Conversations are message exchanges which are between a single client and a service. They are a fundmentally important concept in ErraiBus, since by default, a message will be broadcast to all client services listening on a particular channel.

When you create a reply with an incoming message, you ensure that the message you are sending back is received by the same client which sent the incoming message. A simple example:

@Service
public class HelloWorldService implements MessageCallback {
  public void callback(CommandMessage message) {
    // Send a message to the 'HelloWorldClient' on the client that sent us the
    // the message.
    MessageBuilder.createConversation(message)
      .toSubject("HelloWorldClient")
      .signalling()
      .with("text", "Hi There! We're having a reply!")
      .noErrorHandling().reply();
    });
  }
}

Note that the only difference between the example in the previous section and this is the use of the createConversation() method with MessageBuilder.