Spring Events

Report an event without directly coupling classes

Sometimes one part of the application needs to say “something happened,” and another part needs to react. You can call the required service directly, but then the sender starts knowing about the receiver. Spring Events lets you loosen that coupling.

record OrderCreated(long orderId) {
}

@Service
class OrderService {
    private final ApplicationEventPublisher publisher;

    OrderService(ApplicationEventPublisher publisher) {
        this.publisher = publisher;
    }

    void create(long orderId) {
        publisher.publishEvent(new OrderCreated(orderId));
    }
}

@Component
class OrderCreatedListener {

    @EventListener
    void on(OrderCreated event) {
        System.out.println("Order: " + event.orderId());
    }
}

OrderService publishes the fact that an order was created, but it does not know who will subscribe to it. The listener declares interest in the event with @EventListener and receives the event object as an argument.

These are in-application events

Spring Events work inside one ApplicationContext. They are not a replacement for Kafka, RabbitMQ, or another message broker. By default, handlers are called synchronously, so publishing the event and running the listener happen in the same execution thread.