Java NullReferenceException when using interface

Question

I have a Spring REST API I am developing that keeps returning a NullReferenceException for some reason. I can't figure out why. Here is my code:

The interface:

public interface InitiativesService {
    InitiativeDto createInitiative(InitiativeDto initiativeDto);    
}

The class that implements it:

public class InitiativeServiceImpl implements InitiativesService {

    private final InitiativeRepository initiativeRepository;

    @Autowired
    public InitiativeServiceImpl(InitiativeRepository initiativeRepository)
    {
        this.initiativeRepository = initiativeRepository;
    }

    @Override
    public InitiativeDto createInitiative(InitiativeDto initiativeDto) {
        initiativeRepository.Save(initiativeDto);
    }

The Repository class for communicating to the dB:

@Repository
public interface InitiativeRepository extends JpaRepository<Initiative, Long> {}

And lastly the controller:

public class InitiativesController {

  private InitiativesService initiativesService;
  
  public InitiativesController(InitiativesService initiativesService) {
    this.initiativesService = initiativesService;
  }

  @PostMapping(produces = MediaType.APPLICATION_JSON_VALUE, consumes = MediaType.APPLICATION_JSON_VALUE)
  public ResponseEntity<InitiativeDto> createInitiative(@Valid @RequestBody InitiativeDto initiative) {


    log.info("Saving");
    InitiativeDto createdInitiative = initiativesService.createInitiative(initiative);
    return ResponseEntity.status(HttpStatus.CREATED).body(createdInitiative);
  }

When I try running this and testing via Postman, it returns a NullPointerException. I debug it and I can see the initiativesService is null. I am confused as I have the same implementation for creating Users which works fine without this issue. Can anyone spot any problems I have here?

Which is it? NullReferenceException or NullPointerException? — user207421
– user207421, Commented Mar 2, 2021 at 4:54

Donato Amasa · Accepted Answer · 2021-03-02 03:19:49Z

1

Add @Autowired annotation on your constructor to autowire your initiativeService

@Autowired
public InitiativesController(InitiativesService initiativesService) {
    this.initiativesService = initiativesService;
}

edited Mar 2, 2021 at 3:19

answered Mar 2, 2021 at 3:18

Donato Amasa

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5 Comments

Benjamin M Over a year ago

This should not be needed since Spring 4.x . It automatically autowires the constructor.

Donato Amasa Over a year ago

oh shoot really? I never knew that before. all my life i have been autowiring my services through my constructor using the @Autowired annotation

Yohan Over a year ago

@DonatoAmasa it works now, thank you. I can see its on the other controller but didn't realise it wasn't here. Suspected it would be something small like this.

Benjamin M Over a year ago

@DonatoAmasa Yeah! Here's the Spring 4.3 blog post for this feature: spring.io/blog/2016/03/04/…

Donato Amasa Over a year ago

Sure thing @Yohan! Alright thanks @Benjamin M for the link.

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