spring-boot-fallback

Spring Boot Fallback

Overview

Quarkus is the default (see quarkus-service-architecture). Spring Boot is the fallback — reach for it only when Quarkus genuinely does not fit. The architecture is the same clean layering; only the annotations and container differ.

Core principle: Same layered design as Quarkus. Spring is a container choice, not a license to sprawl.

When Spring Boot instead of Quarkus

• The repository already uses Spring Boot — follow it.
• A required library/integration has no Quarkus extension and no clean CDI alternative.
• The deployment target or team standard mandates Spring.

If none of these hold, use Quarkus.

Layer mapping (same responsibilities, Spring surface)

Layer	Quarkus	Spring Boot
Resource/Controller	JAX-RS @Path	@RestController @RequestMapping
Service	@ApplicationScoped	@Service
Repository	Panache	JpaRepository (Spring Data)
Validation	@Valid + Bean Validation	@Valid + Bean Validation
Config	@ConfigProperty	@ConfigurationProperties / @Value
Transaction	@Transactional (service)	@Transactional (service)

Patterns (identical discipline)

• Constructor injection only — Spring injects a single constructor automatically; no @Autowired on fields.
• DTOs (records) at the controller edge; never return JPA entities from a controller.
• Bean Validation on request DTOs, @Valid on the controller method.
• Domain invariants live in the domain class, not only in the DTO annotations.
• Global error handling via @RestControllerAdvice mapping domain exceptions to status codes — controllers stay thin.

Worked Example

@RestController
@RequestMapping("/tasks")
class TaskController {
    private final TaskService service;
    TaskController(TaskService service) { this.service = service; }   // constructor injection

    @PostMapping
    ResponseEntity<TaskResponse> create(@Valid @RequestBody CreateTaskRequest req) {
        Task t = service.create(req.title());
        return ResponseEntity.status(201).body(TaskResponse.from(t));
    }
}

@Service
class TaskService {
    private final TaskRepository repo;
    TaskService(TaskRepository repo) { this.repo = repo; }

    @Transactional
    Task create(String title) {
        Task t = Task.create(title);   // domain enforces invariants
        return repo.save(t);
    }
}