How to Integrate Google Cloud Pub/Sub API in Java

Integrate Google Cloud Pub/Sub in Java

• Add the Pub/Sub dependency to your project. Ensure that your `pom.xml` includes the necessary dependency for Pub/Sub if you're using Maven.

<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-pubsub</artifactId>
  <version>1.116.3</version> <!-- Ensure this is the latest version -->
</dependency>

• Initialize the Pub/Sub client. Use Google's credential setup to authenticate and interact with the Pub/Sub API within your Java application.

import com.google.cloud.pubsub.v1.Publisher;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.pubsub.v1.ProjectTopicName;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PubsubMessage;
import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutures;
import com.google.api.gax.rpc.ApiException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

String projectId = "your-project-id";
String topicId = "your-topic-id";

// Create a topic name
ProjectTopicName topicName = ProjectTopicName.of(projectId, topicId);

• Publish a message. Use the `Publisher` class from the library to publish messages to your topic.

Publisher publisher = null;
try {
  // Create a publisher instance with default settings
  publisher = Publisher.newBuilder(topicName).build();

  String message = "Hello, Pub/Sub!";
  ByteString data = ByteString.copyFromUtf8(message);
  PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();

  // Schedule a message to be published
  ApiFuture<String> messageIdFuture = publisher.publish(pubsubMessage);

  // Add a callback
  ApiFutures.addCallback(messageIdFuture, new ApiFutureCallback<String>() {
    @Override
    public void onSuccess(String messageId) {
      System.out.println("Published with message ID: " + messageId);
    }

    @Override
    public void onFailure(Throwable t) {
      System.out.println("Failed to publish: " + t);
    }
  }, MoreExecutors.directExecutor());

} catch (IOException e) {
    e.printStackTrace();
} finally {
  if (publisher != null) {
    try {
      publisher.shutdown();
      publisher.awaitTermination(1, TimeUnit.MINUTES);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

• Subscribe to a topic. Implement a subscriber to process messages received in a subscription.

String subscriptionId = "your-subscription-id";

// Create a subscription name
ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(projectId, subscriptionId);

MessageReceiver receiver =
    (PubsubMessage message, AckReplyConsumer consumer) -> {
      System.out.println("Message Id: " + message.getMessageId());
      System.out.println("Data: " + message.getData().toStringUtf8());
      consumer.ack();
    };

Subscriber subscriber = null;
try {
  subscriber = Subscriber.newBuilder(subscriptionName, receiver).build();
  subscriber.startAsync().awaitRunning();

  // Allow the subscriber to run indefinitely unless an error occurs
  subscriber.awaitTerminated();
} catch (TimeoutException e) {
  subscriber.stopAsync();
}

• Handle exceptions and cleanup resources. Ensure that resources like `Publisher` and `Subscriber` are shut down gracefully to prevent resource leaks or unintended behavior.

try {
  if (publisher != null) {
    publisher.shutdown();
    publisher.awaitTermination(1, TimeUnit.MINUTES);
  }
  if (subscriber != null) {
    subscriber.stopAsync();
  }
} catch (Exception e) {
  e.printStackTrace();
}

• Test your implementation. Once you've integrated Pub/Sub into your application, perform tests to ensure messages are correctly published and received.