JAVA 获取在线用户数的方法

在互联网的应用中，通常需要统计当前时间使用系统的人数，用来衡量网络的使用量以及稳定性的数据，如何实现这种功能呢，其实通过 java servlet listener 就可以实现，下面是实现的方法.
1. 编写 扩展实现 HttpSessionListener 接口.
2. 在web.xml 中配置listener.

第一步，编写如下扩展

import javax.servlet.http.HttpServlet;   
import javax.servlet.http.HttpSessionAttributeListener;   
import javax.servlet.http.HttpSessionBindingEvent;   
import javax.servlet.http.HttpSessionBindingListener;   
import javax.servlet.http.HttpSessionEvent;   
import javax.servlet.http.HttpSessionListener;   
  
public class OnlineCounter extends HttpServlet implements HttpSessionListener,   
    HttpSessionAttributeListener,HttpSessionBindingListener {   
  public OnlineCounter(){   
    System.out.println("OnlineCounter initialized.");   
  }   
  private static final long serialVersionUID = 1L;   
  
  private static int sessionCounter = 0;   
  
  private static int attributeCounter = 0;   
  
  public void sessionCreated(HttpSessionEvent se) {   
    sessionCounter++;   
    System.out.println("session created");   
  }   
  
  public void sessionDestroyed(HttpSessionEvent se) {   
    sessionCounter--;   
    System.out.println("session destroied");   
  }   
  
  public void attributeAdded(HttpSessionBindingEvent se) {   
    attributeCounter++;   
    System.out.println("attribute added");   
  }   
  
  public void attributeRemoved(HttpSessionBindingEvent se) {   
    attributeCounter--;   
    System.out.println("attribute removed");   
  }   
  
  public void attributeReplaced(HttpSessionBindingEvent se) {   
    System.out.println(se.getName()+" replaced");   
  }   
     
  public void valueBound(HttpSessionBindingEvent event){   
      System.out.println(event.getName()+"_Bound_"+event.getValue());   
  }   
  
  public void valueUnbound(HttpSessionBindingEvent event) {   
    System.out.println(event.getName()+"_Unbound_"+event.getValue());   
  }   
  
  public static int getOnlineSession() {   
    return sessionCounter;   
  }   
  public static int getOnlineAttribute() {   
    return attributeCounter;   
  }   
}   

com.yihaomen.OnlineCounter