How to debug kafkastreams code?

Question

Has anyone managed to debug kafkastreams code written in Java 8 using IntelliJ IDEA?. I am running a simple linesplit.java code where it takes stream from one topic and splits it and sends it to another topic, but I have no idea where to keep the debug pointer to debug every message as it flows through linesplit.java.

Linesplit.java

public static void main(String[] args) throws Exception {
    Properties props = new Properties();
    props.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-linesplit");
    props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
    props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
    props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

    final StreamsBuilder builder = new StreamsBuilder();



    // ------- use the code below for Java 8 and uncomment the above ---

    builder.stream("streams-input")
           .flatMapValues(value -> Arrays.asList(value.toString().split("\\W+")))
           .to("streams-output");

     //  -----------------------------------------------------------------

    final Topology topology = builder.build();
    final KafkaStreams streams = new KafkaStreams(topology, props);
    final CountDownLatch latch = new CountDownLatch(1);

    // attach shutdown handler to catch control-c
    Runtime.getRuntime().addShutdownHook(new Thread("streams-shutdown-hook") {
        @Override
        public void run() {
            streams.close();
            latch.countDown();
        }
    });

    try {
        streams.start();
        latch.await();
    } catch (Throwable e) {
        System.exit(1);
    }
    System.exit(0);
}

Answer 1

Did you try peek?

Your example can be as follows (using peek function):

builder
       .stream("streams-input")
       .peek((k, v) -> log.info("Observed event: {}", v))
       .flatMapValues(value -> Arrays.asList(value.toString().split("\\W+"))).
       .peek((k, v) -> log.info("Transformed event: {}", v))
       .to("streams-output");

I didn't run the code but this is how I do it normally.