title: Java EE: Where could I read about dao, services and why they're used?
body: <p>Ok
  I'm new at my job, and now I'm assigned to a project which uses Spring, Hibernate and Wicket.
  And I see a lot of DAO and Services packages and I want to understand why they're used and what is advantajes of this.</p>
  
  <p>I understand that DAO it's need for working with the databases, but I want more information.</p>
  
  <p>I need an overall, a BIG PICTURE of DAO and Services layers.</p>