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Current state: Under Discussion [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: here

JIRA: here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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The default implementation of new API is based on existent method so binary compatibility is safe. Also, in order to simplify the users' migration, the existent serialize methods are marked as deprecated and all of they get default implementation, which throw UnsupportedOperationException. Hence, users who don’t want to extend deprecated methods can migrate to new API safely. Of course, we should not call deprecated serialize methods anymore so the user-defined serializer which extends only new interface is able to work.

Apart from Serializer, Partitioner also need some updates since it still accept byte[]. The purposed changes are similar to Serializer that we replace byte[] by ByteBuffer. Also, the new API get default implementation based on existent method.

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org.apache.kafka.common.serialization.Serializer

    @Deprecated
    default byte[] serialize(String topic, T data) {
        throw new UnsupportedOperationException("this method is not used on production anymore");
    }

    @Deprecated
    default byte[] serialize(String topic, Headers headers, T data) {
        return serialize(topic, data);
    }

    default ByteBuffer serialize(String topic, T data, Headers headers) {
        byte[] array = serialize(topic, headers, data);
        return array == null ? null : ByteBuffer.wrap(array);
    }

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org.apache.kafka.clients.producer.Partitioner

    @Deprecated
    default int partition(String topic, Object key, byte[] keyBytes, Object value, byte[] valueBytes, Cluster cluster) {
        throw new UnsupportedOperationException("this method is not used on production anymore");
    }

    default int partition(String topic, Object key, ByteBuffer keyBytes, Object value, ByteBuffer valueBytes, Cluster cluster) {
        return partition(topic, key, Utils.getOrCopyArray(keyBytes), value, Utils.getOrCopyArray(valueBytes), cluster);
    }

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