[도메인 주도 개발 시작하기] - 이벤트

public class Order { ... // 외부 서비스를 실행하기 위해 도메인 서비스를 파라미터로 전달받음 public void cancel(RefundService refunService) { verifyNotYetShipped(); this.state = OrderState.CANCELD; this.refundStatus = State.REFUND_STRTED; try { reFundService.refund(getPaymentId()); this.refundStatus = State.REFUND_COMPLTED; } catch (Exception ex) { ??? } } }

public class CancelOrderService { private RefundService refundService; @Transcation public void cancel(OrderNo orderNo) { Order order = findOrder(orderNo); order.cancel(); order.refundStarted(); try { refundService.refund(order.getPaymentId); // 외부 서비스 성능에 직접 영향을 받는다. order.refundCompleted(); } catch { ??? } } }

public class Order { // 기능을 추가할 때마다 파라미터가 함께 추가되면 // 다른 로직이 더 많이 섞이고, 트랜잭션 처리가 더 복잡해진다. public void cancel(RefundService refunService, NotiService notiSvc) { verifyNotYetShipped(); this.state = OrderState.CANCELD; ... // 주문 + 결제 + 통지 로직이 섞임 // reufndService는 성공하고, notiSvc는 실패하면? // refundService와 notiSvc 중 무엇을 먼저 처리하냐? } }

public class ShippingInfoChangedEvent { private String orderNumber; private long timestamp; private ShippingInfo newShippingInfo; // 생성자, getter }

public class Order { ... public void changeShippingInfo(ShippingInfo newShippingInfo) { verifyNotYetShipped(); setShippingInfo(newShippingInfo); Events.raise(new ShippingInfoChangedEvent(number, newShippingInfo)); } ... }

public class ShippingInfoChangedHandler { @EventsListener(ShippingInfoChangedEvent.class) public void handle(ShippingInfoChangedEvent evt) { // 이벤트가 필요한 데이터를 담고 있지 않으면, // 이벤트 핸들러는 리포지터리, 조회 API, 직접 DB 접근 등의 // 방식을 통해필요한 데이터를 조회해야 한다. shippingInfoSyncronizer.sync( evt.getOrderNumber(), evt.getShippingInfo()); } ... }

public class CancelOrderService { private RefundService refundService; @Transcation public void cancel(OrderNo orderNo) { Order order = findOrder(orderNo); order.cancel(); order.refundStarted(); try { refundService.refund(order.getPaymentId); // 외부 서비스 성능에 직접 영향을 받는다. order.refundCompleted(); } catch { ??? } } }

public class Order { ... public void cancel() { verifyNotYetShipped(); this.state = OrderState.CANCELED; Events.raise(new OrderCanceledEvent(number.getNumber())); } ... }

public class OrderCanceledEvents { // 이벤츠는 핸들러에서 이벤트를 처리하는데 필요한 데이터를 포함한다. private String orderNumber; public OrderCanceledEvent(String number) { this.orderNumber = number; } public String getOrderNumber() {return orderNumber;} }

public abstract class Event { private long timestamp; public event() { this.timestamp = System.currentTimeMillis(); } public long getTimestamp() { return this.timestamp; } }

public class Events { private static ApplicationEventsPublisher publisher; static void setPulisher(ApplicationEventsPublisher publisher) { Events.publisher = publisher; } public static void raise(Object event) { if (publisher != null) { publisher.publisherEvent(event); } } }

@Configureation public class EvnetsConfiguration { @Autwired private ApllicationContext applicationContext; @Bean public InitializingBean eventsInitializer() { return () -> Events.setPublisher(applicationContext); } }

public class Order { public void cancel() { verifyNotYetShipped(); this.state = OrderState.CANCLED; Events.raise(new OrderCanceledEvents(nuber.getNumber())); } }

@Service public class OrderCanceledEventHandler { private RefundSevice refundSevice; public OrderCancledEventHandler(RefundSevice refundSevice) { this.refundSevice = refundSevice; } @EventListener(OrderCanceledEvent.class) public void handle(OrderCanceledEvent event) { refundSevice.fund(event.getOrderNumber()); } }

// 1. 응용 서비스 코드 @Trnasactional // 외부 연동 과정에서 익셉션이 발생하면 트랜잭션 처리는? public void cancel(OrderNo orderNo) { Order order = findOrder(orderNo); order.cancle(); // order.cancel()에서 OrderCanceledEvent 발생 } // 2. 이벤트를 처리하는 코드 @Service public class OrderCanceledEventHandler { ... @EventListener(OrderCanceledEvent.class) public void handle(OrderCanceledEvent event) { // refundService.refund()가 느려지거나 익셉션이 발생한다면? refundService.refund(event.getOrderNumber()); } }

@SpringBootApplication @EnableAsync public class ShopApplication { public static void main(String [] args) { SpringApplication.run(ShopApplication.class, args); } }

@Service public class OrderCancelEventHandler { @Async @EventListner(OrderCanceledEvent.class) public void handle(OrderCanceledEvent event) { refundService.refund(event.getOrderNumber()); } }

public class EventEntry { private Long id; private String type; private String contentType; private String payload; private long timestamp; public EventEntry(String type, String contentType, String payload) { this.type = type; this.contentType = contentType; this.payload = payload; this.timestamp = System.currentTimeMillis(); } public EventEntry(Long id, String type, String contentType, String payload, long timestamp) { this.id = id; this.type = type; this.contentType = contentType; this.payload = payload; this.timestamp = timestamp; } public Long getId() { return id; } public String getType() { return type; } public String getContentType() { return contentType; } public String getPayload() { return payload; } public long getTimestamp() { return timestamp; } }

public interface EventStore { void save(Object event); List<EventEntry> get(long offset, long limit); }

@Component public class JdbcEventStore implements EventStore { private ObjectMapper objectMapper; private JdbcTemplate jdbcTemplate; public JdbcEventStore(ObjectMapper objectMapper, JdbcTemplate jdbcTemplate) { this.objectMapper = objectMapper; this.jdbcTemplate = jdbcTemplate; } @Override public void save(Object event) { EventEntry entry = new EventEntry(event.getClass().getName(), "application/json", toJson(event)); jdbcTemplate.update( "insert into evententry " + "(type, content_type, payload, timestamp) " + "values (?, ?, ?, ?)", ps -> { ps.setString(1, entry.getType()); ps.setString(2, entry.getContentType()); ps.setString(3, entry.getPayload()); ps.setTimestamp(4, new Timestamp(entry.getTimestamp())); }); } private String toJson(Object event) { try { return objectMapper.writeValueAsString(event); } catch (JsonProcessingException e) { throw new PayloadConvertException(e); } } @Override public List<EventEntry> get(long offset, long limit) { return jdbcTemplate.query( "select * from evententry order by id asc limit ?, ?", ps -> { ps.setLong(1, offset); ps.setLong(2, limit); }, (rs, rowNum) -> { return new EventEntry( rs.getLong("id"), rs.getString("type"), rs.getString("content_type"), rs.getString("payload"), rs.getTimestamp("timestamp").getTime()); }); } }

create table evententry ( id int not null AUTO_INCREMENT PRIMARY KEY, `type` varchar(255), `content_type` varchar(255), payload MEDIUMTEXT, `timestamp` datetime ) character set utf8mb4;

@Component public class EventStoreHandler { private EventStore eventStore; public EventStoreHandler(EventStore eventStore) { this.eventStore = eventStore; } @EventListener(Event.class) public void handle(Event event) { eventStore.save(event); } }

@RestController public class EventApi { private EventStore eventStore; public EventApi(EventStore eventStore) { this.eventStore = eventStore; } @RequestMapping(value = "/api/events", method = RequestMethod.GET) public List<EventEntry> list( @RequestParam("offset") Long offset, @RequestParam("limit") Long limit) { return eventStore.get(offset, limit); } }

@Component public class EventForwarder { private static final int DEFAULT_LIMIT_SIZE = 100; private EventStore eventStore; private OffsetStore offsetStore; private EventSender eventSender; private int limitSize = DEFAULT_LIMIT_SIZE; public EventForwarder(EventStore eventStore, OffsetStore offsetStore, EventSender eventSender) { this.eventStore = eventStore; this.offsetStore = offsetStore; this.eventSender = eventSender; } @Scheduled(initialDelay = 1000L, fixedDelay = 1000L) public void getAndSend() { long nextOffset = getNextOffset(); List<EventEntry> events = eventStore.get(nextOffset, limitSize); if (!events.isEmpty()) { int processedCount = sendEvent(events); if (processedCount > 0) { saveNextOffset(nextOffset + processedCount); } } } private long getNextOffset() { return offsetStore.get(); } private int sendEvent(List<EventEntry> events) { int processedCount = 0; try { for (EventEntry entry : events) { eventSender.send(entry); processedCount++; } } catch(Exception ex) { // 로깅 처리 } return processedCount; } private void saveNextOffset(long nextOffset) { offsetStore.update(nextOffset); } }

public interface OffsetStore { long get(); void update(long nextOffset); }

public interface EventSender { void send(EventEntry event); }

@TransactionalEventListener( classes = OrderCancledEvent.class, phase = TransactionPhase.AFTER_COMMIT ) public void handle(OrderCanceledEvent event) { refundService.refund(event.getIrderNumber()); }