Message queues like IBM MQ enable asynchronous messaging between distributed applications and services. By using Java Message Service (JMS) APIs, Java developers can easily connect their applications to IBM MQ to leverage its reliability, scalability and flexibility for messaging. In this comprehensive guide, we’ll walk through IBM MQ Java development from basic setup to building a complete application.

Message queues like IBM MQ solve these problems by enabling asynchronous messaging between applications. One service can simply send a message to a queue, which will be delivered reliably to the receiving service. The sender doesn’t have to wait for a response. This loose coupling allows the services to scale independently. Even if one service goes down, the messages remain in the queue to be processed when it comes back up.

Java developers can leverage the power of IBM MQ in their applications easily using the Java Message Service (JMS) APIs. JMS provides a common interface to connect to any enterprise messaging system like IBM MQ and send/receive messages using similar constructs.

In this comprehensive guide, we will go through the entire process of building Java applications with IBM MQ from the ground up:

• Connecting to IBM MQ queue manager from Java
• Sending and receiving messages using JMS APIs
• Building robust and scalable applications with advanced queueing features
• Monitoring, troubleshooting and performance optimizations

By the end of this guide, you will be able to confidently develop Java applications that can reliably send and receive high volumes of messages using IBM MQ. Let’s get started!

Connecting to IBM MQ

The first step in building JMS applications with IBM MQ is setting up the connectivity between the Java code and the MQ queue manager. This involves installing the required prerequisites, creating MQ objects like queues, and writing Java code to connect to the queue manager.

Setting up the environment

The prerequisites for developing IBM MQ applications in Java are:

• JDK: Java SE 8 or higher is required to compile and run the JMS code. Oracle JDK or OpenJDK can be used.
• IBM MQ client: Install IBM MQ client libraries (e.g. com.ibm.mq.allclient) to connect to the queue manager from Java code.
• IBM MQ server: Install and configure a queue manager for message queuing. This can be on-premises or cloud-hosted like IBM MQ on IBM Cloud.

Once the prerequisites are installed, the typical steps for setting up development environment are:

1. Create a Java project and import JMS libraries like javax.jms-api.jar.
2. Add IBM MQ client jar to project build path or classpath.
3. Create MQ connection factory and queue objects by running MQSC commands like: DEFINE QCF(MY.CONN.FACTORY) + CCSID(1208) + CHANNEL(DEV.ADMIN.SVRCONN) + TRAN(CLIENT) + CONNAME('localhost(1414)') DEFINE QLOCAL(MY.QUEUE)
4. Configure security by allowing APPID access to queues and connection channels.

This sets up the basic environment to connect MQ with Java code.

Writing Java code

The typical steps for connecting to IBM MQ from Java are:

• Create a MQQueueConnectionFactory object using the connection factory configured above:

MQQueueConnectionFactory cf = new MQQueueConnectionFactory();
cf.setQueueManager(qmName);
cf.setTransportType(JMSC.MQJMS_TP_CLIENT_MQ_TCPIP);
cf.setConnectionNameList("localhost(1414)"); 

• Create a MQQueueConnection using the connection factory

MQQueueConnection connection = cf.createQueueConnection(userId, password);

• Start the connection:

connection.start();

• Create a MQQueueSession and JMS message producer/consumer

: MQQueueSession session = connection.createQueueSession(false, Session.AUTO_ACKNOWLEDGE); MQQueue sender = session.createSender(queue); MQQueueReceiver receiver = session.createReceiver(queue);

• Send messages using MQQueueSender.send() and receive them with MQQueueReceiver.receive().
• Close connections and resources after use.

This Java code establishes connectivity to the IBM MQ queue manager, which can then be used to send and receive messages programmatically.

Running and testing the application

Once the Java code is ready, compile and run it to test the end-to-end messaging functionality:

• Compile the JMS code along with MQ libraries to resolve any errors:

javac -cp mq-client-jms.jar:javax.jms-api.jar MQApp.java

• Run the application using the runjms or runmqlsr helper scripts:

runmqlsr -m MQApp -j mq-client-jms.jar:javax.jms.jar

• Verify messages sent from producer are received at the consumer end.
• Check for any runtime errors and debug as needed by enabling logging.
• Analyze MQ error logs for issues.

With this, you should be able to connect an IBM MQ queue manager from your Java application code!

Sending and Receiving Messages

Once connected to IBM MQ, JMS APIs can be used to send and receive messages in a standardized way. Let’s go through the options for sending and consuming messages from queues.

Sending messages to queues

JMS provides the following options to send messages to a queue destination:

• TextMessage – Send text content as string
• MapMessage – Send messages as name-value pairs
• BytesMessage – Send binary content as bytes
• ObjectMessage – Send Java serializable objects
• StreamMessage – Send streamed binary data

Here is an example of sending a TextMessage:

TextMessage msg = session.createTextMessage("Hello MQ!");
msg.setJMSDeliveryMode(DeliveryMode.PERSISTENT);
producer.send(msg); 

Some ways to control message delivery:

• Set priority from 0 (lowest) to 9 (highest)
• Set time-to-live in milliseconds
• Set delivery delay to control when message is delivered
• Send messages transactionally for atomicity

Receiving messages from queues

JMS provides synchronous and asynchronous ways to receive messages from queues:

Synchronous message consumption

// Receive message synchronously 
Message msg = consumer.receive();

if(msg instanceof TextMessage) {
  // Process text message
}

Asynchronous message listeners

// Asynchronous message listener
consumer.setMessageListener(new MessageListener() {
  public void onMessage(Message msg) {
    // Process message 
  }  
});

Message-driven beans

// Message-driven bean consumption
@MessageDriven(activationConfig = {
        @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue")
})
public class MessageBean implements MessageListener {

  @Override
  public void onMessage(Message msg) {
    // Process message
  }

}

The asynchronous options are useful for high-throughput messaging as they provide parallel processing.

Browsing queues and messages

Sometimes it’s useful to peek into queues or messages before consuming them:

• Queue browsing – Fetch messages without removing them from queue QueueBrowser browser = session.createBrowser(queue); Enumeration msgs = browser.getEnumeration();
• Message peek – Look at message content before consuming java Message msg = consumer.receive(peekTimeout); if(msg != null) { // Peek at content msg.peek(); }

This helps build smarter message processing logic in applications.

Building Robust Applications

There are several best practices to ensure IBM MQ based applications are robust, scalable and highly available:

Ensuring reliability

• Set appropriate message persistence to prevent message loss.
• Handle poison messages gracefully – move to dead letter queue after N retry attempts.
• Send messages transactionally to ensure atomicity.
• Configure automatic reconnection to MQ after failures.

Scaling seamlessly

• Load balance across multiple queues and queue managers.
• Use message selectors to filter messages.
• Batch messages using transactions to improve throughput.
• Horizontally scale consumers to divide load.

Monitoring and troubleshooting

• Enable MQ tracing and logging to debug issues.
• Analyze queue depth and message throughput metrics.
• Perform end-to-end tracking of messages.
• Monitor application health using heartbeats.

Properly leveraging these capabilities ensures that applications built with IBM MQ and JMS are robust, efficient and highly available.

Conclusion

IBM MQ is a powerful messaging middleware that enables building scalable and resilient distributed systems. By providing asynchronous and decoupled messaging, it makes it easy to connect disparate applications and services.

Java developers can use the standardized JMS APIs to connect to IBM MQ from their code. This guide covered the end-to-end steps – from setup and connectivity to building robust applications using IBM MQ for messaging.