueBound (HttpSessionBindingEvent event) {39 // Save the user to the list of 40 onlineusers. getInstance (). addUser (this); 41} 42 43 @ Override44 public void valueUnbound (HttpSessionBindingEvent event) {45 OnlineUser. getInstance (). removeUser (this); 46} 47}

(2) create an OnlineUser class to store and obtain the list of users. This list should be the same for all pages, so it is a singleton mode.

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 // Add the User to the list 14 public void addUser (user User) {15 userMap. put (user. getId (), user. getUsername (); 16} 17 // Remove User List 18 public void removeUser (user User) {19 userMap. remove (user. getId (); 20} 21 // return to user list 22 public Map getOnlineUser () {23 return userMap; 24} 25}

(3) Compile a login. jsp page. Enter the user's logon name and password to complete the user logon function.

1 <% @ page contentType = "text/html; charset = UTF-8 "language =" java "%> 2 
(4) create a LoginServlet class to process User login requests. If the User logs on successfully, the User information is encapsulated into the User and saved to the Session object.
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. g EtParameter ("password"); 23 if (username! = Null &&! Username. trim (). equals ("") {24 // login successful 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", "incorrect user name or password"); 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}
(5) Compile a showuser. jsp page to display the logon information of all users and the current logon users.
1 <% @ page contentType = "text/html; charset = UTF-8 "language =" java "%> 2 <% @ taglib prefix =" c "uri =" http://java.sun.com/jsp/jstl/core "%> 3 
(6) Compile a LogoutServlet class to log out of user logon information. After logging out, the user will jump to the showuser. jsp page.
 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 }
(7) use different browser accesses to display the following results: