IllegalArgumentException: Payload must not be null

[daroo]

Current implementation (1.0.2.RELEASE) of KafkaListener doesn't handle messages with null payload correctly. When a message with null payload comes in following exception is thrown:

java.lang.IllegalArgumentException: Payload must not be null
    at org.springframework.util.Assert.notNull(Assert.java:115)
    at org.springframework.messaging.support.MessageBuilder.createMessage(MessageBuilder.java:191)
    at org.springframework.kafka.support.converter.MessagingMessageConverter.toMessage(MessagingMessageConverter.java:78)
    at org.springframework.kafka.listener.adapter.MessagingMessageListenerAdapter.toMessagingMessage(MessagingMessageListenerAdapter.java:105)
    at org.springframework.kafka.listener.adapter.MessagingMessageListenerAdapter.onMessage(MessagingMessageListenerAdapter.java:97)
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeListener(KafkaMessageListenerContainer.java:597)
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.access$1800(KafkaMessageListenerContainer.java:222)
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer$ListenerInvoker.run(KafkaMessageListenerContainer.java:778)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.lang.Thread.run(Thread.java:745)

This happens even if the payload is marked as a @Payload(required = false).

Currently the only way to handle such messages is to create and register own implementation of a message converter.
However messages with null payload are completely valid in Kafka world (for example with a topic compaction enabled a message with a key and a null payload is treated as a delete from the log). Also KafkaTemplate support them correctly.

So, either remove notNull check for payload or use different converters depending on @Payload(required = true/false) flag... or at least provide a message converter implementation which accepts null payload.

[garyrussell]

Thanks; this is a bug - we're all at SpringOne Platform this week.

Contributions are always welcome 😄

[artembilan]

Looks like we can overcome (fix) the problem with empty string or byte[] - PayloadArgumentResolver:

if (isEmptyPayload(payload)) {
            if (ann == null || ann.required()) {
                String paramName = getParameterName(parameter);
                BindingResult bindingResult = new BeanPropertyBindingResult(payload, paramName);
                bindingResult.addError(new ObjectError(paramName, "Payload value must not be empty"));
                throw new MethodArgumentNotValidException(message, parameter, bindingResult);
            }
            else {
                return null;
            }
        }
...
    protected boolean isEmptyPayload(Object payload) {
        if (payload == null) {
            return true;
        }
        else if (payload instanceof byte[]) {
            return ((byte[]) payload).length == 0;
        }
        else if (payload instanceof String) {
            return !StringUtils.hasText((String) payload);
        }
        else {
            return false;
        }
    }

Although that solution in Spring Framework looks a bit clumsy for me...

[daroo]

I'd rather go with something like this - MessagingMessageConverter#toMessage:

return new KafkaMessage<>(extractAndConvertValue(record, type), kafkaMessageHeaders);
together with null check also in StringJsonMessageConverter#extractAndConvertValue
...where KafkaMessage is the same as GenericMessage but doesn't do null checks

I'd gladly contribute a code but I need a ticket in your bug tracking system I guess (or a branch should be named just GH-160?) 😄

BTW. I hope you guys enjoyed the conference. 😄

[artembilan]

Yeah! I think I can agree with you about "null-aware" KafkaMessage.

Yes, we are always open for contribution.
Yes, this issue is exactly a ticket in our system.
So, GH-160 is the best name for branch to Pull Request eventually.

Thank you for catching that up and for considering contribution!

[daroo]

I've created PR: #163