参考文章http://www.cnblogs.com/TankXiao/archive/2012/11/28/2793365.html http://www.infoq.com/cn/articles/etags http://405153947.iteye.com/blog/1913733 http://blog.csdn.net/eroswang/article/details/8302191
原文：http://www.cnblogs.com/lanse-yan/p/3569841.html