Including validation into a reactive chain with project reactor - reactive-programming

Question

I would like to compose a reactor chain that would basically do as follows:
Validate a submitted User properties such as the length of the firstName, lastName or validity of the email. I would use the validator below.
Validate that the submitted email is not already used by someone else. I would use a reactive repository for that purpose.
Save the User if all above validation checks pass.
User:
#Builder
#Data
#AllArgsConstructor
#NoArgsConstructor
public class User {
#Id
private Integer id;
private String firstName;
private String lastName;
private String email;
}
Reactive repository:
public interface UserRepository extends ReactiveCrudRepository<User, Long> {
#Query("select id, first_name, last_name, email from user u where u.email = :email")
Mono<User> findByEmail(String email);
}
Validator:
#Component
public class UserValidator implements Validator {
private final static String EMAIL = "email";
private static final String FIRST_NAME = "firstName";
private static final String LAST_NAME = "lastName";
#Override
public boolean supports(Class<?> clazz) {
return User.class.equals(clazz);
}
#Override
public void validate(Object target, Errors errors) {
User user = (User) target;
rejectIfEmptyOrWhitespace(errors, EMAIL, "email.required");
rejectIfEmptyOrWhitespace(errors, FIRST_NAME, "firstName.required");
rejectIfEmptyOrWhitespace(errors, LAST_NAME, "lastName.required");
validateFirstName(errors, user.getFirstName());
validateLastName(errors, user.getLastName());
validateEmail(errors, user.getEmail());
}
private void validateEmail(Errors errors, String email) {
EmailValidator emailValidator = EmailValidator.getInstance();
if (!emailValidator.isValid(email)) {
errors.rejectValue(EMAIL, "email.invalid");
}
}
private void validateFirstName(Errors errors, String firstName) {
if (firstName.length() < 2) {
errors.rejectValue(FIRST_NAME, "firstName.min");
}
}
private void validateLastName(Errors errors, String lastName) {
if (lastName.length() < 2) {
errors.rejectValue(LAST_NAME, "lastName.min");
}
}
}
Handler method:
public Mono<ServerResponse> saveUser(ServerRequest serverRequest) {
return serverRequest.bodyToMono(User.class)
// Use validator here
.flatMap(this::createUserIfEmailNotExists);
}
Helper method:
private Mono<ServerResponse> createUserIfEmailNotExists(User user) {
return userRepository.findByEmail(user.getEmail())
.flatMap(existingUser ->
status(BAD_REQUEST).contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject("User already exists."))
)
.switchIfEmpty(
userRepository.save(user)
.flatMap(newUser -> status(CREATED).contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject(newUser)))
);
}
I am not sure how to go about achieving this from a reactive point of view. Ideally there would be 3 steps in the reactive chain mapping to the points above.
Here is what I have tried but I am having trouble with the method arguments and return types breaking the flow of the sequence...
private Mono<ServerResponse> validateUser(User user) {
Errors errors = new BeanPropertyBindingResult(user, User.class.getName());
userValidator.validate(user, errors);
if (errors.hasErrors()) {
return status(BAD_REQUEST).contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject(errors.getAllErrors()));
} else {
return Mono.empty();
}
}
Can someone please help?

Answer 1

How about this way?
private Mono<ServerResponse> validateUser(User user) {
return Mono.just(new BeanPropertyBindingResult(user, User.class.getName()))
.doOnNext(err -> userValidator.validate(user, err))
.filter(AbstractBindingResult::hasErrors)
.flatMap(err ->
status(BAD_REQUEST)
.contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject(err.getAllErrors()))
);
}
private Mono<ServerResponse> createUserIfEmailNotExists(User user) {
return userRepository.findByEmail(user.getEmail())
.flatMap(existingUser ->
status(BAD_REQUEST).contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject("User already exists."))
)
.switchIfEmpty(
validateUser(user)
.switchIfEmpty(
userRepository.save(user)
.flatMap(newUser -> status(CREATED).contentType(APPLICATION_JSON)
.body(BodyInserters.fromObject(newUser)))
)
);
}