参考:
http://www.hqew.com/tech/doc/482753.html
http://www.cnblogs.com/Hello-Walker/archive/2012/06/11/2545409.html
http://wenku.baidu.com/link?url=o-X-PQRJ96g4duHO33q4_uJoiW2EE69oUp2eZnuL26UNrrNfnQ1YFwCsYewADKxNQtYaKt_elwI2n1FMiWlxi_o54_l-0f-3oqhfRAK2kTy