监听器

监听器有very many的多，这里就用监听实时的在线人数来介绍-

• 实现监听器的接口

public void sessionCreated(HttpSessionEvent se) {
        ServletContext gsc = se.getSession().getServletContext();
        Integer onlineperson = (Integer) gsc.getAttribute("onlineperson");
        if(onlineperson==null){
            onlineperson=new Integer(1);
        }else{
            int count = onlineperson.intValue();
            onlineperson=new Integer(count+1);
        }
        gsc.setAttribute("onlineperson",onlineperson);
    }

    @Override
    //销毁session监听
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext gsc = se.getSession().getServletContext();
        Integer onlineperson = (Integer) gsc.getAttribute("onlineperson");
        if(onlineperson==null){
            onlineperson=new Integer(1);
        }else{
            int count = onlineperson.intValue();
            onlineperson=new Integer(count-1);
        }
        gsc.setAttribute("onlineperson",onlineperson);

• 配置xml

<listener>
        <listener-class>com.Google.OnlineLisetener</listener-class>
    </listener>