Java EE: Where could I read about dao, services and why they're used?

Question

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.

I understand that DAO it's need for working with the databases, but I want more information.

I need an overall, a BIG PICTURE of DAO and Services layers.

Answer 1

Take a look at Spring in Action. This book explains all essential aspects of Spring, DAOs and services.

Answer 2

• DAO at Wiki
• Also look at N-tier
• Information system's commons layers

Answer 3

Best place to learn Spring. Of course its awesome official tutorial.

Choose the version you are working with, otherwise you might end no finding some features in your environment. The link provided is of Spring 3.0