package com.test;

import javax.servlet.http.*;
import javax.servlet.*;

public class OnLineCountListener implements HttpSessionListener,ServletContextListener,ServletContextAttributeListener
{
	private int count;
	private ServletContext context = null;

	public OnLineCountListener()
	{
		count = 0;
		//setContext();
	}
	
	//創(chuàng)建一個session時激發(fā)
	public void sessionCreated(HttpSessionEvent se)
	{
		count++;
		setContext(se);
	}

	//一個session失效時激發(fā)
	public void sessionDestroyed(HttpSessionEvent se)
	{
		count--;
		setContext(se);
	}

	//設(shè)置context的屬性，它將激發(fā)attibuteReplaced或attibuteAdded方法
	public void setContext(HttpSessionEvent se)
	{
		se.getSession().getServletContext().setAttribute("onLine",new Integer(count));
	}

	//增加一個新的屬性時激發(fā)
	public void attributeAdded(ServletContextAttributeEvent event)
	{
		log("attributeAdded("+event.getName()+"','"+event.getValue()+")");
	}

	//刪除一個屬性時激發(fā)
	public void attributeRemoved(ServletContextAttributeEvent event)
	{
		log("attributeRemoved("+event.getName()+"','"+event.getValue()+")");
	}

	//替換一個屬性時激發(fā)
	public void attributeReplaced(ServletContextAttributeEvent event)
	{
		log("attributeReplaced("+event.getName()+"','"+event.getValue()+")");
	}

	//context刪除時激發(fā)
	public void contextDestroyed(ServletContextEvent event)
	{
		log("contextDestroyed()");
		this.context = null;
	}

	//context初始化時激發(fā)
	public void contextInitialized(ServletContextEvent event)
	{
		log("contextInitialized()");
		this.context = event.getServletContext();
	}

	public void log(String message)
	{
		System.out.println("ContextListener:"+message);
	}
};