kafka Producer上的“ ClassCastException：kafka.message.Message无法转换为java.lang.String”

Question

I'm trying to write some simple producer to that writes messages to kafka I've downloaded kafka0.7

Run the kafka server, producer and consumer

>   bin/kafka-server-start.sh config/server.properties
>   bin/kafka-console-consumer.sh --zookeeper zooserver:2181 --topic test --from-beginning
>   bin/kafka-console-producer.sh --zookeeper zooserver:2181 --topic test

And everything working!

Then I've created simple consumer , and it is worked also.

SimpleConsumer consumer = new SimpleConsumer("172.21.110.134", 9092, 10000, 1024000);
…
ByteBufferMessageSet messages = consumer.fetch(fetchRequest);
System.out.println("consumed: " + Utils.toString(msg.message().payload(), "UTF-8"));

But the following producer always throws an error

ProducerConfig config = new ProducerConfig(props);
…
Producer<String, Message> producer = new Producer<String, Message>(config);
producer.send(new ProducerData<String, Message>("test", new Message("Hello World".getBytes())));

Getting the following exception

Exception in thread "main" java.lang.ClassCastException: kafka.message.Message cannot be cast to java.lang.String
            at kafka.serializer.StringEncoder.toMessage(Encoder.scala:30)
            at kafka.producer.ProducerPool$$anonfun$send$1$$anonfun$3$$anonfun$apply$1.apply(ProducerPool.scala:107)

I'm using in java code the maven dependencies

<dependency>
      <groupId>com.twitter</groupId>
         <artifactId>kafka_2.9.2</artifactId>
         <version>0.7.0</version>
     </dependency>

    <dependency>
         <groupId>org.scala-lang</groupId>
         <artifactId>scala-library</artifactId>
         <version>2.9.2</version>
     </dependency>

Please help, what Am I doing wrong? Why Can't I write via simple java code?

Answer 1

The problem is that you have configured wrong serializer, this should be

props.put("serializer.class", "kafka.serializer.DefaultEncoder");

Not "StringEncoder"