Make TransactionalApplicationListenerAdapter support fallbackExecution #34674
Description
I have the following use case.
I have a bean that should act as a multi node event router.
The bean must listen for a particular event interface and broadcast a received event to the other nodes. If a transaction is running, event should be broadcast after commit. If there is no transaction, the event should be immediatly broadcast.
The event interface looks like this:
interface MultiNodeClusterEvent extends Serializable {}The router looks like this:
/**
* @author Réda Housni Alaoui
*/
@Component
class MultiNodeClusterEventRouter {
private final ApplicationEventPublisher eventPublisher;
MultiNodeClusterEventRouter(ApplicationEventPublisher eventPublisher) {
this.eventPublisher = requireNonNull(eventPublisher);
}
@TransactionalEventListener(fallbackExecution = true)
public void onLocalEvent(MultiNodeClusterEvent event) {
// Broadcast to other nodes
}
// Triggered by JGroup
private void onRemoteEvent(MultiNodeClusterEvent event) {
eventPublisher.publishEvent(event);
}
}The obvious issue with this code is that the routers (plural because 1 router/node) may enter in an infinite broadcast loop. The easiest solution that comes to mind is to make the router check the event source and ignore the event if the source is itself. But since I am listening for a raw event, I don't have access to ApplicationEvent informations.
I know that under the cover, Spring use PayloadApplicationEvent for raw events. So I try to implement the infinite loop guard like this:
/**
* @author Réda Housni Alaoui
*/
@Component
class MultiNodeClusterEventRouter extends TransactionalApplicationListenerAdapter<PayloadApplicationEvent<MultiNodeClusterEvent>> {
private final ApplicationEventPublisher eventPublisher;
MultiNodeClusterEventRouter(ApplicationEventPublisher eventPublisher) {
super(event -> {
// Missing fallbackExecution !
// If event.source == this, ignore.
// Else, broadcast to other nodes
});
this.eventPublisher = requireNonNull(eventPublisher);
}
// Triggered by JGroup
private void onRemoteEvent(MultiNodeClusterEvent event) {
eventPublisher.publishEvent(new PayloadApplicationEvent<>(event));
}
}But when I do this, I loose TransactionalApplicationListenerMethodAdapter#fallbackExecution feature.
Could we add this feature to TransactionalApplicationListenerAdapter and pass its activation as an argument to TransactionalApplicationListener#forPayload ?