如何使用 Producer 将自定义对象发送到 Kafka Topic

Question

I would like to send my Account class with Producer to my Kafka Topic, then I will aggregate with Kafka Stream. However, I can not send Object I am getting error :

Caused by: org.apache.kafka.common.KafkaException: bank.Account is not an instance of org.apache.kafka.common.serialization.Serializer

My Producer class:

 public static void main(String[] args) {

        DataAccess dataAccess = new DataAccess();
        List<Account> accountList = dataAccess.read();

        final Logger logger = LoggerFactory.getLogger(Producer.class);
        Properties properties = new Properties();

        properties.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,"127.0.0.1:9092");
        properties.setProperty(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,LongSerializer.class.getName());
        properties.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,Account.class.getName());


        KafkaProducer<Long,Account> producer = new KafkaProducer<Long, Account>(properties);



        for (Account account : accountList) {

            ProducerRecord<Long,Account> record = new ProducerRecord<Long, Account>("bank_account",account.getFromId(),account);


            producer.send(record, new Callback() {
                public void onCompletion(RecordMetadata recordMetadata, Exception e) {
                    if (e == null) {
                        logger.info("Record sent successfully. \n "+ "Topic : "+recordMetadata.topic() +"\n"+
                                "Partition : " + recordMetadata.partition() + "\n"+
                                "Offset : " +recordMetadata.offset() +"\n"+
                                "Timestamp: " +recordMetadata.timestamp() +"\n");
                        try {
                            Thread.sleep(1000);
                        } catch (InterruptedException e1) {
                            e1.printStackTrace();
                        }

                    }
                    else{
                        logger.info("Error sending producer");
                    }
                }
            });
        }


        producer.flush();
        producer.close();
    }

It gives error in this line :

KafkaProducer<Long,Account> producer = new KafkaProducer<Long, Account>(properties);

My Account class:

public class Account {

    private long fromId;
    private long amount;
    private long toId;
    private ZonedDateTime time;
}

So my question is, how can we send custom object to kafka topics? After that I want to consume that message of course.

Answer 1

This line

properties.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,Account.class.getName());

You must implement your own Serializer class . It cannot be a plain class.

---

Some people use JSON to serialize, others use Avro or Protobuf. However you get the data into a byte[] is just an implementation detail.

• Java Kafka Object serilizer and deserializer

Answer 2

//1 
prop.setProperty(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
        prop.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, Employee.class.getName());

//2
 KafkaProducer<String, Employee> producer = new KafkaProducer(prop);

        Employee emp = new Employee(1, "Arun");

        ProducerRecord prodRecord = new ProducerRecord("aryan_topic", emp);
//3
import org.apache.kafka.common.header.Headers;
import org.apache.kafka.common.serialization.Serializer;

import java.io.Serializable;
import java.util.Map;

//Developed by Arun Singh
public class Employee implements Serializable, Serializer {
    Integer empId;
    String empName;
    Address add;

    public Employee() {
    }

    public Employee(Integer empId, String empName, Address add) {
        this.empId = empId;
        this.empName = empName;
        this.add = add;
    }

    public Integer getEmpId() {
        return empId;
    }

    public String getEmpName() {
        return empName;
    }

    public Address getAdd() {
        return add;
    }

    public void setEmpId(Integer empId) {
        this.empId = empId;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    public void setAdd(Address add) {
        this.add = add;
    }

    public void configure(Map configs, boolean isKey) {

    }

    public byte[] serialize(String s, Object o) {
        return new byte[0];
    }

    public byte[] serialize(String topic, Headers headers, Object data) {
        return new byte[0];
    }

    public void close() {

    }
}