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

WireFormatAvroConsumer.java

/*
 * This file is part of Wire Format Consumer 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.IOException;
import java.nio.ByteBuffer;
import java.util.Base64;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.Decoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.specific.SpecificDatumReader;

/**
 * Basic requirements for pom.xml setup.
 *     Java JDK: >=9 (Tested with 21)
 * Dependencies: org.apache.avro:avro:1.12.1
 *      Plugins: org.apache.avro:avro-maven-plugin:1.12.1
 */
public class WireFormatAvroConsumer {

    public static void main(String[] args) throws IOException {
        /**
         * Alternative (Raw Bytes):
         * byte[] message = { 0x00, 0x00, 0x00, 0x00, 0x01, 0x18, 0x48, 0x65, 0x6c, 
         *                    0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x21 };
         */
        byte[] message = Base64.getDecoder().decode("AAAAAAEYSGVsbG8gV29ybGQh");
        
        ByteBuffer buffer = ByteBuffer.wrap(message);
        byte magicByte = buffer.get();   // Position goes from 0 -> 1.
        int schemaId = buffer.getInt();  // Reads bytes [1..4], position goes from 1 -> 5.
        
        int remainingBytes = buffer.remaining();
        byte[] avroPayload = new byte[remainingBytes];
        buffer.get(avroPayload); // Writes remaining bytes to byte array.
        
        // Requires class to be generated from avro schema using avro-maven-plugin.
        DatumReader<Greeting> reader = new SpecificDatumReader<>(Greeting.class);
        Decoder decoder = DecoderFactory.get().binaryDecoder(avroPayload, null);
        Greeting greeting = reader.read(null, decoder);

        System.out.println("Magic: " + magicByte);
        System.out.println("Schema ID: " + schemaId);
        System.out.println("Payload [Message Field]: " + greeting.getMessage());
    }
}