jsp 实现在线人数统计

首先写个类:
    import javax.servlet.*;
    import javax.servlet.http.*;
    public class SessionCounter implements HttpSessionListener {
    private static int activeSessions = 0;
    public void sessionCreated(HttpSessionEvent se) {
    activeSessions++;
    }
    public void sessionDestroyed(HttpSessionEvent se) {
    if(activeSessions > 0)
    activeSessions--;
    }
    public static int getActiveSessions() {
    return activeSessions;
    }
    }
    然后配置web.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <web-app version="2.4"
    xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    ****************************************
    <!-- Listeners -->
    <listener>
    <listener-class>
    SessionCount.SessionCounter (注意此处)
    </listener-class>
    </listener>
    *****************************************
    </web-app>