HttpSessionAttributeListener 监听已登录用户信息

用户提出要求，需要知道哪些用户已经登录，但是在实际环境中，程序被部署到3台web上，前端用f5的负载均衡，那玩意没有玩过，幸好数据库是单一的，所以就简单建立了一个MySQL的内存表（Heap Table），来已经登录的用户信息。

package com.nbrc.lddw.util;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import com.nbrc.lddw.interceptor.AuthorizeInterceptor;
import com.nbrc.lddw.model.OnlineInfo;
import com.nbrc.lddw.model.User;
import com.nbrc.lddw.service.OnlineUserService;
/**
 * 
 * @author fox
 * @date 2009-02-09
 * @description 已登录用户的监听
 */
public class OnlineUserListener implements HttpSessionAttributeListener {
	private static Log log = LogFactory.getLog(OnlineUserListener.class);

	public void attributeAdded(HttpSessionBindingEvent hse) {
		log.info("value bound! make session info ...");
		HttpSession session = hse.getSession();		
		ApplicationContext context = 
			WebApplicationContextUtils.getRequiredWebApplicationContext(session.getServletContext());
		OnlineUserService svr = (OnlineUserService)context.getBean("onlineService");
		User u = null;
		if(session.getAttribute(AuthorizeInterceptor.USR_KEY)!=null)
			u = (User) session.getAttribute(AuthorizeInterceptor.USR_KEY);
		if(u!=null && svr.findByUserId(u.getId())==null){			
				OnlineInfo info = new OnlineInfo();
				info.setSessionId(session.getId());
				info.setUserId(u.getId());
				svr.save(info);
		}else{
				log.error("can't get user in session");
		}		
	}

	public void attributeRemoved(HttpSessionBindingEvent hse) {
		HttpSession session = hse.getSession();
		ApplicationContext context = WebApplicationContextUtils.getRequiredWebApplicationContext(session.getServletContext());
		OnlineUserService svr = (OnlineUserService)context.getBean("onlineService");
		if(svr.findById(session.getId())!=null){
			svr.removeById(session.getId());				
		}
	}

	public void attributeReplaced(HttpSessionBindingEvent se) {
		// TODO Auto-generated method stub
		
	}
	

}

不过这里还有一个bug，当用户关闭浏览器的时候，还需要将Session里面的内容清除，显示的才是正确的内容。