spring-boot-patterns

Spring Boot Patterns

Core patterns for building production-ready Spring Boot applications.

When to Use

• User is setting up a Spring Boot project
• User asks about @Component, @Service, @Repository usage
• User needs dependency injection patterns
• User is configuring profiles for dev/staging/prod
• User asks about externalized configuration or actuator

Core Patterns

Stereotype Annotations -- Layer Separation

Use the correct annotation for each architectural layer. Spring applies different behaviors to each.

@Repository  // Data access -- translates persistence exceptions
public class UserRepository {
    private final JdbcTemplate jdbc;
    public UserRepository(JdbcTemplate jdbc) { this.jdbc = jdbc; }

    public Optional<User> findById(Long id) {
        return jdbc.query("SELECT * FROM users WHERE id = ?",
            new BeanPropertyRowMapper<>(User.class), id).stream().findFirst();
    }
}

@Service  // Business logic -- transactional boundaries live here
public class UserService {
    private final UserRepository userRepository;
    public UserService(UserRepository userRepository) { this.userRepository = userRepository; }

    @Transactional
    public User createUser(CreateUserRequest request) {
        return userRepository.save(new User(request.name(), request.email()));
    }
}

@RestController  // Web layer -- handles HTTP requests
@RequestMapping("/api/v1/users")
public class UserController {
    private final UserService userService;
    public UserController(UserService userService) { this.userService = userService; }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public UserResponse createUser(@Valid @RequestBody CreateUserRequest request) {
        return UserResponse.from(userService.createUser(request));
    }
}

Constructor Injection

Always use constructor injection. It makes dependencies explicit, supports immutability, and works with final fields. Avoid field injection with @Autowired.

@Service
public class OrderService {
    private final OrderRepository orderRepository;
    private final PaymentGateway paymentGateway;
    private final NotificationService notificationService;

    // Single constructor -- @Autowired is implicit, no annotation needed
    public OrderService(
            OrderRepository orderRepository,
            PaymentGateway paymentGateway,
            NotificationService notificationService) {
        this.orderRepository = orderRepository;
        this.paymentGateway = paymentGateway;
        this.notificationService = notificationService;
    }
}