The main interface to provide the Topology to be executed

The concept of Topology is not specific to Azkarra but is fundamental in the implementation of a Kafka Streams application. A Topology is an object that is part of the public Kafka Streams API and allows you to define all the operations (i.e stateless or stateful) to be performed on one or more input Kafka topics.

1 The TopologyProvider interface

In Azkarra Streams, a Topology object must be defined and provided through the implementation of the TopologyProvider interface.

Here is a simple example :

    public class WordCountTopology implements TopologyProvider {

        public Topology topology() {                       
            StreamsBuilder builder = new StreamsBuilder();
            KStream<String, String> textLines = 

                .flatMapValues(value ->
                .groupBy((key, value) -> value)
                   Produced.with(Serdes.String(), Serdes.Long())

        public String version() {
            return "1.0";

One of the specificities of Azkarra is that the TopologyProvider interface requires you to provide a non-null topology version. Usually, you will return the version of your project (e.g: 1.0, 1.2-SNAPSHOT, etc).

Last modified March 3, 2021: docs(site): update docs for 0.9.x (ca3e155b)