GCP PubSub:Creating a Configuration Class to publish message

You declare both a class-level variable named publisher and a variable inside putMessageOnGCP called publisher. You could only use the class-level variable and populate it when it is null:

@Slf4j
public class GCPMessagePublisher {

    private static final String PROJECT_ID = "myprojectId";
    Publisher publisher = null;

    public void putMessageOnGCP(String message) throws Exception
    {
        log.info("The outgoing message to GCP PUBSUB is : "+message);
        // topic id, eg. "my-topic"
        String topicId = "topic_name";
        int messageCount = 10;
        ProjectTopicName topicName = ProjectTopicName.of(PROJECT_ID, topicId);
        List<ApiFuture<String>> futures = new ArrayList<>();

        try {
            if (publisher == null) {
                GoogleCredentials credentials = GoogleCredentials.fromStream(
                        new FileInputStream("gcp credential here ........"));

                publisher = publisher.newBuilder(topicName).setCredentialsProvider(FixedCredentialsProvider.create(credentials)).build();
            }

            for (int i = 0; i < messageCount; i++) {

                // convert message to bytes
                ByteString data = ByteString.copyFromUtf8(message);
                PubsubMessage pubsubMessage = PubsubMessage.newBuilder()
                        .setData(data)
                        .build();

                // Schedule a message to be published. Messages are automatically batched.
                ApiFuture<String> future = publisher.publish(pubsubMessage);
                futures.add(future);
            }
        } catch (Exception e) {
            System.err.println("Could not publish messages: " + e);
        } finally {
            // Wait on any pending requests
            List<String> messageIds = ApiFutures.allAsList(futures).get();

            for (String messageId : messageIds) {
                System.out.println(messageId);
            }
        }
    }
}

Note that woudl not call shutdown at the end of putMessageOnGCP as that would result in the publisher not being usable. If you need to shut down the publisher at some point, you'd have to have another method that you would call at the desired shutdown time.

Finally I am posting solution which I used to Segregate the above class into two separate methods one for pure GCP Config and another just to publish messages to GCPPUB.

**Note:**I used SpringBoot to develop my app so we may see some Spring annotations

@Service
public class GCPMessagePublisher
{

   @Value("${gcp.proj.id}")
    private static String projectId;

    @Value(("${gcp.pubsub.topic.name}"))
    private static  String topicId;


    private static  Publisher publisher = null;


    public static void buildGCPConfiguration() throws Exception
    {

        ProjectTopicName topicName = ProjectTopicName.of(projectId, topicId);
        try
        {
            GoogleCredentials credentials = GoogleCredentials.fromStream(
                    new FileInputStream("gcp credential here use the file path to key.json which you downloaded from google console........"));

            publisher = publisher.newBuilder(topicName).setCredentialsProvider(FixedCredentialsProvider.create(credentials)).build();

        }catch (Exception e)
        {
            log.error("Exception Thrown while connecting gcp"+e);
        }
    }

    public void putMessageOnGCP (String message) throws Exception
    {
        log.info("Sending Message to GCP PUBSUB......"+message)
        List<ApiFuture<String>> futures = new ArrayList<>();
        if (publisher == null) {
            buildGCPConfiguration();
        }

        ByteString data = ByteString.copyFromUtf8(message);
        PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();
        // Schedule a message to be published. Messages are automatically batched.
        ApiFuture<String> future = publisher.publish(pubsubMessage);
        futures.add(future);

    }


}