Request/Reply

Request/Reply

This tutorial outlines both roles in the request-response message exchange pattern. It will show you how to act as the client by creating a request, sending it and waiting for the response. It will also show you how to act as the server by receiving incoming requests, creating a reply and sending it back to the client. It builds on the basic concepts introduced in publish/subscribe tutorial.

At the end, this tutorial walks through downloading and running the sample from source.

This tutorial focuses on using a non-Solace JMS API implementation. For using the Solace JMS API see Solace Getting Started JMS Tutorials.

Assumptions

This tutorial assumes the following:

  • You are familiar with Solace core concepts.
  • You have access to Solace messaging with the following configuration details:
    • Connectivity information for a Solace message-VPN
    • Enabled client username and password

One simple way to get access to Solace messaging quickly is to create a messaging service in Solace Cloud as outlined here. You can find other ways to get access to Solace messaging below.

Goals

The goal of this tutorial is to demonstrate how to use Apache Qpid JMS 1.1 over AMQP using Solace messaging. This tutorial will show you:

  1. How to build and send a request message
  2. How to receive a request message and respond to it

Get Solace Messaging

This tutorial requires access Solace messaging and requires that you know several connectivity properties about your Solace messaging. Specifically you need to know the following:

Resource Value Description
Host String This is the address clients use when connecting to the Solace messaging to send and receive messages. (Format: DNS_NAME:Port or IP:Port)
Client Username String The client username. (See Notes below)
Client Password String The client password. (See Notes below)

There are several ways you can get access to Solace Messaging and find these required properties.

Option 1: Use Solace Cloud

  • Follow these instructions to quickly spin up a cloud-based Solace messaging service for your applications.
  • The messaging connectivity information is found in the service details in the connectivity tab (shown below). You will need:
    • Host:Port (use the AMQP URI)
    • Client Username
    • Client Password

Option 2: Start a Solace VMR

  • Follow these instructions to start the Solace VMR in leading Clouds, Container Platforms or Hypervisors. The tutorials outline where to download and how to install the Solace VMR.
  • The messaging connectivity information are the following:
    • Host: <public_ip> (IP address assigned to the VMR in tutorial instructions)
    • Client Username: sampleUser (can be any value)
    • Client Password: samplePassword (can be any value)

    Note: By default, the Solace VMR “default” message VPN has authentication disabled.

Option 3: Get access to a Solace appliance

  • Contact your Solace appliance administrators and obtain the following:
    • A Solace Message-VPN where you can produce and consume direct and persistent messages
    • The host name or IP address of the Solace appliance hosting your Message-VPN
    • A username and password to access the Solace appliance

Obtaining Apache Qpid JMS 1.1

This tutorial assumes you have downloaded and successfully installed the Apache Qpid JMS client. If your environment differs from the example, then adjust the build instructions appropriately.

The easiest way to install it is through Gradle or Maven.

Get the API: Using Gradle

dependencies {
    compile("org.apache.qpid:qpid-jms-client:0.27.0")
}

Get the API: Using Maven

<dependency>
    <groupId>org.apache.qpid</groupId>
    <artifactId>qpid-jms-client</artifactId>
    <version>0.27.0</version>
</dependency>

Java Messaging Service (JMS) Introduction

JMS is a standard API for sending and receiving messages. As such, in addition to information provided on the Solace developer portal, you may also look at some external sources for more details about JMS. The following are good places to start

  1. http://java.sun.com/products/jms/docs.html.
  2. https://en.wikipedia.org/wiki/Java_Message_Service
  3. https://docs.oracle.com/javaee/7/tutorial/partmessaging.htm#GFIRP3

The last (Oracle docs) link points you to the JEE official tutorials which provide a good introduction to JMS.

This tutorial focuses on using JMS 1.1 (April 12, 2002), for JMS 2.0 (May 21, 2013) see Solace Getting Started AMQP JMS 2.0 Tutorials.

Connecting to Solace Messaging

As in the publish/subscribe tutorial tutorial, an application must start a JMS connection and a session.

TopicPublisher.java/TopicSubscriber.java


ConnectionFactory connectionFactory = new JmsConnectionFactory(solaceUsername, solacePassword, solaceHost);
Connection connection = connectionFactory.createConnection();
Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

At this point the application is connected to Solace messaging and ready to send and receive request and reply messages.

Sending a request

In order to send a request in the Requestor a JMS MessageProducer needs to be created.

BasicRequestor.java

final String REQUEST_TOPIC_NAME = "T/GettingStarted/requests";

Topic requestTopic = session.createTopic(REQUEST_TOPIC_NAME);
MessageProducer requestProducer = session.createProducer(null);

Also, it is necessary to allocate a temporary queue for receiving the reply and to create a JMS MessageConsumer for it.

BasicRequestor.java

TemporaryQueue replyToQueue = session.createTemporaryQueue();
MessageConsumer replyConsumer = session.createConsumer(replyToQueue);

The request must have two properties assigned: JMSReplyTo and JMSCorrelationID.

The JMSReplyTo property needs to have the value of the temporary queue for receiving the reply that was already created.

The JMSCorrelationID property needs to have an unique value so the requestor to correlate the request with the subsequent reply.

The figure below outlines the exchange of messages and the role of both properties.

BasicRequestor.java

TextMessage request = session.createTextMessage("Sample Request");
String correlationId = UUID.randomUUID().toString();
request.setJMSCorrelationID(correlationId);

Now send the request:

BasicRequestor.java

requestProducer.send(requestTopic, request, DeliveryMode.NON_PERSISTENT,
        Message.DEFAULT_PRIORITY,
        Message.DEFAULT_TIME_TO_LIVE);

Receiving a request

In order to receive a request from a queue a JMS MessageConsumer needs to be created.

BasicReplier.java

final String REQUEST_TOPIC_NAME = "T/GettingStarted/requests";

Topic requestTopic = session.createTopic(REQUEST_TOPIC_NAME);
MessageConsumer requestConsumer = session.createConsumer(requestTopic);

As in the publish/subscribe tutorial, we will be using the anonymous inner class for receiving messages asynchronously.

BasicReplier.java

requestConsumer.setMessageListener(new MessageListener() {
    @Override
    public void onMessage(Message request) {
...
});

Replying to a request

To reply to a received request a JMS MessageProducer needs to be created in the Replier.

Request-Reply_diagram-3

The JMS MessageProducer is created without its target queue as it will be assigned from the JMSReplyTo property value of the received request.

BasicReplier.java

MessageProducer replyProducer = session.createProducer(null);

The reply message must have the JMSCorrelationID property value assigned from the received request.

BasicReplier.java

TextMessage reply = session.createTextMessage();
String text = "Sample response";
reply.setText(text);

reply.setJMSCorrelationID(request.getJMSCorrelationID());

Now we can send the reply message.

We must send it to the temporary queue that was created by the requestor. We need to create an instance of the org.apache.qpid.jms.JmsDestination class for the reply destination and assign it a name from the request JMSReplyTo property because of the Apache Qpid JMS implementation.

BasicReplier.java

Destination replyDestination = request.getJMSReplyTo();
String replyDestinationName = ((JmsDestination) replyDestination).getName();
replyDestination = new JmsTemporaryQueue(replyDestinationName);
replyProducer.send(replyDestination, reply, DeliveryMode.NON_PERSISTENT,
        Message.DEFAULT_PRIORITY,
        Message.DEFAULT_TIME_TO_LIVE);

The reply will be received by BasicRequestor in a main thread after the following call unblocks:

final int REPLY_TIMEOUT_MS = 10000;
Message reply = replyConsumer.receive(REPLY_TIMEOUT_MS);

Summarizing

Combining the example source code shown above results in the following source code files:

Getting the Source

Clone the GitHub repository containing the Solace samples.

git clone https://github.com/SolaceSamples/solace-samples-amqp-qpid-jms1
cd solace-samples-amqp-qpid-jms1

Building

You can build and run both example files directly from Eclipse or with Gradle.

./gradlew assemble

The examples can be run as:

cd build/staged/bin
./basicReplier amqp://<HOST:AMQP_PORT> <USERNAME> <PASSWORD>
./basicRequestor amqp://<HOST:AMQP_PORT> <USERNAME> <PASSWORD>

Sample Output

First start the BasicReplier so that it is up and waiting for requests.

$ basicReplier amqp://<HOST:AMQP_PORT> <USERNAME> <PASSWORD>
BasicReplier is connecting to Solace messaging at amqp://<HOST:AMQP_PORT>...
Connected to the Solace messaging with client username 'clientUsername'.
Awaiting request...

Then you can start the BasicRequestor to send the request and receive the reply.

$ basicRequestor amqp://<HOST:AMQP_PORT> <USERNAME> <PASSWORD>
BasicRequestor is connecting to Solace messaging at amqp://<HOST:AMQP_PORT>...
Connected to the Solace messaging with client username 'clientUsername'.
Sending request 'Sample Request' to topic 'T/GettingStarted/requests'...
Sent successfully. Waiting for reply...
TextMessage response received: 'Sample response'
Message Content:
JmsTextMessage { org.apache.qpid.jms.provider.amqp.message.AmqpJmsTextMessageFacade@64bf3bbf }

Notice how the request is received by the BasicReplier and replied to.

Awaiting request...
Received request, responding...
Responded successfully. Exiting...

Now you know how to use Apache Qpid JMS 1.1 over AMQP using Solace messaging to implement the request/reply message exchange pattern.

If you have any issues sending and receiving request or reply, check the Solace community for answers to common issues seen.