The Service layer
So far so good, we have created a Presentation layer that contains a controller, a dispatcher servlet, view resolvers, and more. And then we created the Domain layer, which contains a single domain class
Product. Finally, we created the Persistence layer, which contains a repository interface and an implementation to access our
Product domain objects from an in-memory database.
But we are still missing one more concept called the Service layer. Why do we need the Service layer? We have seen a Persistence layer dealing with all data access (CRUD) related logic, a Presentation layer dealing with all web requests and view-related activities, and a Domain layer containing classes to hold information that is retrieved from database ...