MavenprojectJPA:PersistvsMerge -> http://www.17cats.com/newblog/post/16d09bee/?tsx=tgO0az8UW1aNzsf9&t=69svxBstk2sWUqbY&bx=165827707&query=0vHfcGpO0641d63i&aim=gonXFNbHteXAWNaX