First Release of Java API

This is the master issue to track the progress of formally releasing Java API.

Background

Java worker code was contributed by Ant Financial in 2018 as an experimental feature. It has also been used in the past 2 years internally at Ant. Now we think the code should be stable enough for the formal release.

Action items.

• Simplify usage for beginners: deploy jars (with all platform binaries included) to Maven’s central repo. So that users can use it out of box, without having to compile from code (#6876).
• Make Java version aligned with Python.
• Enhance integration tests for new version releases.
• Finalize API: revisit API design and refine it if needed; avoid making breaking changes after formal release.
• Improve documentation.
• Remove --include-java and --java-worker-options from ray start.

[raulchen]

After some discussions, we decided to upgrade Java API to make it easier to use, more readable, and more consistent with Python.

Remote tasks

Current API

CallOptions options = new CallOptions.Builder.setResources(...).createCallOptions();
RayObject<Integer> res = Ray.call(Foo::foo, 1, options);  // `options` can be omitted.

New API

ObjectRef<Integer> res = Ray.task(Foo::foo, 1).setResource(...).remote(); // `setResource` can be omitted.

Actors

Current API

ActorCreationOptions options = new ActorCreationOpitons.Builder().setResources(...).setMaxRestarts(...).createActorCreationOptions();
RayActor<MyActor> actor = Ray.createActor(MyActor::new, 1, options);
RayObject<Integer> result = actor.call(MyActor::foo, 1);

New API

ActorHandle<MyActor> actor = Ray.actor(MyActor::new, 1)..setResources(...).setMaxRestarts(...).remote();
ObjectRef<Integer> result = actor.task(MyActor::foo, 1).remote();

[kfstorm]

@raulchen Should we update and close this issue?