Validating user inputs on service methods in a cleaner way

Question

In a project, we use service methods, there, we have to validate certain required inputs for our business logic to work:

public void exampleMethod(final UserDto user, String sthElse) {
  if (user.getId() == null) {
    throw new CustomHandledException("example");
  }
  if (sthElse == null) {
    throw new CustomHandledException("example");
  }

  GetUserResponseDto getUserResponse = client.getUserById(user.getId(), country);

  if (getUserResponse == null) {
    if (user.getGivenName() == null) {
      throw new CustomHandledException("example");
    }
    if (user.getEmail() == null) {
      throw new CustomHandledException("example");
    }
    CreateUserRequestDto createUserBody = UserMapper.toCreateBody(user);
    client.createUser(createUserBody);
    return;
  }

  if (user.getLocale().equals(getUserResponse.getUser().getProfile().getLocale())){
      return;
  }

  client.updateUser(user);
}

Even though the code isn't necessarily wrong and is quite understandable (for me) I feel like there is something odd there, do you have any suggestions for a cleaner code?

I tried to write clean code, however, it doesn't feel like it is clean.

Answer 1

We could go by AOP solutions or by extracting validations to a method as below

public void exampleMethod(final UserDto user, String sthElse) {
        validateUser(user);

        if (sthElse == null) {
            throw new CustomHandledException("example");
        }

        GetUserResponseDto getUserResponse = client.getUserById(user.getId(), country);

        if (getUserResponse == null) {
            CreateUserRequestDto createUserBody = UserMapper.toCreateBody(user);
            client.createUser(createUserBody);
            return;
        }

        if (user.getLocale().equals(getUserResponse.getUser().getProfile().getLocale())){
            return;
        }
        // validations needs to be done before updating as well by convention
        // since validations were done while inserting
        client.updateUser(user);
    }

    private boolean validateUser(UserDto userDto) {

        //these declarations could be moved at class fields or constant
        Predicate<UserDto> customDtoCheck = user ->user.getGivenName().startsWith("text");
        Predicate<String> emailValidation = RequestValidator::validateEmail;
        Predicate notNull = RequestValidator::notNull;

        boolean validUser = notNull.test(userDto) &&
                            notNull.test(userDto.getId()) &&
                            notNull.test(userDto.getGivenName()) &&
                            notNull.test(userDto.getEmail()) &&
                            notNull.test(userDto.getLocale()) &&
                            emailValidation.test(userDto.getEmail()) &&
                            customDtoCheck.test(userDto);
        if (!validUser)
            throw new CustomHandledException("example");

        return validUser;
    }