Spring Boot Application: Layers

 In general, there are following three layers in a Spring Boot application, or in any modern web application for that matter.

1. Controller

  - It is responsible for the interaction with the clients and handles all the requests coming into the solution and responses going out of it.

2. Service

  - This layer sits between the controller and repository layer and acts as a liaison / mediator between them and it is in this layer that all the core business logics are implemented.

  - At some places, this layer is further broken down into two sub-layers:

      a. Service (Interface layer)

      b. Service Implementation (Implementing Class layer)

3. Repository

  - It is the layer that is responsible for the interaction with the database system in the back-end. It sole purpose is to create/read/update/delete (CRUD) data to/from the database.

  - It is also known as DAO (Data Access Object) in some solutions.

  - Just like in service, at some places, this layer is further broken down into two sub-layers:

      a. Repository (Interface layer)

      b. Repository Implementation (Implementing Class layer)