title: Empty constructors and setters on JPA Entites
body: <p>I don't like the requirement on have at least one empty constructor and public setters on JPA entities. While I understand the issue on the EntityManager side, this invalidates class invariants.</p>
  
  <p>Does anyone have a solution for this (design pattern or idiom level) ?</p>
  
  <p>Thanks!</p>
  
  <p>Igor</p>