Make ListenableFuture lambda compliant [SPR-11820]

[spring-projects-issues]

Sébastien Deleuze opened SPR-11820 and commented

When building a Spring 4 / Java 8 application, we can't use lambda with ListenableFuture since ListenableFutureCallback is not a functional interface (2 methods to implement).

5 proposals to improve this:

1. Modify ListenableFutureCallback: it will break API so it is not an option (even if it would be the cleaner solution)
2. Add another method to ListenableFuture with a callback parameter with just one method like mongoDB MongoFuture and SingleResultCallback.
3. Add new fluent methods to ListenableFuture with single method callbacks allowing to write code like listenableFuture.onSuccess(...).onFailure(...)
4. Add default implementation to ListenableFutureCallback#onFailure() interface : not possible since it would require Java 8 for main code
5. Change nothing and wait for a future version of Spring that will require Java 8 and use native CompletableFuture

My prefered solution is the 3rd.

Any feedback or advice ?

---

Affects: 4.0.5

Issue Links:

• Create a synchronous SettableListenableFuture implementation [SPR-11614] #16237 Create a synchronous SettableListenableFuture implementation
• Make ListenableFuture chainable [SPR-12867] #17465 Make ListenableFuture chainable

Referenced from: commits 4e25a14, 86e8bda

1 votes, 5 watchers

[spring-projects-issues]

Juergen Hoeller commented

As discussed yesterday, I'm in favor of option 3 as well. Let's try to roll this into 4.1 still.

Juergen

[spring-projects-issues]

Sébastien Deleuze commented

Here is my first try, feedbacks welcomed !

[spring-projects-issues]

Rossen Stoyanchev commented

The name ListenableFutureBuilder doesn't seem right. More importantly though the current proposal allows adding one success and one failure callback only. Then the builder returns ListenableFutureCallback which is odd since a callback should be input, not a return value. I'd expect to be able to chain onSuccess and onFailure callbacks in any order.

Shouldn't it look something like this:

public interface ListenableFuture<T> extends Future<T> {

	void addCallback(ListenableFutureCallback<? super T> callback);

	ListenableFuture<T> onSuccess(ListenableFutureSuccessCallback<T> callback);

	ListenableFuture<T> onFailure(ListenableFutureFailureCallback callback);

}

[spring-projects-issues]

Sébastien Deleuze commented

Thanks for your feedback Rossen Stoyanchev. Here is a second try that match with your API proposal.

[spring-projects-issues]

Sébastien Deleuze commented

Pull request #571 submitted.