1 http://www.cnblogs.com/noTice520/archive/2012/02/10/2345057.html
2 http://www.92coding.com/blog/index.php/archives/288.html
3 http://www.kwstu.com/ArticleView/kwstu_201332113621629
备注：1，2代码相同。不知道谁借鉴谁，不过2讲的更详细些