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.

REST Controller

@RestController
@RequestMapping("/api/v1/orders")
@RequiredArgsConstructor
public class OrderController {

    private final OrderService orderService;

    @GetMapping
    public Page<OrderResponse> list(
            @RequestParam(defaultValue = "0") int page,
            @RequestParam(defaultValue = "20") int size) {
        return orderService.findAll(PageRequest.of(page, size));
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public OrderResponse create(@Valid @RequestBody CreateOrderRequest request) {
        return orderService.create(request);
    }

    @GetMapping("/{id}")
    public OrderResponse getById(@PathVariable UUID id) {
        return orderService.findById(id);
    }
}

JPA Entity and Repository

@Entity
@Table(name = "orders")
@Getter @Setter @NoArgsConstructor
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private UUID id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "customer_id", nullable = false)
    private Customer customer;

    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<OrderItem> items = new ArrayList<>();

    @Enumerated(EnumType.STRING)
    private OrderStatus status = OrderStatus.PENDING;