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DDD架构实战领域层事件驱动

news 来源：原创 2025/6/7 7:25:02

核心实现：

这种实现方式的优势：

在实际项目中，你可能需要：

事件驱动往往是在一个微服务内部实现的

领域时间是DDD架构中比较常见的概念

在领域层内部的一个模型更改了状态或者发生了一些行为

向外发送一些通知

这些通知叫做领域时间

类似于MQ

这个通知不会在分布式系统内部传递

只会在单个微服务内部传递

和MQ一样这样能解耦

我们可以通过发布事件的方式进行一种松耦合的通信

以下是DDD架构中领域层事件驱动的Java实现示例，展示如何通过领域事件实现松耦合的业务逻辑：

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.function.Consumer;/*** 领域事件接口* 所有领域事件需实现此接口*/
interface DomainEvent {UUID getEventId();LocalDateTime getOccurredOn();
}/*** 领域事件抽象基类* 提供事件ID和发生时间的基础实现*/
abstract class BaseDomainEvent implements DomainEvent {private final UUID eventId;private final LocalDateTime occurredOn;protected BaseDomainEvent() {this.eventId = UUID.randomUUID();this.occurredOn = LocalDateTime.now();}@Overridepublic UUID getEventId() {return eventId;}@Overridepublic LocalDateTime getOccurredOn() {return occurredOn;}
}/*** 订单已创建事件*/
class OrderCreatedEvent extends BaseDomainEvent {private final String orderId;private final String customerId;public OrderCreatedEvent(String orderId, String customerId) {this.orderId = orderId;this.customerId = customerId;}public String getOrderId() {return orderId;}public String getCustomerId() {return customerId;}
}/*** 订单已支付事件*/
class OrderPaidEvent extends BaseDomainEvent {private final String orderId;private final LocalDateTime paymentTime;public OrderPaidEvent(String orderId, LocalDateTime paymentTime) {this.orderId = orderId;this.paymentTime = paymentTime;}public String getOrderId() {return orderId;}public LocalDateTime getPaymentTime() {return paymentTime;}
}/*** 库存扣减事件*/
class InventoryDeductedEvent extends BaseDomainEvent {private final String productId;private final int quantity;public InventoryDeductedEvent(String productId, int quantity) {this.productId = productId;this.quantity = quantity;}public String getProductId() {return productId;}public int getQuantity() {return quantity;}
}/*** 领域事件发布者接口*/
interface DomainEventPublisher {void publish(DomainEvent event);
}/*** 领域事件订阅者接口*/
interface DomainEventSubscriber<T extends DomainEvent> {void handleEvent(T event);Class<T> subscribedToEventType();
}/*** 领域事件总线（单例实现）* 负责事件的注册、发布和分发*/
class DomainEventBus implements DomainEventPublisher {private static final DomainEventBus INSTANCE = new DomainEventBus();private final List<DomainEventSubscriber<?>> subscribers = new ArrayList<>();private DomainEventBus() {}public static DomainEventBus getInstance() {return INSTANCE;}public <T extends DomainEvent> void register(DomainEventSubscriber<T> subscriber) {subscribers.add(subscriber);}@Overridepublic void publish(DomainEvent event) {subscribers.stream().filter(subscriber -> subscriber.subscribedToEventType().isInstance(event)).forEach(subscriber -> dispatch(event, subscriber));}@SuppressWarnings("unchecked")private <T extends DomainEvent> void dispatch(DomainEvent event, DomainEventSubscriber<?> subscriber) {// 同步处理事件((DomainEventSubscriber<T>) subscriber).handleEvent((T) event);// 异步处理示例：// CompletableFuture.runAsync(() -> //     ((DomainEventSubscriber<T>) subscriber).handleEvent((T) event)// );}
}/*** 领域事件聚合根接口* 定义聚合根应具备的事件管理能力*/
interface EventSourcedAggregateRoot {List<DomainEvent> getDomainEvents();void clearDomainEvents();
}/*** 订单实体（聚合根）* 集成领域事件功能*/
class Order implements EventSourcedAggregateRoot {private final String id;private final String customerId;private OrderStatus status;private final List<DomainEvent> domainEvents = new ArrayList<>();public Order(String id, String customerId) {this.id = id;this.customerId = customerId;this.status = OrderStatus.CREATED;// 创建订单时发布订单创建事件registerEvent(new OrderCreatedEvent(id, customerId));}public void pay() {if (status != OrderStatus.CREATED) {throw new IllegalStateException("订单状态错误，当前状态：" + status);}this.status = OrderStatus.PAID;// 支付时发布订单已支付事件registerEvent(new OrderPaidEvent(id, LocalDateTime.now()));}private void registerEvent(DomainEvent event) {domainEvents.add(event);}@Overridepublic List<DomainEvent> getDomainEvents() {return new ArrayList<>(domainEvents);}@Overridepublic void clearDomainEvents() {domainEvents.clear();}// Getterspublic String getId() {return id;}public String getCustomerId() {return customerId;}public OrderStatus getStatus() {return status;}
}/*** 库存服务（领域服务）* 处理库存相关业务逻辑*/
class InventoryService implements DomainEventSubscriber<OrderPaidEvent> {private final InventoryRepository inventoryRepository;public InventoryService(InventoryRepository inventoryRepository) {this.inventoryRepository = inventoryRepository;}@Overridepublic void handleEvent(OrderPaidEvent event) {// 订单支付后扣减库存// 实际应用中需要根据订单ID查询订单详情获取商品信息// 这里简化处理System.out.println("处理订单支付事件：订单ID=" + event.getOrderId());// 扣减库存逻辑// inventoryRepository.deductStock(productId, quantity);// 发布库存扣减事件DomainEventBus.getInstance().publish(new InventoryDeductedEvent("P001", 1));}@Overridepublic Class<OrderPaidEvent> subscribedToEventType() {return OrderPaidEvent.class;}
}/*** 库存仓储接口*/
interface InventoryRepository {void deductStock(String productId, int quantity);
}/*** 库存仓储实现（示例）*/
class InMemoryInventoryRepository implements InventoryRepository {@Overridepublic void deductStock(String productId, int quantity) {System.out.println("扣减库存：商品ID=" + productId + "，数量=" + quantity);// 实际实现会更新数据库中的库存记录}
}/*** 订单服务（应用服务）* 协调领域对象和事件处理*/
class OrderApplicationService {private final OrderRepository orderRepository;private final DomainEventPublisher eventPublisher;public OrderApplicationService(OrderRepository orderRepository, DomainEventPublisher eventPublisher) {this.orderRepository = orderRepository;this.eventPublisher = eventPublisher;}public void createOrder(String customerId, List<OrderItem> items) {// 创建订单String orderId = UUID.randomUUID().toString();Order order = new Order(orderId, customerId);// 持久化订单orderRepository.save(order);// 发布领域事件publishEvents(order);}public void payOrder(String orderId) {// 获取订单Order order = orderRepository.findById(orderId).orElseThrow(() -> new IllegalArgumentException("订单不存在"));// 执行支付业务逻辑order.pay();// 持久化更新orderRepository.save(order);// 发布领域事件publishEvents(order);}private void publishEvents(Order order) {order.getDomainEvents().forEach(eventPublisher::publish);order.clearDomainEvents();}
}/*** 订单仓储接口*/
interface OrderRepository {void save(Order order);java.util.Optional<Order> findById(String orderId);
}/*** 主程序演示*/
public class Main {public static void main(String[] args) {// 初始化组件InventoryRepository inventoryRepository = new InMemoryInventoryRepository();InventoryService inventoryService = new InventoryService(inventoryRepository);OrderRepository orderRepository = new InMemoryOrderRepository();DomainEventPublisher eventPublisher = DomainEventBus.getInstance();// 注册事件订阅者DomainEventBus.getInstance().register(inventoryService);// 初始化订单应用服务OrderApplicationService orderService = new OrderApplicationService(orderRepository, eventPublisher);// 创建订单orderService.createOrder("C001", Collections.emptyList());// 支付订单（触发事件）orderService.payOrder("ORD12345");}
}

这个示例展示了DDD领域层事件驱动的