How to get container registry pubsub notifications inside code (java or any other lang)

Question

My aim is to get notifications from google container registry in code whenever any image is updated/inserted/deleted from the registry.

I am following tutorial - https://cloud.google.com/container-registry/docs/configuring-notifications

I am able to pull notification messages from the registry using the google console using command - gcloud alpha pubsub subscriptions pull SUBSCRIPTION

But I want these notification messages to be delivered in code (in java).

If someone can give me any reference to any article or tutorial that will help.

After comment from dsesto i have added following code. This code gave me some messages when i run first. But after that i kept application running and tried to delete/insert images from container registry but it did not gave any message. Any suggestions.

package com.avaya.ipoffice.mcm.googleconnect;

import org.springframework.stereotype.Service;

import com.google.cloud.pubsub.v1.AckReplyConsumer;
import com.google.cloud.pubsub.v1.MessageReceiver;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PubsubMessage;

@Service
public class RecieveMessagesUtil {      
    public static void main(String... args) throws Exception {

        String projectId = "xxxxx";
        String subscriptionId = "prashantsub";

        ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(projectId, subscriptionId);
        // Instantiate an asynchronous message receiver
        MessageReceiver receiver = new MessageReceiver() {
            @Override
            public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
                // handle incoming message, then ack/nack the received message
                System.out.println("Id : " + message.getMessageId());
                System.out.println("Data : " + message.getData().toStringUtf8());
                consumer.ack();
            }
        };

        Subscriber subscriber = null;
        try {
            // Create a subscriber for "my-subscription-id" bound to the message receiver
            subscriber = Subscriber.newBuilder(subscriptionName, receiver).build();
            subscriber.startAsync();
            // ...
        } catch (Exception e) {
            System.out.println("Exception while subscribing" + e);
        } finally {
            // stop receiving messages
            if (subscriber != null) {
                subscriber.stopAsync();
            }
        }
    }
}

Answer 1

I would recommend looking at the Cloud Pub/Sub documentation, particularly, the subscriber guide, which gives you the code necessary to receive messages in Java.

Answer 2

From your question I understand that you have already successfully setup the notifications system of Container Registry using Pub/Sub topics and subscriptions, given that you said that you are already able to retrieve the messages from your Pub/Sub subscription using command gcloud pubsub subscriptions pull. Therefore, it looks like your concern is mostly related to pulling messages from a Subscription programatically.

First of all, I would recommend you to have a look at this documentation page about Subscribers in Pub/Sub. Especially, have a look at the Pull vs. Push comparison, where you will have a better idea of the possibilities available, and you should first decide whether to work with a Pull Subscription (such as the one you are using when calling the gcloud command, where the application initiates requests) or with a Push Subscription (where Pub/Sub initiates the requests to a subscriber application, such as an App Engine application).

Once that is clear (and assuming that you go for the Pull Subscription, which you are already using with gcloud), you can have a look at the documentation on how to perform Asynchronous Pull operations, with a Java-based example. Additionally, you can have a look at the complete subscriber example available in GitHub.

Finally, you should have a look at the Client Libraries documentation, more specifically the Pub/Sub Java reference, where you will find the complete documentation for the Pub/Sub Client Libraries used to work with Pub/Sub programatically.