Servlet监听器统计在线人数
- 首先，我们需要创建一个HttpSessionListener来监听会话的创建和销毁事件。当新的会话创建时，我们将增加在线人数；当会话销毁时，我们将减少在线人数。
public class OnlineCounterListener implements HttpSessionListener {
private static int activeSessions = 0;
@Override
public void sessionCreated(HttpSessionEvent se) {
// HttpSessionListener.super.sessionCreated(se);
activeSessions++;
System.out.println("Session created. Active sessions: " + activeSessions);
}
@Override
public void sessionDestroyed(HttpSessionEvent se) {
// HttpSessionListener.super.sessionDestroyed(se);
if (activeSessions > 0) {
activeSessions--;
System.out.println("Session destroyed. Active sessions: " + activeSessions);
}
}
public static int getActiveSessions(){
return activeSessions;
}
}
- 接下来，我们需要在web.xml文件中配置该监听器，每当有新的用户访问应用程序时，都会创建一个新的会话，从而触发sessionCreated方法，增加在线人数。当会话过期或用户关闭浏览器时，会触发sessionDestroyed方法，减少在线人数。
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<listener>
<listener-class>com.example.OnlineCounterListener</listener-class>
</listener>
<!-- Servlet and JSP configurations would go here -->
</web-app>
- 创建一个Servlet和JSP页面来显示在线人数：
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/online-count")
public class OnlineCountServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
int activeUsers = OnlineCounterListener.getActiveSessions();
request.setAttribute("activeUsers", activeUsers);
request.getRequestDispatcher("/online-count.jsp").forward(request, response);
}
}
- JSP示例 (在webapp文件夹下新建online-count.jsp):
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Online User Count</title>
</head>
<%
session.setMaxInactiveInterval(10);// 设置session有效时间
%>
<body>
<h1>Currently Online: ${activeUsers}</h1>
</body>
</html>
启动tomcat,浏览器访问http://localhost:8080/自定义应用程序上下文/online-count,
输出结果: Currently Online: 2
