userlistener.java

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package login;

import javax.servlet.http.*;

public class UserListener
    implements HttpSessionAttributeListener {
  /**
   * Notification that an attribute has been added to a session.
   *
   * @param se HttpSessionBindingEvent
   * @todo Implement this javax.servlet.http.HttpSessionAttributeListener
   *   method
   */
  int users=0; //当前用户数
  public void attributeAdded(HttpSessionBindingEvent se) {
    if(se.getName().equals("username"))
      {
        users++;
        System.out.println("用户登录，用户名："+se.getValue());
        System.out.println("当前用户数："+users);
      }
  }

  /**
   * Notification that an attribute has been removed from a session.
   *
   * @param se HttpSessionBindingEvent
   * @todo Implement this javax.servlet.http.HttpSessionAttributeListener
   *   method
   */
  public void attributeRemoved(HttpSessionBindingEvent se) {
    if(se.getName().equals("username"))
  {
    users--;
    System.out.println("用户注销，用户名："+se.getValue());
    System.out.println("当前用户数："+users);
  }

  }

  /**
   * Notification that an attribute has been replaced in a session.
   *
   * @param se HttpSessionBindingEvent
   * @todo Implement this javax.servlet.http.HttpSessionAttributeListener
   *   method
   */
  public void attributeReplaced(HttpSessionBindingEvent se) {
  }
}