Status

Current state: "Under Discussion", "Accepted", "Rejected"

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JIRA:

Motivation

KafkaFuture.Function and KafkaFuture.BiCosumer are currently empty public abstract classes with one abstract method.

This means you cannot implement them with a java 8 lambda, as that only works for functional interfaces.

Public Interfaces

From the public interfcate, only org.apache.kafka.common.KafkaFuture has such helper classes.

Proposed Changes

The current proposal implemented in PR#4033 makes from those abstract classes interfaces.

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This will eventually become a thin shim on top of Java 8's CompletableFuture.

Compatibility, Deprecation, and Migration Plan

When the change is implemented like proposed, everybody using this api will need to implement instead of extend their implementations of KafkaFuture.Function and KafkaFuture.Biconsumer.

Other Alternatives

• Keep the current interface as is, as a nicer syntax to address this api might not be worth breaking backwards compatibility
• Wait for a kafka release which will not support java 7 anymore.  A backwards incompatible change can then be done to replace KafkaFuture with CompletableFuture
• Spend more effort and update the definition of KafkaFuture in such a way that it gradually switches to CompletableFuture.  By following an approach which looks like this:
  • Create new interface versions of KafkaFuture.Function and KafkaFuture.BiConsumer, create new methods which handle those functional interface and preferably line their names up with those of CompletableFuture.  So for example KafkaFuture.addWaiter(BiConsumer) becomes KafkaFuture.whenComplete(BiConsumerInterface).  Mark the old methods as @Deprecated.
  • When kafka does not support java 7 anymore, let KafkaFuture extend CompletableFuture (or even CompletionStage)
  • Later on the deprecated methods can be removed, and KafkaFuture becomes a shim on Completablefuture or CompletionStage.