参考:http://www.cnblogs.com/tdyizhen1314/archive/2012/10/25/2739957.html
http://baike.baidu.com/link?url=nLMjpCzomdE9CpdBiHIJazXj5kW4wNVWpJoUILqyEQ7h4_Gv5pjiyxztGCDViivoLOiZPP6lLelzpLZXYlvrczLJ_RL3ZiAQ1HG-Q43RzRdS7dd1mPMmr0KTwwEMcZMlJ2lhbZfY1-lcSl3nk6rJ1qPgCqvAfZZuWQK-MLJVci3