So far, we have seen how to organize our code into layers so that we can avoid tight coupling between various code files, and improve reusability and the separation of concerns. We just created one domain class, one repository class, and one service class for demonstration purposes, but a typical, real-world MVC application may contain as many domain, repository, and service classes as required. Each layer is usually connected through interfaces and always controller access domain objects from the repository via the service interface only.

Every typical, enterprise-level Spring MVC application will logically have four layers: presentation, domains, persistence, and services. The domain layer is sometimes called the model layer. The following block diagram will help you conceptualize this idea:

The layers of a Spring MVC application

So, we learned how to create a service layer object and repository layer object; what we saw in the service layer...