资料参考：
http://www.cnblogs.com/kenshincui/p/3871178.html
http://www.cnblogs.com/stoic/archive/2012/07/20/2601315.html
http://blog.csdn.net/wzzvictory/article/details/9674431?utm_source=tuicool
http://blog.csdn.net/kesalin/article/details/8194240
http://www.cnblogs.com/jay-dong/archive/2012/12/13/2815778.html