[20210220] (Spring) BeanUtils.copyProperties(), Event Handling(Pub-Sub)

[JuHyun419]

BeanUtils.copyProperties()

• 정리

Guava의 EventBus ... Event Driven(Comment<댓글> Event)

// Service Layer 
private final EventBus eventBus;

eventBus.post(new CommentCreatedEvent(comment));


// CommentCreatedEvent는 댓글 관련 Entity
public class CommentCreatedEvent {

  private final Id<Post, Long> postId;
  private final Id<User, Long> userId;
  private final Writer commentWriter;
  private final Id<Comment, Long> commentId;
  ...


// CommentCreatedEventListener
public class CommentCreateEventListener implements AutoCloseable {

  private final EventBus eventBus;

  private final PostService postService;

  private final KafkaTemplate<String, CommentCreatedMessage> kafkaTemplate;

  public CommentCreateEventListener(EventBus eventBus,
                                    PostService postService,
                                    KafkaTemplate<String, CommentCreatedMessage> kafkaTemplate) {
    this.eventBus = eventBus;
    this.postService = postService;
    this.kafkaTemplate = kafkaTemplate;
    eventBus.register(this);  // 등록.. 이벤트를 구독할 수 있는 상태
  }

  /**
   * EventBus를 등록하고 EventBus에 특정 Event를 발송하면
   * EventBus가 그 Event를 SubScribe하고 있는 대상에게 알아서 전달해주는 역할
   * 컨트롤러나 서비스가 CommentCreateEventListener에 대한 존재를 알 필요가 없이, EventBus만 바라보고 있으면 된다.
   * Service의 eventBus.post(new CommentCreateEvent(comment));를 통해 아래 메서드가 호출됨
   */
  @Subscribe
  public void handleCommentCreateEvent(CommentCreatedEvent event) throws Exception {
    Id<Post, Long> postId = event.getPostId();

    // Kafka 에게 발송(send) 로직
    ....
  }


  // Event Configure 설정
  @Bean
  public EventBus eventBus(TaskExecutor eventTaskExecutor, EventExceptionHandler eventExceptionHandler) {
    return new AsyncEventBus(eventTaskExecutor, eventExceptionHandler);
  }

  @Bean()
  public CommentCreateEventListener commentCreateEventListener(EventBus eventBus, PostService postService, KafkaTemplate kafkaTemplate) {
    return new CommentCreateEventListener(eventBus, postService, kafkaTemplate);
  }

References

https://www.baeldung.com/guava-eventbus