AvroTest.java

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import org.apache.avro.Schema;
import org.apache.avro.generic.GenericData;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.generic.GenericRecordBuilder;
import org.apache.avro.io.BinaryDecoder;
import org.apache.avro.io.BinaryEncoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.io.EncoderFactory;

public class AvroTest {
    public static Schema WRITER_SCHEMA = new Schema.Parser().parse("{" +
        "\"namespace\": \"com.martinkl.avro\", " +
        "\"type\": \"record\", " +
        "\"name\": \"Test\", " +
        "\"fields\": [" +
            "{\"name\": \"enumTest\", \"type\": " +
            "{\"type\": \"enum\", \"name\": \"EnumTest\", \"symbols\": [\"ONE\", \"TWO\", \"THREE\", \"FOUR\"]}}" +
        "]}");

    public static Schema READER_SCHEMA = new Schema.Parser().parse("{" +
        "\"namespace\": \"com.martinkl.avro\", " +
        "\"type\": \"record\", " +
        "\"name\": \"Test\", " +
        "\"fields\": [" +
            "{\"name\": \"enumTest\", \"type\": " +
            "{\"type\": \"enum\", \"name\": \"EnumTest\", \"symbols\": [\"ONE\", \"TWO\", \"THREE\"]}}, " +
            "{\"name\": \"newField\", \"type\": [\"null\", \"string\"], \"default\": null}" +
        "]}");

    public static int main(String[] args) throws IOException {
        Schema enumType = READER_SCHEMA.getField("enumTest").schema();
        GenericData.Record record = new GenericRecordBuilder(WRITER_SCHEMA)
                .set("enumTest", new GenericData.EnumSymbol(enumType, "ONE"))
                .build();
        System.out.println("Before encoding: " + record);

        // Encode the record with the writer schema
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        BinaryEncoder encoder = EncoderFactory.get().binaryEncoder(output, null);
        new GenericDatumWriter<>(WRITER_SCHEMA).write(record, encoder);
        encoder.flush();

        // Decode the record with the reader schema
        BinaryDecoder decoder = DecoderFactory.get().binaryDecoder(output.toByteArray(), null);
        Object obj = new GenericDatumReader<>(WRITER_SCHEMA, READER_SCHEMA).read(null, decoder);
        System.out.println("After decoding: " + obj);
        return 0;
    }
}