都是别人总结的
http://www.cnblogs.com/eeeew/p/6495861.html
http://www.cnblogs.com/jinzy/p/6496103.html
http://www.cnblogs.com/niuyanan/p/6495678.html
http://www.cnblogs.com/hexiaozhen/p/6495898.html
http://www.cnblogs.com/changlel/p/6495623.html
原文：http://www.cnblogs.com/liuxiaoqian/p/6496333.html