Spring Boot 3 事件驱动开发全指南：从基础到事务与异常处理

// 普通 Java 对象，无需继承 ApplicationEvent
public class OrderCreatedEvent {
    private final String orderId;
    public OrderCreatedEvent(String orderId) {
        this.orderId = orderId;
    }
    public String getOrderId() { return orderId; }
}

@Service
public class OrderService {
    private final ApplicationEventPublisher publisher;
    public void createOrder(String id) {
        // 业务逻辑...
        publisher.publishEvent(new OrderCreatedEvent(id));
    }
}

@Component
public class OrderEventListener {
    @EventListener
    public void handle(OrderCreatedEvent event) {
        System.out.println("处理订单: " + event.getOrderId());
    }
}

@SpringBootApplication
@EnableAsync // 启用异步
public class App { }
@Component
public class AsyncListener {
    @EventListener
    @Async
    public void handle(OrderCreatedEvent e) {
        // 在独立线程执行，不阻塞主流程
    }
}

@EventListener
public EmailSendEvent handleOrderCreated(OrderCreatedEvent event) {
    return new EmailSendEvent("订单确认邮件"); // 自动 publish！
}
@EventListener
public void handleEmail(EmailSendEvent event) {
    // 处理邮件发送
}

@Transactional
public void createOrder(String id) {
    orderRepo.save(...);
    publisher.publishEvent(new OrderCreatedEvent(id)); // ← 同步监听器在此事务中执行
    if (fail) throw new RuntimeException(); // ← 监听器中的 DB 操作也会回滚！
}

@EventListener
@Async
@Transactional // 开启新事务（与主事务无关）
public void handleAsync(OrderCreatedEvent e) {
    // 独立事务
}

// 加入原事务（默认）
@EventListener
@Transactional
public void handler1(...) { }
// 总是新开事务（即使主事务回滚，此处仍提交）
@EventListener
@Transactional(propagation = Propagation.REQUIRES_NEW)
public void handler2(...) { }

@Component("applicationEventMulticaster")
public class CustomEventMulticaster extends SimpleApplicationEventMulticaster {
    @Override
    public void multicastEvent(ApplicationEvent event) {
        var listeners = getApplicationListeners(event);
        if (listeners.isEmpty()) {
            Object payload = event instanceof PayloadApplicationEvent<?> 
                ? ((PayloadApplicationEvent<?>) event).getPayload()
                : event;
            System.err.println("⚠️ 无人监听的事件: " + payload.getClass());
        }
        super.multicastEvent(event);
    }
}

src/main/java
 └─ com.example.eventdemo
     ├── EventDemoApplication.java
     ├── event/
     │   ├── OrderCreatedEvent.java
     │   └── EmailSendEvent.java
     ├── service/OrderService.java
     └── listener/OrderEventListener.java

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

@Service
@Transactional
public class OrderService {
    private final ApplicationEventPublisher publisher;
    public void createOrder(String id) {
        System.out.println("🛒 创建订单: " + id);
        publisher.publishEvent(new OrderCreatedEvent(id));
    }
}

@Component
public class OrderEventListener {
    @EventListener
    public EmailSendEvent onOrderCreated(OrderCreatedEvent e) {
        System.out.println("✅ 订单事件处理中，当前有事务: " +
            TransactionSynchronizationManager.isActualTransactionActive());
        return new EmailSendEvent("订单 " + e.getOrderId() + " 已确认");
    }
    @EventListener
    public void onEmailSend(EmailSendEvent e) {
        System.out.println("📧 发送邮件: " + e.getMessage());
    }
}