Getting java.lang.ClassCastException: [B cannot be cast to org.springframework.messaging.Message exception after consuming batch

Question

I am using spring-cloud-stream-kafka-binder-3.0.4 to consume the messages in batch, after consuming, converting the Message into object but getting the above exception.

Here is the code:

@StreamListener(ActivityChannel.ACTIVITY_INPUT_CHANNEL)
public void handleActivity(List<Message<Event>> messages,
    @Header(name = "deliveryAttempt", defaultValue = "1") int deliveryAttempt,
    @Header(KafkaHeaders.ACKNOWLEDGMENT) Acknowledgment acknowledgment)  
{
    try
    {
        log.info("Received activity message with message length {} attempt {}",
              messages.size(), deliveryAttempt);
        List<Event> eventList = messages.stream().map(Message::getPayload).collect(Collectors.toList());
        nodeConfigActivityBatchProcessor.processNodeConfigActivity(eventList);
        acknowledgment.acknowledge();
        log.debug("Processed activity message {} successfully!!", messages.size());
    } 
    catch (Exception e)
    { 
        throw e;
    }
}

Configuration:

spring.cloud.stream.bindings.activity-input-channel.destination=TOPIC.FEED.NAME
spring.cloud.stream.bindings.activity-input-channel.contentType=application/json
spring.cloud.stream.bindings.activity-input-channel.consumer.batch-mode=true
spring.cloud.stream.bindings.activity-input-channel.consumer.max-attempts=1
spring.cloud.stream.kafka.bindings.activity-input-channel.consumer.auto-commit-offset=false
spring.cloud.stream.kafka.bindings.activity-input-channel.consumer.reset-offsets=true
spring.cloud.stream.kafka.bindings.activity-input-channel.consumer.start-offset=latest
spring.kafka.consumer.max-poll-records=5
spring.kafka.consumer.fetch-max-wait=60000
spring.kafka.consumer.fetch-min-size=500

I get the above error at this line List<Event> eventList = messages.stream().map(Message::getPayload).collect(Collectors.toList()); at .collect(Collectors.toList()). I am not able to figure out why??

if I check Message<Event> eventMessage = messages.get(0) getting the same exception(messages is the list of Message variable).

if batch mode if false then it only consume a single message handleActivity(Message message), then it works fine, no exception.

Is there any deserializer needs to be added when using batch mode???

that message means you are trying to cast an instance of B to an instance of Message, but there is no IS-A relationship between the two, which is why it fails. — Stultuske, Sep 17 '21 at 09:16
I publish messages to kafka producer, and this listener consume in batch of 5, but after that I am not able to get the first element from the list it received (Which is of Message format). Same way, if batch mode if false then it only consume a single message handleActivity(Message message), then it works fine. what is B type , I don't understand — APK, Sep 17 '21 at 09:22
I don't know what B is neither, but that is the type mentioned in your error message — Stultuske, Sep 17 '21 at 09:26

APK · Accepted Answer · 2021-10-01T08:52:01.307

I managed to solve this Exception, by adding a Deserialiser.

So Below is my batch Listener, Instead of consuming List<Message<Event>> messages as mentioned in the question, consuming List<Event> messages.

@StreamListener(ActivityChannel.ACTIVITY_INPUT_CHANNEL)
 public void handleActivity(List<Event> messages,@Header(KafkaHeaders.ACKNOWLEDGMENT) Acknowledgment acknowledgment)  
 {
  try
  {
    log.info("Received activity message with message length {} attempt 
    {}",messages.size(), deliveryAttempt);        
   nodeConfigActivityBatchProcessor.processNodeConfigActivity(messages);
    acknowledgment.acknowledge();
    log.debug("Processed activity message {} successfully!!", 
   messages.size());
 } 
 catch (Exception e)
  { 
      throw e;
  }
}

Added the below Deserialiser

public class EventDeserializer extends JsonDeserializer<Event> {
}

Added below value.deserializer property to properties file.

spring.cloud.stream.kafka.bindings.input-channel.consumer.configuration.value.deserializer=com.sample.messaging.util.EventDeserializer

I got list of events in my batch listener.

score 1 · Answer 2 · answered Apr 04 '22 at 09:57

It is not mentioned anywhere unfortunately :-(, but to wrap input events into org.springframework.messaging.Message (to get record keys for example), here is the correct signature when doing batch processing:

@Bean
public Consumer<Message<List<String>>> sink() {
    return messages -> {
        List<?> keys = messages.getHeaders().get(KafkaHeaders.RECEIVED_MESSAGE_KEY, List.class);
        log.info("headers {}", messages.getHeaders());
        keys.forEach(k -> log.info("key {}", k));
        messages.getPayload().forEach(string -> log.info("processing {}", string));
    };
}

You notice that is the signed the other way around: Message<List<?>> rather than List<Message<?>>!

Getting java.lang.ClassCastException: [B cannot be cast to org.springframework.messaging.Message exception after consuming batch

2 Answers2