Kafka error deserializing key/value for partition

Question

I've got an integration tests that passes when I send to a Kafka topic without a key. However, when I add a key I start to get serialization errors.

org.apache.kafka.common.errors.SerializationException: Error deserializing key/value for partition topic-1 at offset 0

Caused by: org.apache.kafka.common.errors.SerializationException: Size of data received by IntegerDeserializer is not 4

This is my sender class:

public class Sender {
    private static final Logger LOG = LoggerFactory.getLogger(Sender.class);

    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;

    public void send() {

        String topic = "topic";
        String data = "data";
        String key = "key";

        LOG.info("sending to topic: '{}', key: '{}', data: '{}'", topic, key, data);

        // does not work
        kafkaTemplate.send(topic, key, data);

        // works
        // kafkaTemplate.send(topic, data);

    }
}

This is my configuration, where I specify a StringSerializer for the key

@Configuration
@EnableKafka
public class Config {

    @Bean
    public Sender sender() {
        return new Sender();
    }

    @Bean
    public Properties properties() {
        return new Properties();
    }

    @Bean
    public Map<String, Object> producerConfigs(Properties properties) {
        Map<String, Object> props = new HashMap<>();
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, properties.getBootstrapServers());
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        return props;
    }

    @Bean
    public ProducerFactory<String, String> producerFactory(Properties properties) {
        return new DefaultKafkaProducerFactory<>(producerConfigs(properties));
    }

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate(Properties properties) {
        return new KafkaTemplate<>(producerFactory(properties));
    }

}

The problem may related to the message listener in my test, but that is also using strings across the board

@RunWith(SpringRunner.class)
@SpringBootTest()
@DirtiesContext
public class SenderIT {


    public static final Logger LOG = LoggerFactory.getLogger(SenderIT.class);

    private static String SENDER_TOPIC = "topic";

    @Autowired
    private Sender sender;

    private KafkaMessageListenerContainer<String, String> container;

    private BlockingQueue<ConsumerRecord<String, String>> records;

    @ClassRule
    public static KafkaEmbedded embeddedKafka = new KafkaEmbedded(1, true, SENDER_TOPIC);

    @Before
    public void setUp() throws Exception {

        // set up the Kafka consumer properties
        Map<String, Object> consumerProperties =
            KafkaTestUtils.consumerProps("sender", "false", embeddedKafka);

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

        // create a Kafka consumer factory
        DefaultKafkaConsumerFactory<String, String> consumerFactory =
            new DefaultKafkaConsumerFactory<String, String>(consumerProperties);

        // set the topic that needs to be consumed
        ContainerProperties containerProperties = new ContainerProperties(SENDER_TOPIC);

        // create a Kafka MessageListenerContainer
        container = new KafkaMessageListenerContainer<>(consumerFactory, containerProperties);

        // create a thread safe queue to store the received message
        records = new LinkedBlockingQueue<>();

        // setup a Kafka message listener
        container.setupMessageListener(new MessageListener<String, String>() {
        @Override
        public void onMessage(ConsumerRecord<String, String> record) {
            LOG.debug("test-listener received message='{}'", record.toString());
            records.add(record);
        }
        });

        // start the container and underlying message listener
        container.start();

        // wait until the container has the required number of assigned partitions
        ContainerTestUtils.waitForAssignment(container, embeddedKafka.getPartitionsPerTopic());
    }

    @After
    public void tearDown() {
        // stop the container
        container.stop();
    }

    @Test
    public void test() throws InterruptedException {

        sender.send();

        // check that the message was received in Kafka
        ConsumerRecord<String, String> kafkaTopicMsg = records.poll(10, TimeUnit.SECONDS);

        LOG.debug("kafka recieved = {}", kafkaTopicMsg);

        assertThat(kafkaTopicMsg).isNotNull();

    }

}

As always, any help would be appreciated.

All the code to reproduce is available at https://github.com/LewisWatson/kafka-embedded-test/tree/8322621ad4e302d982e5ecd28af9fd314696d850

Full stack trace is available at https://travis-ci.org/LewisWatson/kafka-embedded-test/builds/273227986

Answer 1

After further inspection of the logs I was able to narrow the problem down to the test message listener

2017-09-08 09:30:06.845 ERROR 2550 --- [           -C-1] essageListenerContainer$ListenerConsumer : Container exception

org.apache.kafka.common.errors.SerializationException: Error deserializing key/value for partition topic-1 at offset 0

Caused by: org.apache.kafka.common.errors.SerializationException: Size of data received by IntegerDeserializer is not 4

https://travis-ci.org/LewisWatson/kafka-embedded-test/builds/273227986#L2961

It looks like its expecting the key to be an integer for some reason.

Explicitly setting string deserializers for the consumer factory fixed the problem.

// create a Kafka consumer factory
DefaultKafkaConsumerFactory<String, String> consumerFactory =
    new DefaultKafkaConsumerFactory<String, String>(consumerProperties,
        new StringDeserializer(), new StringDeserializer());