KStream -- iterate LIST of values and send it to output topic

Question

I have a below scenario

KStream<String List<Foo> > fooList = returns me this KStream;

now I have to send this to outputTopic one by one rather than a whole list (i.e) fooList iterate the values alone and push them to the destination topic, so that Individual messages are pushed

Answer 1

I believe this will work: fooList.flatMapValues(v -> v).to("output");

You can read more about flatMapValues here: https://kafka.apache.org/31/javadoc/org/apache/kafka/streams/kstream/KStream.html#flatMapValues(org.apache.kafka.streams.kstream.ValueMapperWithKey).

From a mathematical point of view, you asking how to flatten the KStream of a List<Foo>. Since flatten is the same as the flatMap of the identify function, this ought to be what you want.