Java Message Service, 2nd Edition

Message Correlation

In the previous code example, the borrower sent a loan request on a request queue and waited for a reply from the lender on a response queue. Many borrowers may be making requests at the same time, meaning that the lender application is sending many messages to the response queue. Since the response queue may contain many messages, how can you be sure that the response you received from the lender was meant for you and not another borrower?

In general, whenever using the request/reply model, you must make sure the response you are receiving is associated with the original message you sent. Message correlation is the technique used to ensure that you receive the right message. The most popular method for correlating messages is leveraging the JMSCorrelationID message header property in conjunction with the JMSMessageID header property. The JMSCorrelationID property contains a unique String value that is known by both the sender and receiver. The JMSMessageID is typically used, since it is unique and is available to the sender and receiver.

When the message consumer (e.g., QLender) is ready to send the reply message, it sets the JMSCorrelationID message property to the message ID from the original message:

public class QLender implements MessageListener {

   ...
   public void onMessage(Message message) {
      try {
         ...         
         // Send the results back to the borrower
         TextMessage tmsg = qSession.createTextMessage();
         tmsg.setText(accepted ? "Accepted!" : "Declined");
         tmsg.setJMSCorrelationID(message.getJMSMessageID()); ...