서비스 레이어 패턴

// UserService.java
@Service
@Transactional(readOnly = true) // 기본 읽기 전용
@RequiredArgsConstructor
public class UserService {
    private final UserRepository userRepository;
    private final PasswordEncoder passwordEncoder;

    public List<UserDto> findAll() {
        return userRepository.findAll().stream()
            .map(UserDto::from)  // Entity → DTO
            .collect(Collectors.toList());
    }

    public UserDto findById(Long id) {
        return userRepository.findById(id)
            .map(UserDto::from)
            .orElseThrow(() -> new UserNotFoundException(id));
    }

    @Transactional  // 쓰기는 별도 선언
    public UserDto create(CreateUserDto dto) {
        if (userRepository.existsByEmail(dto.getEmail())) {
            throw new DuplicateEmailException(dto.getEmail());
        }
        User user = User.builder()
            .email(dto.getEmail())
            .password(passwordEncoder.encode(dto.getPassword()))
            .name(dto.getName())
            .build();
        return UserDto.from(userRepository.save(user));
    }

    @Transactional
    public void delete(Long id) {
        User user = userRepository.findById(id)
            .orElseThrow(() -> new UserNotFoundException(id));
        userRepository.delete(user);
    }
}