参考这几篇博客:
1:http://www.cnblogs.com/realh/archive/2010/10/04/1841907.html
2:http://www.cnblogs.com/min0208/archive/2012/05/24/2515584.html
3:http://berdy.iteye.com/blog/1106731
4:http://blog.csdn.net/wklken/article/details/7253245