【JavaEE企业应用实战学习记录】sessionListener

package sanglp.servlet;


import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import java.util.Hashtable;
import java.util.Map;

/**
 * Created by Administrator on 2016/10/6.
 */
@WebListener
public class HttpSessionListener implements javax.servlet.http.HttpSessionListener {

    //当用户与服务之间开始session时触发该方法
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        HttpSession session=httpSessionEvent.getSession();
        ServletContext application=session.getServletContext();
        //获取sessionId
        String sessionId=session.getId();
        //如果是一次新的会话
        if(session.isNew()){
            String user=(String)session.getAttribute("user");
            //未登陆用户当游客处理
            user=(user==null)?"游客":user;
            Map<String,String> online=(Map<String, String>) application.getAttribute("online");
            if(online==null){
                online=new Hashtable<String,String>();
                //将用户在线信息放入Map中
                online.put(sessionId,user);
                application.setAttribute("online",online);
            }
        }
    }

    //当用户与服务器之间session断开时触发该方法
    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
    HttpSession session=httpSessionEvent.getSession();
        ServletContext application=session.getServletContext();
        String sessionId=session.getId();
        Map<String,String> online=(Map<String,String>)application.getAttribute("online");
        if(online!=null){
            //删除该用户的在线信息
            online.remove(sessionId);
        }
        application.setAttribute("online",online);
    }
}