Axon & CompletableFuture

问题

I've faced with problems when i try to use CompletableFuture with Axon. For example:

CompletableFuture future = CompletableFuture.supplyAsync(() -> {

            log.info("Start processing target: {}", target.toString());
            return new Event();

        }, threadPool);

future.thenAcceptAsync(event -> {
            log.info("Send Event");
            AggregateLifecycle.apply(event);
}, currentExecutor);

in thenAcceptAsync - AggregateLifecycle.apply(event) has unexpected behavior. Some of my @EventSourcingHandler handlers start handling event twice. Does anybody know how to fix it?

I have been reading docs and everything that i got is:

In most cases, the DefaultUnitOfWork will provide you with the functionality you need. It expects processing to happen within a single thread.

so, it seems i should use somehow CurrentUnitOfWork.get/set methods but still can't understand Axon API.

回答1:

You should not apply() events asynchronously. The apply() method will call the aggregate's internal @EventSourcingHandler methods and schedule the event for publication when the unit of work completes (successfully). The way Axon works with the Unit of Work (which coordinates activity of a single message handler invocation), the apply() method must be invoked in the thread that manages that Unit of Work.

If you want asynchronous publication of Events, use an Event Bus that uses an Async Transport, and use Tracking Processors.

来源：https://stackoverflow.com/questions/52937596/axon-completablefuture