Java 使用接口时出现 NullReferenceException

Question

我有一个 Spring REST API 我正在开发它由于某种原因不断返回 NullReferenceException。我不知道为什么。这是我的代码：

接口：

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

实现它的class：

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);
    }

用于与 dB 通信的存储库 class：

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

最后是控制器：

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);
  }

当我尝试运行并通过 Postman 进行测试时，它 returns 出现 NullPointerException。我调试它，我可以看到 initiativesService 为空。我很困惑，因为我有相同的创建用户的实现，它在没有这个问题的情况下工作正常。谁能发现我在这里遇到的任何问题？

Answer 1

在您的构造函数上添加 @Autowired 注释以自动装配您的 initiativeService

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

Java 使用接口时出现 NullReferenceException

Java NullReferenceException when using interface

java

spring

interface

nullpointerexception