參考
https://www.cnblogs.com/weidagang2046/archive/2011/06/04/idempotence.html
https://segmentfault.com/a/1190000017212260
http://dingdingblog.com/article/21
參考
https://www.cnblogs.com/weidagang2046/archive/2011/06/04/idempotence.html
https://segmentfault.com/a/1190000017212260
http://dingdingblog.com/article/21