Cleaning some codes

[sardorbek-matniyazov]

in Chapter #6
You can also use functional programming in this class EmailVerificationService.
but I might change some code of EmailVerificationRepository like this .
EmailVerificationService interface

`public interface EmailVerificationService {

String generateVerification(String username);

String getVerificationByUsername(String username);

String getUsernameForVerificationId(String verificationId);

}`

and
EmailVerificationServiceImpl class

`@Service
public class EmailVerificationServiceImpl implements EmailVerificationService {
private final EmailVerificationRepository repository;

@Autowired
public EmailVerificationServiceImpl(EmailVerificationRepository repository) {
    this.repository = repository;
}

@Override
public String generateVerification(String username) {
    Optional<EmailVerification> byUsername = repository.findByUsername(username);
    return byUsername.orElse(
            repository.save(
                    EmailVerification.builder()
                            .username(username)
                            .build()
            )
    ).getUsername();
}

@Override
public String getVerificationByUsername(String username) {
    return repository.findByUsername(username).map(EmailVerification::getUsername).orElse(null);
}

@Override
public String getUsernameForVerificationId(String verificationId) {
    return repository.findById(verificationId).map(EmailVerification::getVerificationId).orElse(null);
}

}`

EmailVerificationRepository interface

public interface EmailVerificationRepository extends JpaRepository<EmailVerification, String> { Optional<EmailVerification> findByUsername(String username); }

but I'm using @builder in Entity classes
this is how I used functional programming in this project

[krnsehgal06-gif]

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