Event Driven Architecture

事件驅動設計

行為松耦合制度，提升未來擴充性

姓名變更簡單範例

定義事件

1. 已提交姓名變更事件

2. 已驗證失敗事件

3. 已變更姓名事件

graph LR;
    cmd(提交commmand) --> submit
    submit(已提交Event)-->ok(已完成姓名變更Event);
    submit-->fail(已驗證失敗Event);
  

事件監聽

當【事件發生】，驅動另一件事件

@Slf4j
@RequiredArgsConstructor
public class NamedEventChannel implements IChannel<NamedEvent> {

	private final ChangeNameUseCase changeNameUseCase;

	@Override
	public void dispatch(NamedEvent message) {
		changeNameUseCase.change(message);
	}

}

題目

1. 身分證、變更後姓名必填

2. 變更後姓名不得空白

3. 姓名變更最多3次

定義聚合根

使用者【UserAggregate】

/**
 * 使用者
 *
 */
@Data
public class UserAggregate {

	private String id;// 統一編號
	private String name;
	private int changeNameCount = 0;// 姓名變更次數

測試Happy Path路徑

	/**
	 * 輸入正確性名，變更次數小於等於3，取得變更成功事件
	 */
	@Test
	void testCurrentNameAndCountLess3ReturnNamedEvent() {

		// GIVE
		SubmitNameUseCommand submitNameUseCommand = new SubmitNameUseCommand();
		submitNameUseCommand.setId(A123456789);
		submitNameUseCommand.setNewNmae(NEW_NAME);

		// WHEN
		UserAggregate userAggregate = new UserAggregate();
		userAggregate.setId(A123456789);
		userAggregate.setName(A123456789);
		userAggregate.setName(OLD_NAME);
		userAggregate.setChangeNameCount(0);

		Mockito.when(userAggregateRepository.findById(A123456789)).thenReturn(userAggregate);

		// THEN
		SubmitNameUseCase submitNameUseCase = new SubmitNameUseCase(userAggregateRepository);
		Event event = submitNameUseCase.submit(submitNameUseCommand);
		assertThat(event).isExactlyInstanceOf(NamedEvent.class);

		NamedEvent namedEvent = (NamedEvent) event;
		assertThat(namedEvent.getId()).isEqualTo(A123456789);
		assertThat(namedEvent.getNewName()).isEqualTo(NEW_NAME);
		assertThat(namedEvent.getOldName()).isEqualTo(OLD_NAME);
		assertThat(namedEvent.getChangeNameCount()).isEqualTo(1);

	}

撰寫提交案例

@RequiredArgsConstructor
public class SubmitNameUseCase {

	private final IUserAggregateRepository userAggregateRepository;

	Event submit(SubmitNameUseCommand command) {
		UserAggregate user = userAggregateRepository.findById(command.getId());
		if (user == null) {
			VerifiedFailNameEvent verifiedFailNameEvent = new VerifiedFailNameEvent();
			verifiedFailNameEvent.setMessage("帳號不存在:" + command.getId());
			return verifiedFailNameEvent;
		}
		return user.changeName(command);
	}

}

使用者行為操作

@Data
public class UserAggregate {

	private String id;// 統一編號
	private String name;
	private int changeNameCount = 0;// 姓名變更次數

	public Event changeName(SubmitNameUseCommand command) {
		try {
			this.checkchangeName(command);

			final NamedEvent namedEvent = new NamedEvent();
			namedEvent.setOldName(this.name);
			namedEvent.setNewName(command.getNewNmae());
			namedEvent.setId(id);
			namedEvent.setChangeNameCount(++changeNameCount);
			this.name = command.getNewNmae();
			return namedEvent;
		} catch (ApBusinessException e) {
			VerifiedFailNameEvent verifiedFailNameEvent = new VerifiedFailNameEvent();
			verifiedFailNameEvent.setMessage(e.getMessage());
			return verifiedFailNameEvent;
		}

	}