Kafka consumer couldn't receive serialize Object?

Question

So i want to implement simple application which send notification kafka producer to kafka consumer.So far i have successfully send String message to producer to consumer.But when i try to send notification object kafka consumer didn't receive any objects.This is the code i have used.

public class Notification implements Serializable{

    private String name;
    private String message;
    private long currentTimeStamp;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public long getCurrentTimeStamp() {
        return currentTimeStamp;
    }

    public void setCurrentTimeStamp(long currentTimeStamp) {
        this.currentTimeStamp = currentTimeStamp;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Notification that = (Notification) o;

        if (currentTimeStamp != that.currentTimeStamp) return false;
        if (message != null ? !message.equals(that.message) : that.message != null) return false;
        if (name != null ? !name.equals(that.name) : that.name != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + (message != null ? message.hashCode() : 0);
        result = 31 * result + (int) (currentTimeStamp ^ (currentTimeStamp >>> 32));
        return result;
    }

    @Override
    public String toString() {
        return "Notification{" +
                "name='" + name + '\'' +
                ", message='" + message + '\'' +
                ", currentTimeStamp=" + currentTimeStamp +
                '}';
    }
}

And this is producer

public class KafkaProducer {
    static String topic = "kafka-tutorial";


    public static void main(String[] args) {
        System.out.println("Start Kafka producer");
        Properties properties = new Properties();
        properties.put("metadata.broker.list", "localhost:9092");
        properties.put("serializer.class", "dev.innova.kafka.tutorial.producer.CustomSerializer");
        ProducerConfig producerConfig = new ProducerConfig(properties);
        kafka.javaapi.producer.Producer<String, Notification> producer = new kafka.javaapi.producer.Producer<String, Notification>(producerConfig);
        KeyedMessage<String, Notification> message = new KeyedMessage<String, Notification>(topic, createNotification());
        System.out.println("send Message to broker");
        producer.send(message);
        producer.close();

    }

    private static Notification createNotification(){
        Notification notification = new Notification();
        notification.setMessage("Sample Message");
        notification.setName("Sajith");
        notification.setCurrentTimeStamp(System.currentTimeMillis());
        return notification;
    }
}

And this is consumer

public class KafkaConcumer extends Thread {
    final static String clientId = "SimpleConsumerDemoClient";
    final static String TOPIC = "kafka-tutorial";
    ConsumerConnector consumerConnector;


    public KafkaConcumer() {
        Properties properties = new Properties();
        properties.put("zookeeper.connect","localhost:2181");
        properties.put("group.id","test-group");
        properties.put("serializer.class", "dev.innova.kafka.tutorial.producer.CustomSerializer");
        properties.put("zookeeper.session.timeout.ms", "400");
        properties.put("zookeeper.sync.time.ms", "200");
        properties.put("auto.commit.interval.ms", "1000");
        ConsumerConfig consumerConfig = new ConsumerConfig(properties);
        consumerConnector = Consumer.createJavaConsumerConnector(consumerConfig);
    }

    @Override
    public void run() {
        Map<String, Integer> topicCountMap = new HashMap<String, Integer>();
        topicCountMap.put(TOPIC, new Integer(1));
        Map<String, List<KafkaStream<byte[], byte[]>>> consumerMap = consumerConnector.createMessageStreams(topicCountMap);
        KafkaStream<byte[], byte[]> stream =  consumerMap.get(TOPIC).get(0);
        ConsumerIterator<byte[], byte[]> it = stream.iterator();
        System.out.println("It :" + it.size());
        while(it.hasNext()){
            System.out.println(new String(it.next().message()));
        }
    }

    private static void printMessages(ByteBufferMessageSet messageSet) throws UnsupportedEncodingException {
        for(MessageAndOffset messageAndOffset: messageSet) {
            ByteBuffer payload = messageAndOffset.message().payload();
            byte[] bytes = new byte[payload.limit()];
            payload.get(bytes);
            System.out.println(new String(bytes, "UTF-8"));
        }
    }
}

And finally i have used customserializer to serialize and deserialize object.

public class CustomSerializer implements Encoder<Notification>, Decoder<Notification> {
    public CustomSerializer(VerifiableProperties verifiableProperties) {
        /* This constructor must be present for successful compile. */
    }
    @Override
    public byte[] toBytes(Notification o) {
        return new byte[0];
    }

    @Override
    public Notification fromBytes(byte[] bytes) {
        return null;
    }
}

Can someone tell me what is the issue ? is this the right way ?

Answer 1

You have two problems.

First, your deserializer doesn't have any logic. It returns an empty byte array for each object it serializes and returns a null object whenever it's asked to deserialize an object. You need to put code there that actually serializes and deserializes your objects.

Second, if you plan to use the native JVM serialization and deserialization logic from the JVM, you'll need to add a serialVersionUID to your beans that will be transported. Something like this:

private static final long serialVersionUID = 123L;

You can use any value you like. When an object is deserialized by the JVM the serialVersionId in the object is compared to the value specified in the loaded class definition. If the two are different then the JVM assumes that even though you have a class definition loaded you don't have the correct version of the class definition loaded and serialization will fail. If you don't specify a value for serialVersionID in your class definition then the JVM will make one up for you and two different JVM's (the one with the producer and the one with the consumer) will almost certainly make up different values for you.

EDIT

You'd need to make your serializer look something like this if you want to leverage the default Java serialization:

public class CustomSerializer implements Encoder<Notification>, Decoder<Notification> {
    public CustomSerializer(VerifiableProperties verifiableProperties) {
        /* This constructor must be present for successful compile. */
    }

@Override
public byte[] toBytes(Notification o) {
    try {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(o);
        oos.close();
        byte[] b = baos.toByteArray();
        return b;
    } catch (IOException e) {
        return new byte[0];
    }
}

@Override
public Notification fromBytes(byte[] bytes) {
    try {
        return (Notification) new ObjectInputStream(new ByteArrayInputStream(b)).readObject();
    } catch (Exception e) {
        return null;
    }    
}

Answer 2

Create a custom deserializer , Kafka need a way to serialize and deserialize .We have to provide both of these implementations so far Need to add library to get the object mapper class

FasterXML jackson – 2.8.6

Example - serializer

public class PayloadSerializer implements org.apache.kafka.common.serialization.Serializer { @Override public byte[] serialize(String arg0, Object arg1) { byte[] retVal = null; ObjectMapper objectMapper = new ObjectMapper(); TestModel model =(TestModel) arg1; try { retVal = objectMapper.writeValueAsString(model).getBytes(); } catch (Exception e) { e.printStackTrace(); } return retVal; } @Override public void close() { } @Override public void configure(Map map, boolean bln) { } }

Deserializer

public class PayloadDeserializer implements Deserializer { @Override public void close() { } @Override public TestModel deserialize(String arg0, byte[] arg1) { ObjectMapper mapper = new ObjectMapper(); TestModel testModel = null; try { testModel = mapper.readValue(arg1, TestModel.class); } catch (Exception e) { e.printStackTrace(); } return testModel; } @Override public void configure(Map map, boolean bln) { } } public class PayloadDeserializer implements Deserializer { @Override public void close() { } @Override public TestModel deserialize(String arg0, byte[] arg1) { ObjectMapper mapper = new ObjectMapper(); TestModel testModel = null; try { testModel = mapper.readValue(arg1, TestModel.class); } catch (Exception e) { e.printStackTrace(); } return testModel; } @Override public void configure(Map map, boolean bln) { } } Finally we have to pass deserializer class to the receiver

ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG - PayloadDeserializer.class

or

deserializer.class - classpath.PayloadDeserializer

Answer 3

I strongly suggest you to convert your object to an Avro object before sending it.

It is not that difficult and is the Kafka way of transmitting objects.