Spring Integration Kafka - Sending a basic String - spring-integration

Question

I am trying to send a basic String payload using Spring Integration Kafka v1.2.1, but it's failing with the following exception:
2015-09-03 11:50:39.729 ERROR 14418 --- [task-executor-3] [ ] o.s.integration.handler.LoggingHandler : org.springframework.messaging.MessageHandlingException: error occurred in message handler [org.springframework.integration.kafka.outbound.KafkaProducerMessageHandler#0]; nested exception is org.apache.kafka.common.errors.SerializationException: Can't convert value of class [B to class org.apache.kafka.common.serialization.StringSerializer specified in value.serializer
at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:84)
at org.springframework.integration.endpoint.PollingConsumer.handleMessage(PollingConsumer.java:74)
at org.springframework.integration.endpoint.AbstractPollingEndpoint.doPoll(AbstractPollingEndpoint.java:219)
at org.springframework.integration.endpoint.AbstractPollingEndpoint.access$000(AbstractPollingEndpoint.java:55)
at org.springframework.integration.endpoint.AbstractPollingEndpoint$1.call(AbstractPollingEndpoint.java:149)
at org.springframework.integration.endpoint.AbstractPollingEndpoint$1.call(AbstractPollingEndpoint.java:146)
at org.springframework.integration.endpoint.AbstractPollingEndpoint$Poller$1.run(AbstractPollingEndpoint.java:298)
at org.springframework.integration.util.ErrorHandlingTaskExecutor$1.run(ErrorHandlingTaskExecutor.java:52)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.kafka.common.errors.SerializationException: Can't convert value of class [B to class org.apache.kafka.common.serialization.StringSerializer specified in value.serializer
My configuration XML looks as follows:
<task:executor id="schedule-request-task-executor" pool-size="5" keep-alive="120" queue-capacity="125"/>
<bean id="kafkaStringSerializer" class="org.apache.kafka.common.serialization.StringSerializer"/>
<int-kafka:producer-context id="schedule-request-producer-context">
<int-kafka:producer-configurations>
<int-kafka:producer-configuration topic="schedule.requests"
key-serializer="kafkaStringSerializer"
value-serializer="kafkaStringSerializer"
broker-list="${kafka.brokers}"/>
</int-kafka:producer-configurations>
</int-kafka:producer-context>
<int-kafka:outbound-channel-adapter
kafka-producer-context-ref="schedule-request-producer-context"
channel="schedule-request-channel">
<int:poller receive-timeout="0"
fixed-delay="100" time-unit="MILLISECONDS"
task-executor="schedule-request-task-executor"/>
</int-kafka:outbound-channel-adapter>
And I'm sending the message with the following code:
Message message = MessageBuilder.withPayload("PAYLOAD")
.setHeader("messageKey", "KEY")
.setHeader("topic", "schedule.requests")
.build();
scheduleRequestChannel.send(message);
I looked at the samples at https://github.com/spring-projects/spring-integration-extensions/blob/master/samples/ but these seem to be outdated.

Answer 1

After debugging SI and Kafka classes, I found that this happens because Spring Integration converts the String to a byte[] unless the key-class-type and value-class-type is specified in Producer Configuration.
Here's the updated configuration in case someone is interested.
<int-kafka:producer-context id="schedule-request-producer-context">
<int-kafka:producer-configurations>
<int-kafka:producer-configuration topic="schedule.requests"
key-class-type="java.lang.String"
key-serializer="kafkaStringSerializer"
value-class-type="java.lang.String"
value-serializer="kafkaStringSerializer"
broker-list="${kafka.brokers}"/>