如何将服务注入监听器？

Question

我的目标是通过 AuditTrailListener 监听用户实体 并在插入/更新/删除操作时将审计数据保存到数据库中 在用户上执行。发生某些操作后，我可以收听并打印消息。问题是当我想将 AuditService 的实例注入 AuditTrailListener 并将 AuditObject 数据存储到数据库时。我得到 NullPointerException。关于如何解决问题的选项很少（例如静态字段），但它们都不起作用？

用户.java

@Entity
@EntityListeners(AuditTrailListener.class)
public class User {
    private static Log log = LogFactory.getLog(User.class);

    @Id
    @GeneratedValue
    private int id;
    
    private String userName;
}

AuditObject.java

@Getter
@Setter
@Entity(name="AuditObject")
public class AuditObject {
    @Id
    @GeneratedValue
    private int id=1L;  // test
    
    @Column(length=20)
    private String op="test1"; // test
}

AuditRepository.java

@Repository
public interface AuditRepository extends JpaRepository<AuditObject, Long> {
    List<AuditObject> findAll();
}

AuditService.java

@Service
@RequiredArgsConstructor    // lombok
@Transactional
public class AuditService {
    private final AuditRepository repo;

    public Audit saveOrUpdate(Audit audit) {
        return repo.save(audit);
    }
}

AuditTrailListener.java

public class AuditTrailListener {

    static private AuditService auditService;

    @Autowired
    public void init(AuditService auditService)
    {
        AuditTrailListener.auditService = auditService;
    }

    @PrePersist
    @PreUpdate
    @PreRemove
    private void beforeAnyUpdate(User user) {
        System.out.println(user);
        auditService.saveOrUpdate(new AuditObject());//java.lang.NullPointerException
    }
    
    @PostPersist
    @PostUpdate
    @PostRemove
    private void afterAnyUpdate(User user) {
        System.out.println(user);
        auditService.saveOrUpdate(new AuditObject());//java.lang.NullPointerException
    }
    
    @PostLoad
    private void afterLoad(User user) {
        System.out.println(user);
        auditService.saveOrUpdate(new AuditObject());//java.lang.NullPointerException
    }
}

Answer 1

您需要将 AuditTrailListener 设为 Spring 管理的 Bean。一种简单的方法是使用@Component 对其进行注释，如下所示：

@Component
public class AuditTrailListener {
   (...)
}