以下三篇不错的介绍~~~ http://www.cnblogs.com/kzang/articles/2751424.html#a3 http://www.cnblogs.com/shiyangxt/archive/2008/09/11/1289493.html http://www.cnblogs.com/biyeymyhjob/archive/2012/07/22/2603525.html