Do I really need a service layer?

Question

My web application is written using Spring MVC + Hibernate.

• My model is "Customer" entity POJO.
• I have got a DAO object "CustomerDAO", its method "saveCustomer(c)" contains the code interacting with Hibernate;
• Then I created a "CustomerService with a "saveCustomer(c)" method who simply pass the customer object to the dao for saving;
• Finally there are "CustomerController" and customer.jsp, who are responsible for the view layer, the jsp's form fields are bound to a Customer object on the controller side. The controller calls the service.

I saw a lot of applications follow this (best) practice but I'm wondering why I would need a service layer.

Maybe it's useful for decoupling purpose: I can show a universal facade to the controllers and inject into the service HibernateDAO, GaeDAO, MyDAO, and so on.... But I could do that without the service, too: using an interface.

I also tought: validation. I'll make my Customer validation in the service but.... it's much more convenient to validate in Spring controller.

Help me understand the concept please :)

Answer 1

You don't need a service layer. However it helps you to

• Decouple your components
• You can enforce specific business rules in your service layer which should be agnostic to your repository
• Let a service facade one or more repositories. Let's consider the following sample

class Service {   private DatabaseBarRepo barRepo;   private DatabaseFooRepo fooRepo;    @Transactional   public void serviceRoutine() {      barRepo.doStuff();      fooRepo.doStuff();   } } 

Here we let two separate repositories take part in the same transaction. This is specific for databases albeit the principles are valid for other systems as well.