Processor is both Producer and Consumer. It consumes the data from 1 topic and produces data for another topic.

In our case, we have to do the following

consume the data from numbers topic

remove the odd numbers

squares the even number

write back into another topic.

Lets create the processor by using the corresponding Functional Interface in Java which is Function.

We consume the data which is KStream

We do some processing

Then we return the KStream. Do note that the return type could be anything. Does not have to be same as Input type.