Bill Bejeck has built a simple Kafka Streams application for us:
This blog post will quickly get you off the ground and show you how Kafka Streams works. We’re going to make a toy application that takes incoming messages and upper-cases the text of those messages, effectively yelling at anyone who reads the message. This application is called the yelling application.
Before diving into the code, let’s take a look at the processing topology you’ll assemble for this “yelling” application. We’ll build a processing graph topology, where each node in the graph has a particular function.
His entire application is 20 lines of code but it does function as a valid Kafka Streams app and works well as a demo.