今天又重新學習了java web的基礎 監聽器技術，用sessionListener簡單的實現了網頁統計在線人數 （有一個bug就是當關閉網頁的時候 session不會關閉依舊存在，除非關閉服務器），代碼如下(前端網頁代碼就不顯示了):

LoginServlet.java:

 1 import javax.servlet.ServletException;
 2 import javax.servlet.annotation.WebServlet;
 3 import javax.servlet.http.HttpServlet;
 4 import javax.servlet.http.HttpServletRequest;
 
 5 import javax.servlet.http.HttpServletResponse;
 6 import javax.servlet.http.HttpSession;
 7 import java.io.IOException;
 8 
 9 @WebServlet(name = "LoginServlet",urlPatterns = "/login")
10 public class LoginServlet extends HttpServlet {
11     @Override
12     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws
 
 ServletException, IOException {
13        String username=request.getParameter("username");
14         HttpSession session=request.getSession();
15         session.setAttribute("username",username);
16         //重新定向到index.jsp
17         response.sendRedirect("index.jsp");
18     }
19 
20     @Override
 
21     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
22 
23     }
24 }

ExitServlet.java:

 1 package servlet;
 2 
 3 import javax.servlet.ServletException;
 4 import javax.servlet.annotation.WebServlet;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import javax.servlet.http.HttpSession;
 9 import java.io.IOException;
10 
11 @WebServlet(name = "ExitServlet",urlPatterns = "/exit")
12 public class ExitServlet extends HttpServlet {
13     @Override
14     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
15     //從session中移除loginName參數
16         response.getWriter().write("2222");
17         HttpSession session=request.getSession();
18         session.removeAttribute("username");
19         //重新定向到login.jsp
20         response.sendRedirect("login.jsp");
21     }
22 
23     @Override
24     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
25     doPost(request, response);
26     }
27 }

OnlineListener.java:

 1 package listener;
 2 
 3 import bean.User;
 4 
 5 import javax.servlet.ServletContextEvent;
 6 import javax.servlet.ServletContextListener;
 7 import javax.servlet.http.HttpSessionAttributeListener;
 8 import javax.servlet.http.HttpSessionEvent;
 9 import javax.servlet.http.HttpSessionListener;
10 import javax.servlet.http.HttpSessionBindingEvent;
11 
12 @javax.servlet.annotation.WebListener()
13 public class OnlineListener implements ServletContextListener,
14         HttpSessionListener, HttpSessionAttributeListener {
15     public OnlineListener() {
16     }
17     @Override
18     public void contextInitialized(ServletContextEvent sce) {
19      
20     }
21     @Override
22     public void contextDestroyed(ServletContextEvent sce) {
23     
24     }
25     @Override
26     public void sessionCreated(HttpSessionEvent se) {
27         System.out.println("會話已創建");
28     }
29     @Override
30     public void sessionDestroyed(HttpSessionEvent se) {
31         System.out.println("會話已銷毀");
32     }
33     
34     @Override
35     public void attributeAdded(HttpSessionBindingEvent sbe) {
36       //向session範圍中添加一個用戶
37         User.addUser(String.valueOf(sbe.getValue()));
38         System.out.println("session增加屬性為"+sbe.getName()+"值為："+sbe.getValue());
39     }
40     @Override
41     public void attributeRemoved(HttpSessionBindingEvent sbe) {
42      //將session會話中的用戶移除
43         User.removeUser(String.valueOf(sbe.getValue()));
44         System.out.println(sbe.getValue()+"屬性已被移除");
45     }
46     @Override
47     public void attributeReplaced(HttpSessionBindingEvent sbe) {
48       //獲取舊的屬性值
49         String oldValue=String.valueOf(sbe.getValue());
50         //獲取新的屬性值
51         String newValue=String.valueOf(sbe.getSession().getAttribute(sbe.getName()));
52         //移除舊的屬性，添加新的屬性
53         User.removeUser(oldValue);
54         User.addUser(newValue);
55     }
56 }

用兩個不同的瀏覽器運行結果如下圖所示：

項目工程目錄如下圖：

（堅持學習！努力加油！勉勵自己）

java web用監聽器listener簡單的實現在線統計人數