Kafka streams Consumer not getting the messages. Word Count Example

Question

This is the code that I have written for a simple word count Application using kafka. I tried to run the code but my consumer doesnt seem to pick up any messages. I dont understand the error in my code.

I have created both the topics, and verified it by listing the topics.

Java version: 11 Kafka version: 2.11-2.1.0 Zookeeper Version: 3.4.13

public static final String INPUT_TOPIC = "streams-plaintext-input";
    public static final String OUTPUT_TOPIC = "streams-wordcount-output";

    static void createWordCountStream(final StreamsBuilder builder) {
        final KStream<String, String> source = builder.stream(INPUT_TOPIC);

        final KTable<String, Long> counts = source
                .flatMapValues(value -> Arrays.asList(value.toLowerCase(Locale.getDefault()).split("\\W+")))
                .groupBy((key, value) -> value)
                .count();

        counts.toStream().to(OUTPUT_TOPIC, Produced.with(Serdes.String(), Serdes.Long()));
    }

    public static void main(final String[] args) throws IOException {
        final Properties props = new Properties();
        props.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-wordcount");
        props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        props.put(StreamsConfig.CACHE_MAX_BYTES_BUFFERING_CONFIG, 0);
        props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
        props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());

        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

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

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

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

Answer 1

The code works fine. I just restarted zookeeper and the server and it came back up again.