Spring custom validation annotation isn't working because of null pointer exception?

Question

I have this custom annotation interface:

@Documented
@Constraint(validatedBy = NameValidator.class)
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD})
public @interface NameValidation {

    String message() default "Name invalid";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

which has this NameValidator class:

public class NameValidator implements ConstraintValidator<NameValidation, String> {

    @Autowired
    private NicknameRepository nicknameRepository;

    @Override
    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        return nicknameRepository.existsById(1L);
    }
}

NameValidator needs an autowired repository object to test a value in the Database.

Nickname repository

@Repository
public interface NicknameRepository extends JpaRepository<Nickname, Long> {

}

The Enitity and use of custom annotation:

@Entity
@Getter
@Setter
@NoArgsConstructor
@Table(name = "Nickname")
@ToString
public class Nickname extends RepresentationModel<Nickname> {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false)
    private Long id;

    @Column(name = "nicknameValue")
    private String nicknameValue;

    @Column(name = "byUser")
    @NameValidation(message = "Name is invalid")   // using custom annotation
    private String byUser;

}

When I run the application and try to add a new Nickname I get an error. The nickname repository in the NameValidator class is null.

This is the error I get.

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed: jakarta.validation.ValidationException: HV000028: Unexpected exception during isValid call.] with root cause

java.lang.NullPointerException: Cannot invoke "com.proj.repository.NicknameRepository.existsById(Object)" because "this.nicknameRepository" is null

I have tried many different answers on stackoverflow already such as adding @Service/@Component to NameValidator etc but for some reason Spring still isn't autowiring the nickname repository. Autowiring the nickname repository in other classes seems to work fine.

Answer 1

Did you try to add this configuration bean?

@Configuration
public class ValidationConfig {
    @Bean
    public Validator validator () {
      return new LocalValidatorFactoryBean();
    }

    @Bean
    public MethodValidationPostProcessor     methodValidationPostProcessor() {
      MethodValidationPostProcessor  methodValidationPostProcessor = new      MethodValidationPostProcessor();
      methodValidationPostProcessor.setValidator(validator());

      return methodValidationPostProcessor;
    }
}