Messaging Pattern: Request-Reply

Messaging Pattern: Request-Reply

Request-Reply has two participants:

1. Consumer – Sends a request message and waits for a reply message.
2. Provider – Receives the request message and responds with a reply message

Example: SOAP 1.1 Messages

SOAP messages come in Request-Reply pairs. A SOAP request message indicates a service the

sender wishes to invoke on the receiver, whereas a SOAP response message contains the result of

the service invocation. The response message either contains a result value or a fault–the SOAP

equivalent of an exception.

Example: SOAP 1.2 Response Message Exchange Pattern

SOAP 1.2 introduces an explicit Request-Response Message Exchange Pattern. This patterns

describes a separate, potentially asynchronous response to a SOAP request.

Example: JMS Requestor Objects

JMS also provides QueueRequestor, a simple class for sending requests and receiving replies. A

requestor contains a QueueSender for sending requests and a QueueReceiver for receiving replies.

Each requestor creates its own temporary queue for receiving replies and specifies that in the

request's reply-to property. A requestor makes sending a request and receiving a reply very simple:

Queue Sender

        // get the initial context
    |   InitialContext ctx = new InitialContext();
    |                                                                      
    |   // lookup the queue object
    |   Queue queue = (Queue) ctx.lookup("queue/queue0");
    |                                                                      
    |   // lookup the queue connection factory
    |   QueueConnectionFactory connFactory = (QueueConnectionFactory) ctx.
    |       lookup("queue/connectionFactory");
    |                                                                      
    |   // create a queue connection
    |   QueueConnection queueConn = connFactory.createQueueConnection();
    |                                                                      
    |   // create a queue session
    |   QueueSession queueSession = queueConn.createQueueSession(false,
    |       Session.DUPS_OK_ACKNOWLEDGE);
    |                                                                      
    |   // create a queue sender
    |   QueueSender queueSender = queueSession.createSender(queue);
    |   queueSender.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
    |                                                                      
    |   // create a simple message to say "Hello"
    |   TextMessage message = queueSession.createTextMessage("Hello");
    |                                                                      
    |   // send the message
    |   queueSender.send(message);
    |                                                                      
    |   // print what we did
    |   System.out.println("sent: " + message.getText());
    |                                                                      
    |   // close the queue connection
    |   queueConn.close();

Queue Receiver

        // get the initial context
    |   InitialContext ctx = new InitialContext();
    |                                                                      
    |   // lookup the queue object
    |   Queue queue = (Queue) ctx.lookup("queue/queue0");
    |                                                                      
    |   // lookup the queue connection factory
    |   QueueConnectionFactory connFactory = (QueueConnectionFactory) ctx.
    |       lookup("queue/connectionFactory");
    |                                                                      
    |   // create a queue connection
    |   QueueConnection queueConn = connFactory.createQueueConnection();
    |                                                                      
    |   // create a queue session
    |   QueueSession queueSession = queueConn.createQueueSession(false,
    |       Session.AUTO_ACKNOWLEDGE);
    |                                                                      
    |   // create a queue receiver
    |   QueueReceiver queueReceiver = queueSession.createReceiver(queue);
    |                                                                      
    |   // start the connection
    |   queueConn.start();
    |                                                                      
    |   // receive a message
    |   TextMessage message = (TextMessage) queueReceiver.receive();
    |                                                                      
    |   // print the message
    |   System.out.println("received: " + message.getText());
    |                                                                      
    |   // close the queue connection
    |   queueConn.close();