Implementing publish-subscribe messaging with Hazelcast in Java

21 Sep 2023

Publish-Subscribe messaging is a common pattern used in distributed systems to enable communication between multiple components. It allows publishers to send messages to a group of subscribers who are interested in receiving those messages. Hazelcast is a popular in-memory data grid that provides support for distributed pub-sub messaging. In this blog post, we will explore how to implement publish-subscribe messaging using Hazelcast in Java.

Setting up Hazelcast

First, let’s set up Hazelcast in our Java project. You can add the Hazelcast dependency to your pom.xml file if you are using Maven, or include the JAR file in your project manually. Once you have Hazelcast set up, you can proceed with implementing the pub-sub messaging.

Creating a Publisher

To implement the publisher, we need to perform the following steps:

Create a Hazelcast instance:

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;
   
HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();

Retrieve the topic to which you want to publish messages:

import com.hazelcast.core.ITopic;
   
ITopic<String> topic = hazelcastInstance.getTopic("my-topic");

Publish messages to the topic:

String message = "Hello, subscribers!";
topic.publish(message);

The publisher is now ready to send messages to the topic. Each message will be delivered to all subscribers of the topic.

Creating a Subscriber

To implement the subscriber, we need to perform the following steps:

Create a Hazelcast instance:

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;
   
HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();

Retrieve the topic to which you want to subscribe:

import com.hazelcast.core.ITopic;
   
ITopic<String> topic = hazelcastInstance.getTopic("my-topic");

Subscribe to the topic and define a callback to process the received messages:

topic.addMessageListener(message -> {
    String receivedMessage = message.getMessageObject();
    System.out.println("Received message: " + receivedMessage);
});

The subscriber is now ready to receive messages published to the topic. Each message will be processed by the defined callback method.

Conclusion

In this blog post, we explored how to implement publish-subscribe messaging using Hazelcast in Java. By following the steps mentioned, you can set up a publisher to send messages and a subscriber to receive those messages. Hazelcast provides a reliable messaging system that can be easily integrated into your distributed systems architecture.

#publishing #messaging