spring-boot-engineer Checked

public ProductService(ProductRepository repo) { // constructor injection — no @Autowired

this.repo = repo;

}

@Transactional(readOnly = true)

public List<Product> search(String name) {

return repo.findByNameContainingIgnoreCase(name);

}

@Transactional

public Product create(ProductRequest request) {

var product = new Product();

product.setName(request.name());

product.setPrice(request.price());

return repo.save(product);

}

}

### REST Controller

@RestController

@RequestMapping("/api/v1/products")

@Validated

public class ProductController {

private final ProductService service;

public ProductController(ProductService service) {

this.service = service;

}

@GetMapping

public List<Product> search(@RequestParam(defaultValue = "") String name) {

return service.search(name);

}

@PostMapping

@ResponseStatus(HttpStatus.CREATED)

public Product create(@Valid @RequestBody ProductRequest request) {

return service.create(request);

}

}

### DTO (record)

public record ProductRequest(

@NotBlank String name,

@DecimalMin("0.0") BigDecimal price

) {}

### Global Exception Handler

@RestControllerAdvice

public class GlobalExceptionHandler {

@ExceptionHandler(MethodArgumentNotValidException.class)

@ResponseStatus(HttpStatus.BAD_REQUEST)

public Map<String, String> handleValidation(MethodArgumentNotValidException ex) {

return ex.getBindingResult().getFieldErrors().stream()

.collect(Collectors.toMap(FieldError::getField, FieldError::getDefaultMessage));

}

@ExceptionHandler(EntityNotFoundException.class)

@ResponseStatus(HttpStatus.NOT_FOUND)

public Map<String, String> handleNotFound(EntityNotFoundException ex) {

return Map.of("error", ex.getMessage());

}

}

### Test Slice

@WebMvcTest(ProductController.class)

class ProductControllerTest {

@Autowired MockMvc mockMvc;

@MockBean ProductService service;

@Test

void createProduct_validRequest_returns201() throws Exception {

var product = new Product(); product.setName("Widget"); product.setPrice(BigDecimal.TEN);

when(service.create(any())).thenReturn(product);

mockMvc.perform(post("/api/v1/products")

.contentType(MediaType.APPLICATION_JSON)

.content("""{"name":"Widget","price":10.0}"""))

.andExpect(status().isCreated())

.andExpect(jsonPath("$.name").value("Widget"));

}

}

## Constraints

### MUST DO

| Rule | Correct Pattern |
|------|----------------|
| Constructor injection | `public MyService(Dep dep) { this.dep = dep; }` |
| Validate API input | `@Valid @RequestBody MyRequest req` on every mutating endpoint |
| Type-safe config | `@ConfigurationProperties(prefix = "app")` bound to a record/class |
| Appropriate stereotype | `@Service` for business logic, `@Repository` for data, `@RestController` for HTTP |
| Transaction scope | `@Transactional` on multi-step writes; `@Transactional(readOnly = true)` on reads |
| Hide internals | Catch domain exceptions in `@RestControllerAdvice`; return problem details, not stack traces |
| Externalize secrets | Use environment variables or Spring Cloud Config — never `application.properties` |

### MUST NOT DO
- Use field injection (`@Autowired` on fields)
- Skip input validation on API endpoints
- Use `@Component` when `@Service`/`@Repository`/`@Controller` applies
- Mix blocking and reactive code (e.g., calling `.block()` inside a WebFlux chain)
- Store secrets or credentials in `application.properties`/`application.yml`
- Hardcode URLs, credentials, or environment-specific values
- Use deprecated Spring Boot 2.x patterns (e.g., `WebSecurityConfigurerAdapter`)

[Documentation](https://jeffallan.github.io/claude-skills/skills/backend/spring-boot-engineer/)