Spring Boot multiple sync & async application event listeners

Question

I have 3 event listeners listening on the same event:

1. Save in DB
2. Cache
3. Publish message

Where 1 and 2 execute synchronously in order and 3 independently and asynchronously. I have enabled @EnableAsync.

    @Order(1)
    @EventListener
    fun handle(update: String) {
        logger.info("Database $update")
        //throw IOException()
    }

    @Order(2)
    @EventListener
    fun handle(update: String) {
        logger.info("Cache $update")
    }

    @Async
    @EventListener
    fun handle(update: String) {
        logger.info("Kafka $update")
    }

Works as expected:

[nio-8080-exec-4] controller.Listener2               : Database user22
[nio-8080-exec-4] controller.Listener1               : Cache user22
[        task-21] controller.Listener3               : Kafka user22

Problem arises when Database handler fails:

[nio-8080-exec-7] controller.Listener2               : Database user22
[nio-8080-exec-7] controller.Controller              : Failed to invoke event listener

Why wouldn't the asynchronous event listener get executed?

Answer 1

You can think about it as if the event dispatcher does not know anything about the @Async annotation. So the dispatcher calls the three methods in your designated order (or, as here, if you didn’t add an order, then in the default order) synchronously.

Only then, upon calling the proxied async method, the async proxy starts the original method in another thread.

The async proxy and the event dispatcher operate independently and don’t know about each other.