@Override
    public void returnSharedKafkaProducer(final SharedKafkaProducer sharedKafkaProducer) {

        if (sharedKafkaProducer != null && sharedKafkaProducer.hasKafkaProducer()) {
            sharedKafkaProducer.close();
        }
    }
Class to provide shared {@link KafkaProducer} instances wrapped inside a {@link SharedKafkaProducer}.
We want one {@link KafkaProducer} per {@link KafkaConfigDoc}, however the config in a {@link KafkaConfigDoc}
can change at runtime so on each request for a {@link SharedKafkaProducer} we need to check if the
{@link KafkaConfigDoc} has changed since the time we created it. New calls to
{@link KafkaProducerFactory#getSharedProducer(DocRef)} will always get a {@link SharedKafkaProducer} for the
latest config. {@link KafkaProducer}
stroom-kafka/stroom-kafka-impl/src/main/java/stroom/kafka/impl/KafkaProducerFactoryImpl.java