Javaweb监听器

package jiantingqi;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListener implements HttpSessionListener {

private static int online=0;
public void sessionCreated(HttpSessionEvent arg0) {
System.out.println("新增用户");
//用户登录在线人数加1
++online;
System.out.println("online="+online);
}

public void sessionDestroyed(HttpSessionEvent arg0) {
System.out.println("用户退出");
//用户退出在线人数减1
online--;
System.out.println("online="+online);

}

}