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Google Cloud Java Client for Pub/Sub

Java idiomatic client for Google Cloud Pub/Sub.

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Note: This client is a work-in-progress, and may occasionally make backwards-incompatible changes.

Quickstart

Add this to your pom.xml file

<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-pubsub</artifactId>
  <version>0.33.0-beta</version>
</dependency>

If you are using Gradle, add this to your dependencies

compile 'com.google.cloud:google-cloud-pubsub:0.33.0-beta'

If you are using SBT, add this to your dependencies

libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "0.33.0-beta"

Authentication

See the Authentication section in the base directory's README.

About Google Cloud Pub/Sub

Google Cloud Pub/Sub is designed to provide reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic and other applications can subscribe to that topic to receive the messages. By decoupling senders and receivers, Google Cloud Pub/Sub allows developers to communicate between independently written applications.

See the Google Cloud Pub/Sub docs for more details on how to activate Cloud Pub/Sub for your project.

See the Pub/Sub client library docs to learn how to interact with the Cloud Pub/Sub using this Client Library.

Getting Started

Prerequisites

For this tutorial, you will need a Google Developers Console project with the Pub/Sub API enabled. You will need to enable billing to use Google Cloud Pub/Sub. Follow these instructions to get your project set up. You will also need to set up the local development environment by installing the Google Cloud SDK and running the following commands in command line: gcloud auth login and gcloud config set project [YOUR PROJECT ID].

Installation and setup

You'll need to obtain the google-cloud-pubsub library. See the Quickstart section to add google-cloud-pubsub as a dependency in your code.

Creating an authorized service object

To make authenticated requests to Google Cloud Pub/Sub, you must create a service object with credentials. You can then make API calls by calling methods on the Pub/Sub service object. The simplest way to authenticate is to use Application Default Credentials. These credentials are automatically inferred from your environment.

For other authentication options, see the Authentication page.

Creating a topic

With Pub/Sub you can create topics. A topic is a named resource to which messages are sent by publishers. Add the following imports at the top of your file:

import com.google.cloud.pubsub.v1.TopicAdminClient;
import com.google.pubsub.v1.TopicName;

Then, to create the topic, use the following code:

TopicName topic = TopicName.create("test-project", "test-topic");
try (TopicAdminClient topicAdminClient = TopicAdminClient.create()) {
  topicAdminClient.createTopic(topic);
}

Publishing messages

With Pub/Sub you can publish messages to a topic. Add the following import at the top of your file:

import com.google.api.core.ApiFuture;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.PubsubMessage;

Then, to publish messages asynchronously, use the following code:

Publisher publisher = null;
try {
  publisher = Publisher.defaultBuilder(topic).build();
  ByteString data = ByteString.copyFromUtf8("my-message");
  PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();
  ApiFuture<String> messageIdFuture = publisher.publish(pubsubMessage);
} finally {
  if (publisher != null) {
    publisher.shutdown();
  }
}

Creating a subscription

With Pub/Sub you can create subscriptions. A subscription represents the stream of messages from a single, specific topic. Add the following imports at the top of your file:

import com.google.cloud.pubsub.v1.SubscriptionAdminClient;
import com.google.pubsub.v1.PushConfig;
import com.google.pubsub.v1.SubscriptionName;
import com.google.pubsub.v1.TopicName;

Then, to create the subscription, use the following code:

TopicName topic = TopicName.create("test-project", "test-topic");
SubscriptionName subscription = SubscriptionName.create("test-project", "test-subscription");

try (SubscriptionAdminClient subscriptionAdminClient = SubscriptionAdminClient.create()) {
  subscriptionAdminClient.createSubscription(subscription, topic, PushConfig.getDefaultInstance(), 0);
}

Pulling messages

With Pub/Sub you can pull messages from a subscription. Add the following imports at the top of your file:

import com.google.cloud.pubsub.v1.AckReplyConsumer;
import com.google.cloud.pubsub.v1.MessageReceiver;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.SubscriptionName;
import com.google.pubsub.v1.TopicName;

Then, to pull messages asynchronously, use the following code:

MessageReceiver receiver =
    new MessageReceiver() {
      @Override
      public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
        System.out.println("got message: " + message.getData().toStringUtf8());
        consumer.ack();
      }
    };
Subscriber subscriber = null;
try {
  subscriber = Subscriber.defaultBuilder(subscriptionName, receiver).build();
  subscriber.addListener(
      new Subscriber.Listener() {
        @Override
        public void failed(Subscriber.State from, Throwable failure) {
          // Handle failure. This is called when the Subscriber encountered a fatal error and is shutting down.
          System.err.println(failure);
        }
      },
      MoreExecutors.directExecutor());
  subscriber.startAsync().awaitRunning();
  //...
} finally {
  if (subscriber != null) {
    subscriber.stopAsync();
  }
}

Complete source code

In CreateTopicAndPublishMessages.java and CreateSubscriptionAndConsumeMessages.java we put together all the code shown above into two programs. The programs assume that you are running on Compute Engine, App Engine Flexible or from your own desktop.

Transport

Pub/Sub uses gRPC for the transport layer.

Java Versions

Java 7 or above is required for using this client.

Testing

This library has tools to help make tests for code using Cloud Pub/Sub.

See TESTING to read more about testing.

Versioning

This library follows Semantic Versioning.

It is currently in major version zero (0.y.z), which means that anything may change at any time and the public API should not be considered stable.

Contributing

Contributions to this library are always welcome and highly encouraged.

See google-cloud's CONTRIBUTING documentation and the shared documentation for more information on how to get started.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms. See Code of Conduct for more information.

License

Apache 2.0 - See LICENSE for more information.