Understanding Service and DAO layers

Question

I was asked to create documentation of classes in the business logic module of a project. I noticed that there was a pattern on how the classes where created. The pattern looks like this

    public class AModel(){
          //fields
          //getter and setters
    }

    public class AService(){

          public void processA(AModel model){
                  //creates instance of AModel, assigns values to fields
                  //calls ADaoService methods
          }  

    }

    public class ADaoService(){

           //has methods which call ADao methods
           //sample
           public AModel retrieveById(long id){
                 log.debug(...);
                 return (ADao.retrieveById(id));
           }

    }

    public class ADAo(){
            //has entityManager and some query

            public AModel retrieveById(long id){
                  return((AModel) entityManager.find(AModel.class, id));
            }
    }

What I don't understand is why does AService calls ADaoService methods instead of just calling ADao methods since ADaoService methods are just calling ADao methods. It seems to me that ADaoService was just a waste of code. They are usign Hibernate and JBoss server. I'm just new to this type of architecture. Hope someone can help me understand. Thanks.

Answer 1

Well, if ADaoService is doing nothing but delegating calls to ADao then clearly you're right - it has no existence justification at the moment.

Regarding future justifications, well, AFAIK, the typical layering does not include ADaoService layer. Where I work we don't have it. Never seen it in Hibernate docs...

Either your architects were generous with layers or they had some non-typical scenario in mind.

If there's no current usages of the layer and no clear future usages - you're better off without it.