javaweb 监听器

public class OnlineCountListener implements HttpSessionListener {
//创建Session监听：看你的一举一动
    //一旦创建Session就会触发一次这个事件
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        ServletContext sc = httpSessionEvent.getSession().getServletContext();
        Integer oc = (Integer) sc.getAttribute("OnlineCount");
        if(oc==null){
            oc = new Integer(1);
        }else{
            int count =oc.intValue();
            oc = new Integer(count+1);
        }
        sc.setAttribute("OnlineCount",oc);
    }
    //销毁Session监听
    //一旦销毁Session就会触发一次这个事件
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext sc = httpSessionEvent.getSession().getServletContext();
        Integer oc = (Integer) sc.getAttribute("OnlineCount");
        if(oc==null){
            oc = new Integer(0);
        }else{
            int count =oc.intValue();
            oc = new Integer(count-1);
        }
        sc.setAttribute("OnlineCount",oc);
        /*
        Session销毁的方案
        1.手动销毁
        2.自动销毁
         */
    }
}

<!--    注册监听器-->
    <listener>
        <listener-class>com.kuang.listener.OnlineCountListener</listener-class>
    </listener>