title: How to Tell JPA the prefered DataType
body: <p>If I use JPA (EclipseLink) to create tables a String type results in a varchar2(255). How could I tell JPA (via Annotation) to create a varchar2(20) attribute. </p>
  
  <p>If I have a List JPA creates a BLOB(4000) but I would like a varchar2 (my serialized object's string is short)</p>
  
  <p>How is this possible? Do I have to do it by hand?</p>