ServiceDemo

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public UserDTO createUser(UserDTO userDTO) {
        User user = new User();
        // 将UserDTO的属性设置到User对象中
        // ...
        userRepository.save(user);
        return userDTO;
    }

}

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public void deleteUser(Long id) {
        User user = userRepository.findById(id).orElse(null);
        if (user != null) {
            userRepository.delete(user);
        }
    }

}

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public UserDTO updateUser(UserDTO userDTO) {
        User user = userRepository.findById(userDTO.getId()).orElse(null);
        if (user != null) {
            // 将UserDTO的属性设置到User对象中
            // ...
            userRepository.save(user);
            return userDTO;
        } else {
            return null;
        }
    }

}

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public UserVO getUserById(Long id) {
        User user = userRepository.findById(id).orElse(null);
        if (user != null) {
            return new UserVO(user); // 将User对象转换为UserVO对象，并返回
        } else {
            return null;
        }
    }

}