SKILL.md
Critical Patterns
Constructor Injection (REQUIRED)
// ✅ ALWAYS: Constructor injection for testability
@Service
public class OrderService {
private final OrderRepository repository;
private final PaymentService paymentService;
public OrderService(OrderRepository repository, PaymentService paymentService) {
this.repository = repository;
this.paymentService = paymentService;
}
}
// ❌ NEVER: Field injection
@Service
public class OrderService {
@Autowired
private OrderRepository repository;
}
Records for DTOs (REQUIRED)
// ✅ ALWAYS: Use records for immutable DTOs
public record UserDTO(
String id,
String name,
String email
) {}
// ❌ NEVER: Mutable POJOs for data transfer
public class UserDTO {
private String id;
// ... getters, setters, equals, hashCode
}
Exception Handling (REQUIRED)
// ✅ ALWAYS: Use @ControllerAdvice
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<ErrorResponse> handleNotFound(ResourceNotFoundException ex) {
return ResponseEntity.status(HttpStatus.NOT_FOUND)
.body(new ErrorResponse(ex.getMessage()));
}
}
Decision Tree
Need REST API? → Use @RestController
Need data validation? → Use @Valid + Bean Validation
Need database access? → Use Spring Data JPA
Need async processing? → Use @Async
Need caching? → Use @Cacheable
Need config properties? → Use @ConfigurationProperties
Code Examples
REST Controller
@RestController
@RequestMapping("/api/users")
public class UserController {
private final UserService userService;
public UserController(UserService userService) {
this.userService = userService;
}
@GetMapping("/{id}")
public ResponseEntity<UserDTO> getUser(@PathVariable String id) {
return userService.findById(id)
.map(ResponseEntity::ok)
.orElse(ResponseEntity.notFound().build());
}
@PostMapping
public ResponseEntity<UserDTO> createUser(@Valid @RequestBody CreateUserRequest request) {
UserDTO created = userService.create(request);
return ResponseEntity.status(HttpStatus.CREATED).body(created);
}
}
Bean Validation
public record CreateUserRequest(
@NotBlank(message = "Name is required")
String name,
@Email(message = "Invalid email format")
@NotBlank
String email,
@Size(min = 8, message = "Password must be at least 8 characters")
String password
) {}
Commands
mvn clean install # Build project
mvn spring-boot:run # Run application
mvn test # Run tests
mvn dependency:tree # View dependencies
./mvnw spring-boot:run # Run with wrapper
Resources
