refurl:http://enetq.blog.51cto.com/479739/702256
http://www.mkyong.com/servlet/a-simple-httpsessionlistener-example-active-sessions-counter/
http://chenjianjx.iteye.com/blog/1135580 SessionMap让sesson失效。
http://www.blogjava.net/persister/archive/2006/12/30/90977.html session监控
http://blog.csdn.net/zyujie/article/details/8717898 用过滤器判断session是否失效。
http://www.fanli7.net/a/caozuoxitong/OS/20101005/32631.html
http://hi.baidu.com/harbin_sakura/item/225fdfb974dce2eb4fc7fda7