title: Why use a service layer instead of a helper class for spring controllers?
body: <p>In my experience this is how ive seen spring controllers used : 
  Define a spring controller which returns a value of some type to presentation layer.
  The controller request mapping method calls a service layer. The service layer itself consists of an interface and implementation. The service interface always contains just one method so its not really polymorphic as it keeps 'one form' consistently. The service implementation may access data of some kind, perhaps from a DAO and returns it the controller. The controller may amend this data slightly before returning its returned to the presentation layer.</p>
  
  <p>What is this point of having an interface in this case ? Ive never encountered a spring service implementation called from multiple controllers, so why the interface ?</p>
  
  <p>Does it not make more sense to use a helper controller class which performs the actions of the service implementation ?</p>