Spring Boot Patterns

Layered Architecture

src/main/java/com/example/app/
  config/          # @Configuration beans
  controller/      # @RestController (thin, delegates to service)
  service/         # @Service (business logic)
  repository/      # @Repository (data access via JPA)
  model/
    entity/        # @Entity JPA classes
    dto/           # Request/response DTOs
    mapper/        # MapStruct or manual mapping
  exception/       # @ControllerAdvice, custom exceptions
  security/        # SecurityFilterChain, JWT filters

Controllers handle HTTP concerns. Services contain business logic. Repositories handle persistence.