Kafka Serialization of an object [duplicate] - serialization

Question

This question already has answers here:
Writing Custom Kafka Serializer
(3 answers)
Closed 2 years ago.
I started playing with Kafka. I've set an a zookeeper configuration, and I managed to send and consume String messages.
Now I am trying to pass an Object (in java), but from some reason, when parsing the Message in the consumer I have header issues. I tried several serialization options (using Decoder/Encoder), and all of the return the same header issue.
Here is my code
The producer:
Properties props = new Properties();
props.put("zk.connect", "localhost:2181");
props.put("serializer.class", "com.inneractive.reporter.kafka.EventsDataSerializer");
ProducerConfig config = new ProducerConfig(props);
Producer<Long, EventDetails> producer = new Producer<Long, EventDetails>(config);
ProducerData<Long, EventDetails> data = new ProducerData<Long, EventDetails>("test3", 1, Arrays.asList(new EventDetails());
try {
producer.send(data);
} finally {
producer.close();
}
And the consumer:
Properties props = new Properties();
props.put("zk.connect", "localhost:2181");
props.put("zk.connectiontimeout.ms", "1000000");
props.put("groupid", "test_group");
// Create the connection to the cluster
ConsumerConfig consumerConfig = new ConsumerConfig(props);
ConsumerConnector consumerConnector = Consumer.createJavaConsumerConnector(consumerConfig);
// create 4 partitions of the stream for topic “test”, to allow 4 threads to consume
Map<String, List<KafkaMessageStream<EventDetails>>> topicMessageStreams =
consumerConnector.createMessageStreams(ImmutableMap.of("test3", 4), new EventsDataSerializer());
List<KafkaMessageStream<EventDetails>> streams = topicMessageStreams.get("test3");
// create list of 4 threads to consume from each of the partitions
ExecutorService executor = Executors.newFixedThreadPool(4);
// consume the messages in the threads
for (final KafkaMessageStream<EventDetails> stream: streams) {
executor.submit(new Runnable() {
public void run() {
for(EventDetails event: stream) {
System.err.println("********** Got message" + event.toString());
}
}
});
}
and my Serializer:
public class EventsDataSerializer implements Encoder<EventDetails>, Decoder<EventDetails> {
public Message toMessage(EventDetails eventDetails) {
try {
ObjectMapper mapper = new ObjectMapper(new SmileFactory());
byte[] serialized = mapper.writeValueAsBytes(eventDetails);
return new Message(serialized);
} catch (IOException e) {
e.printStackTrace();
return null; // TODO
}
}
public EventDetails toEvent(Message message) {
EventDetails event = new EventDetails();
ObjectMapper mapper = new ObjectMapper(new SmileFactory());
try {
//TODO handle error
return mapper.readValue(message.payload().array(), EventDetails.class);
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
}
And this is the error I get:
org.codehaus.jackson.JsonParseException: Input does not start with Smile format header (first byte = 0x0) and parser has REQUIRE_HEADER enabled: can not parse
at [Source: N/A; line: -1, column: -1]
When I worked with MessagePack and with plain writing to a ObjectOutputStream I got a similiar header issue. I also tried to add the payload CRC32 to the message, but that didn't help as well.
What am I doing wrong here?

Answer 1

Hm, I haven't run into the same header issue that you are encountering but my project wasn't compiling correctly when I didn't provide a VerifiableProperties constructor in my encoder/decoder. It seems strange that the missing constructor would corrupt Jackson's deserialization though.
Perhaps try splitting up your encoder and decoder and include the VerifiableProperties constructor in both; you shouldn't need to implement Decoder[T] for serialization. I was able to successfully implement json de/serialization using ObjectMapper following the format in this post.
Good luck!

Answer 2

Bytebuffers .array() method is not very reliable. It depends on the particular implementation. You might want to try
ByteBuffer bb = message.payload()
byte[] b = new byte[bb.remaining()]
bb.get(b, 0, b.length);
return mapper.readValue(b, EventDetails.class)