title: Receiving Kafka Key in spring boot kafka listener
body: <p>I am new in Spring Kafka. I have an microservice which sends message with a kafka key which is an user defined object. </p>
  
  <p>1) First microservice sends message to Kafka with a key which is instance of MyKey object.</p>
  
  <p>2) What I need to do is, to listen that topic and get this message with the key, and create a new key by using that Key.</p>
  
  <p>Lets say that the message is send by the key which is myKey. And what I want to do in the listener is to create a new extended key as:</p>
  
  <pre><code>     @KafkaListener(groupId = Bindings.CONSUMER_GROUP_DATA_CLEANUP, topics = "users")
       public void process( @Payload MyMessage myMessage){
  
          MyExtended myExtendedKey= new MyExtendedKey(myKey.getX(), myKey.getY());
          ....
          ....
          kafkaTemplate.send(TOPIC,  myExtendedKey, message);
        }
  </code></pre>
  
  <p>I do not know how can I get the key of the message which is sent in the listener. </p>