There is a example of REST API POST PUT GET DELETE with layers . Entity class is inside of model package. Controller package has Controller Class who directs to endpoints. Repository Class is an abstract class .It extends JPARepository for using Database Operations. It facilitates these operations(CRUD). Service -> It provides Business Logic in this Layer. With Postman U can test Inside of Get I harcoded something else to test the connections.I am working on it. I am learning every day different things.