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

posted @ 2024-04-21 12:22 文采杰出阅读(72) 评论(0) 编辑收藏举报

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	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;
	}
	}

	<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>

	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);
	}
	}

	<%@ 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>