title: string id generator
body: <p>what's the easiest way to implement a string id in jpa ?
  So far what I have is</p>
  
  <pre><code>@Id
  @GeneratedValue
  private int id;
  </code></pre>
  
  <p>and what I'd like to have is something like</p>
  
  <pre><code>@Id
  @GeneratedValue
  private String id;
  </code></pre>
  
  <p>but if I use it like this, I get 'this id generator generates long, integer, short'.</p>