Example showing how a Kafka producer can send an Avro message using Confluent Wire Format without integrating with the Schema Registry.

WireFormatAvroProducer.java

/*
 * This file is part of Wire Format Producer Gist <https://github.com/StevenJDH>.
 * Copyright (c) 2025 Steven Jenkins De Haro
 * 
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree or at
 * https://opensource.org/licenses/MIT.
 */

package io.github.stevenjdh.examples.avro;

import com.example.messages.Greeting;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Base64;
import java.util.HexFormat;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.EncoderFactory;
import org.apache.avro.specific.SpecificDatumWriter;

/**
 * Basic requirements for pom.xml setup.
 *     Java JDK: >=17 or >=9 without HexFormat (Tested with 21)
 * Dependencies: org.apache.avro:avro:1.12.1
 *      Plugins: org.apache.avro:avro-maven-plugin:1.12.1
 */
public class WireFormatAvroProducer {

    public static void main(String[] args) throws IOException {
        Greeting greeting = new Greeting("Hello World!");
        
        byte magicByte = 0x00;
        int schemaId = 1;
        byte[] avroPayload;
        
        try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
            DatumWriter<Greeting> writer = new SpecificDatumWriter<>(greeting.getSchema());
            Encoder encoder = EncoderFactory.get().binaryEncoder(out, null);
            
            writer.write(greeting, encoder);
            encoder.flush();
            avroPayload = out.toByteArray(); // Serialize it to a byte array.
        }

        // Prepend the wire format.
        ByteBuffer buffer = ByteBuffer.allocate(1 + 4 + avroPayload.length);
        buffer.put(magicByte);
        buffer.putInt(schemaId);
        buffer.put(avroPayload);

        // Ready for sending as a native-based Kafka client.
        byte[] message = buffer.array();
        // Ready for sending as a REST-based Kafka client.
        String base64Message= Base64.getEncoder().encodeToString(message);
        // Just to show the hex representation.
        String hexMessage = HexFormat.ofDelimiter(" ").formatHex(message);

        System.out.println("Avro Payload Length: " + avroPayload.length);
        System.out.println("Message Length: " + message.length);
        System.out.println("Message (base64): " + base64Message);
        System.out.println("Message (hex): " + hexMessage);
    }
}