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 2.0 API over AMQP using the Solace Message Router. 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 2.0 API

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

Connecting to the Solace Messaging

In order to send or receive messages, an application must start a JMS connection and a session.

There are three parameters for establishing the JMS connection: the Solace messaging host name with the AMQP service port number, the client username and the optional password.

BasicRequestor.java/BasicReplier.java

String solaceHost = args[0];
String solaceUsername = args[1];
String solacePassword = args[2];
ConnectionFactory connectionFactory = new JmsConnectionFactory(solaceUsername, solacePassword, solaceHost);

Notice how JMS 2.0 API combines Connection and Session objects into the JMSContext object.

BasicRequestor.java/BasicReplier.java

JMSContext context = connectionFactory.createContext()

The session created by the JMSContext object by default is non-transacted and uses the acknowledge mode that automatically acknowledges a client’s receipt of a message.

Notice how JMS 2.0 API combines Connection and Session objects into the JMSContext object.

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 a JMS Producer needs to be created.

sending-message-to-queue

Also, it is necessary to allocate a temporary queue for receiving the reply.

BasicRequestor.java

TemporaryQueue replyToQueue = context.createTemporaryQueue();

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 = context.createTextMessage("Sample Request");
request.setJMSReplyTo(replyToQueue);
String correlationId = UUID.randomUUID().toString();
request.setJMSCorrelationID(correlationId);

Now we create a JMS producer and send the request. We assign the delivery mode to non-persistent for better performance.

The JMS 2.0 API allows the use of method chaining to create the producer, set the delivery mode and send the message.

BasicRequestor.java

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

Topic requestTopic = context.createTopic(REQUEST_TOPIC_NAME);
context.createProducer().setDeliveryMode(DeliveryMode.NON_PERSISTENT).send(requestTopic, request);

Receiving a request

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

We create a JMS consumer and receive the request in the same, main thread.

The JMS 2.0 API allows the use of method chaining to create the consumer and receive a message from the queue.

BasicReplier.java

Topic requestTopic = context.createTopic(REQUEST_TOPIC_NAME);
Message request = context.createConsumer(requestTopic).receive();

Replying to a request

To reply to a received request a JMS Producer needs to be created.

Request-Reply_diagram-3

The reply message must have the JMSCorrelationID property value assigned from the received request. Create the reply message using the current JMSContext and assign its JMSCorrelationID property from the request value:

BasicReplier.java

Message request = context.createConsumer(requestTopic).receive();

TextMessage reply = context.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. 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 way the Apache Qpid JMS client is implementated.

BasicReplier.java

Destination replyDestination = request.getJMSReplyTo();
String replyDestinationName = ((JmsDestination) replyDestination).getName();
replyDestination = new JmsTemporaryQueue(replyDestinationName);

A JMS producer needs to be created to send the reply message. Assign its delivery mode to non-persistent for better performance.

The JMS 2.0 API allows the use of method chaining to create the producer, set the delivery mode and send the reply message.

BasicReplier.java

context.createProducer().setDeliveryMode(DeliveryMode.NON_PERSISTENT).send(replyDestination, reply);

The reply will be received in the main thread by the BasicRequestor.

BasicRequestor.java

final int REPLY_TIMEOUT_MS = 10000;

Message reply = context.createConsumer(replyToQueue).receive(REPLY_TIMEOUT_MS);

If you execute the BasicReplier.java program, it will block at the context.createConsumer(requestTopic).receive() call until a request is received. Now, if you execute the BasicRequestor.java that sends the request, the BasicReplier.java program will resume and reply to the request. That will unblock the BasicRequestor.java program that was blocked on the context.createConsumer(replyToQueue).receive(REPLY_TIMEOUT_MS) call waiting for the reply to its request.

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-jms2
cd solace-samples-amqp-qpid-jms2

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 router amqp://<HOST:AMQP_PORT>...
Connected to the Solace router 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 router amqp://<HOST:AMQP_PORT>...
Connected to the Solace router 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@527740a2 }

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 2.0 API 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.