KafkaAvroDeserializer does not return SpecificRecord but returns GenericRecord

Question

My KafkaProducer is able to use KafkaAvroSerializer to serialize objects to my topic. However, KafkaConsumer.poll() returns deserializ

Answer 1

Edit : reflect data support got merged (see below)

To add to Chin Huang's answer, for minimal code and better performance, you should probably implement it this way :

/**
 * Extends deserializer to support ReflectData.
 *
 * @param <V>
 *     value type
 */
public abstract class SpecificKafkaAvroDeserializer<V extends SpecificRecordBase> extends AbstractKafkaAvroDeserializer implements Deserializer<V> {
  private final Schema schema;
  private Class<T> type;
  private DecoderFactory decoderFactory = DecoderFactory.get();

  protected SpecificKafkaAvroDeserializer(Class<T> type, Map<String, ?> props) {
    this.type = type;
    this.schema = ReflectData.get().getSchema(type);
    this.configure(this.deserializerConfig(props));
  }

  public void configure(Map<String, ?> configs) {
    this.configure(new KafkaAvroDeserializerConfig(configs));
  }

  @Override
  protected T deserialize(
          boolean includeSchemaAndVersion,
          String topic,
          Boolean isKey,
          byte[] payload,
          Schema readerSchemaIgnore) throws SerializationException {

    if (payload == null) {
      return null;
    }

    int schemaId = -1;
    try {
      ByteBuffer buffer = ByteBuffer.wrap(payload);
      if (buffer.get() != MAGIC_BYTE) {
        throw new SerializationException("Unknown magic byte!");
      }

      schemaId = buffer.getInt();
      Schema schema = schemaRegistry.getByID(schemaId);

      Schema readerSchema = ReflectData.get().getSchema(type);

      int start = buffer.position() + buffer.arrayOffset();
      int length = buffer.limit() - 1 - idSize;
      SpecificDatumReader<T> reader = new SpecificDatumReader(schema, readerSchema);
      BinaryDecoder decoder = decoderFactory.binaryDecoder(buffer.array(), start, length, null);
      return reader.read(null, decoder);
    } catch (IOException e) {
      throw new SerializationException("Error deserializing Avro message for id " + schemaId, e);
    } catch (RestClientException e) {
      throw new SerializationException("Error retrieving Avro schema for id " + schemaId, e);
    }
  }
}

Answer 2

KafkaAvroDeserializer supports SpecificData

It's not enabled by default. To enable it:

properties.put(KafkaAvroDeserializerConfig.SPECIFIC_AVRO_READER_CONFIG, true);

KafkaAvroDeserializer does not support ReflectData

Confluent's KafkaAvroDeserializer does not know how to deserialize using Avro ReflectData. I had to extend it to support Avro ReflectData:

/**
 * Extends deserializer to support ReflectData.
 *
 * @param <V>
 *     value type
 */
public abstract class ReflectKafkaAvroDeserializer<V> extends KafkaAvroDeserializer {

  private Schema readerSchema;
  private DecoderFactory decoderFactory = DecoderFactory.get();

  protected ReflectKafkaAvroDeserializer(Class<V> type) {
    readerSchema = ReflectData.get().getSchema(type);
  }

  @Override
  protected Object deserialize(
      boolean includeSchemaAndVersion,
      String topic,
      Boolean isKey,
      byte[] payload,
      Schema readerSchemaIgnored) throws SerializationException {

    if (payload == null) {
      return null;
    }

    int schemaId = -1;
    try {
      ByteBuffer buffer = ByteBuffer.wrap(payload);
      if (buffer.get() != MAGIC_BYTE) {
        throw new SerializationException("Unknown magic byte!");
      }

      schemaId = buffer.getInt();
      Schema writerSchema = schemaRegistry.getByID(schemaId);

      int start = buffer.position() + buffer.arrayOffset();
      int length = buffer.limit() - 1 - idSize;
      DatumReader<Object> reader = new ReflectDatumReader(writerSchema, readerSchema);
      BinaryDecoder decoder = decoderFactory.binaryDecoder(buffer.array(), start, length, null);
      return reader.read(null, decoder);
    } catch (IOException e) {
      throw new SerializationException("Error deserializing Avro message for id " + schemaId, e);
    } catch (RestClientException e) {
      throw new SerializationException("Error retrieving Avro schema for id " + schemaId, e);
    }
  }
}

Define a custom deserializer class which deserializes to MyBean:

public class MyBeanDeserializer extends ReflectKafkaAvroDeserializer<MyBean> {
  public MyBeanDeserializer() {
    super(MyBean.class);
  }
}

Configure KafkaConsumer to use the custom deserializer class:

properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, MyBeanDeserializer.class);