online.java

在网页中用与判断某用户是否已经在线的代码

package com.line;

import java.util.*;
import javax.servlet.*;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class OnLine implements HttpSessionBindingListener{
    private String username;
    private boolean mark=true;
    private Vector vc=new Vector();
    public void setUsername(String username){
    	this.username=username;
    }
	public void valueBound(HttpSessionBindingEvent se) {
		HttpSession session=se.getSession();
		ServletContext sct=session.getServletContext();
		vc=(Vector)sct.getAttribute("online");
		if(vc==null){
			vc=new Vector();
			vc.add(username);
		}
		else{
			if(vc.contains(username)){
				mark=false;
			}
			else{
				vc.add(username);
			}
		}
		sct.setAttribute("online",vc);
	}
	public void valueUnbound(HttpSessionBindingEvent se) {
		HttpSession session=se.getSession();
		ServletContext sct=session.getServletContext();
		vc=(Vector)sct.getAttribute("online");
		if(vc!=null){
			vc.removeElement(this.username);
		}
	}
	public boolean getMark(){
		return this.mark;
	}
}