Session监听器

通过实现session监听器，将退出的用户从列表中删除
在web.xml进行如下配置

<listener>
<listener-class>cn.com.Demo.Listener.MyListener</listener-class>>
</listener>>

然后代码如下

public class MyListener implements HttpSessionListener,
        HttpSessionActivationListener {

    @Override
    public void sessionDidActivate(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void sessionWillPassivate(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void sessionCreated(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("Create session"+arg0.getSession().getId());
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("destroyed session"+arg0.getSession().getId());
        HttpSession session = arg0.getSession();
        String userName = (String)session.getAttribute("LOGIN_USER");
        ServletContext ctx = session.getServletContext();
        Set<String> userSet = (Set<String>)ctx.getAttribute("USER_SET");
        if(userSet!=null)
        {
            userSet.remove(userName);
        }
    }

}