先贴几个链接
http://blog.csdn.net/goodelephant/article/details/24769421
http://blog.csdn.net/gaofang2009/article/details/6073029
http://www.cnblogs.com/zhaozhan/archive/2011/01/09/1931340.html
http://blog.csdn.net/ximen502/article/details/9120233
http://www.cnblogs.com/yylp521/p/3148856.html
http://blog.csdn.net/goodelephant/article/details/24769421