参考文章:http://jingyan.baidu.com/article/11c17a2c7c0c69f446e39d06.html
http://www.cnblogs.com/zhangyongli2011/archive/2012/04/04/2431953.html
http://www.cnblogs.com/gaojun/archive/2012/11/22/2783257.html
http://blog.csdn.net/haoxiaoyan/article/details/53161920