MavenprojectJPA:PersistvsMerge -> http://www.17cats.com/newblog/tags/%E6%9D%8E%E5%BF%A0%E6%B5%A9/?nex=u86rLnaBvngT2pe0&date=39be01e9-1e8a-4544-a14b-1ec2d3f17817&bx=0.3629258392558087