CODEWITHSUNDEEP
javaeventsguava
jeremy303
jeremy303

Reputation: 9251

Guava EventBus: Subscribe without annotations?

I need to implement a pub/sub system within a domain model. I was thinking about using Guava's EventBus, but I'd like to use interfaces and adapters to keep my domain model ignorant of such an implementation detail. Unfortunately, EventBus's use of annotations for subscription throw a monkey wrench at this idea.

Is there any way to subscribe a handler without using the @Subscribe annotation? Looking at the docs, there doesn't seem to be but perhaps there's something I'm not seeing.

Thanks!

Upvotes: 4

Views: 1483

Answers (2)

user2715109
user2715109

Reputation: 351

A workaround is to adapt the Handler. Something like:

class GuavaHandler<T extends Message> implements Handler<T> {
    private Handler<T> handler;

    public GuavaHandler(Handler<T> handler) {
        this.handler = handler;
    }

    @Override
    @Subscribe
    public void handle(T message) {
        try {
            handler.getClass().getMethod("handle", message.getClass());
            handler.handle(message);
        } catch (NoSuchMethodException ignored) {
            // workaround
        }
    }
}

You only define the attribute in this specific implementation.

Upvotes: 1

Louis Wasserman
Louis Wasserman

Reputation: 198591

Guava team member here.

It's quite deliberate that you can only subscribe a handler with the @Subscribe annotation -- EventBus is intended to replace interfaces, adapters, etc., not to supplement them -- but why do you say that exposes more implementation details? In our experience, it usually exposes fewer details.

Upvotes: 7

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