Avro无法使用更新的架构反序列化消息

Question

I have a schema which has been updated to include a new field. I'm using avro reflection and the confluent schema registry to deserialize/serialize data like so:

Serialization:

Schema schema = REFLECT_DATA.getSchema(value.getClass());
try {
    int registeredSchemaId = this.schemaRegistry.register(subject, schema);

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    out.write(0);
    out.write(ByteBuffer.allocate(4).putInt(registeredSchemaId).array());

    DatumWriter<Object> dw = new ReflectDatumWriter<>(schema);
    Encoder encoder = ENCODER_FACTORY.directBinaryEncoder(out, null);
    dw.write(value, encoder);
    encoder.flush();
    return out.toByteArray();
} catch (RuntimeException | IOException e) {
    throw new SerializationException("Error serializing Avro message", e);
} catch (RestClientException e) {
    throw new SerializationException("Error registering Avro schema: " + schema, e);
}

Deserialization:

if (readerSchema == null) {
    readerSchema = new Schema.Parser().parse(schemaString);
}

int schemaId = -1;
try {
    ByteBuffer buffer = ByteBuffer.wrap(payload);
    if (buffer.get() != MAGIC_BYTE) {
        throw new SerializationException("Unknown magic byte!");
    }

    schemaId = buffer.getInt();
    Schema writerSchema = schemaRegistry.getById(schemaId);

    int start = buffer.position() + buffer.arrayOffset();
    int length = buffer.limit() - 1 - idSize;
    DatumReader<Object> reader = new ReflectDatumReader<>(writerSchema, readerSchema);
    BinaryDecoder decoder = decoderFactory.binaryDecoder(buffer.array(), start, length, null);
    return reader.read(null, decoder);  //line 83
} catch (IOException e) {
    throw new SerializationException("Error deserializing Avro message for id " + schemaId, e);
} catch (RestClientException e) {
    throw new SerializationException("Error retrieving Avro schema for id " + schemaId, e);
}

The schema is defined by a scala case class, the old one looks like this:

case class Data(oldField: String) {
    def this("")
}

and it has been updated like so:

case class Data(oldField: String, @AvroDefault("") newField: String) {
    def this("", "")
}

However, deserializing sometimes throws an AvroTypeException with the following stack:

Caused by: org.apache.avro.AvroTypeException: Found com.company.project.DataHolder$.Data, expecting com.company.project.DataHolder$.Data
    at org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:231)
    at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
    at org.apache.avro.io.ResolvingDecoder.readFieldOrder(ResolvingDecoder.java:127)
    at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:173)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:148)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:139)
    at io.fama.pubsub.KafkaAvroReflectDeserializer.deserialize(KafkaAvroReflectDeserializer.java:83)

Which I think is caused by difficulties serializing old messages (but am not entirely sure - I just can't reason as to what else it could be). Has anyone else ever experienced this error or does anyone have any ideas to fix it?

Answer 1

如果您正在使用org.apache.avro.reflect属性，那么我认为您不能使用Scala案例类 - Scala案例类参数是不可变的，我相信属性映射器需要有一个公共类空构造函数和java可见字段，甚至可能是@BeanProperty来生成java setter / getters。