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Google Cloud Pub/Sub Client for Java

Java idiomatic client for Cloud Pub/Sub.

Maven Stability

Quickstart

If you are using Maven with BOM, add this to your pom.xml file

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>libraries-bom</artifactId>
      <version>5.1.0</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  <dependency>
    <groupId>com.google.cloud</groupId>
    <artifactId>google-cloud-pubsub</artifactId>
  </dependency>

If you are using Maven without BOM, add this to your dependencies:

<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-pubsub</artifactId>
  <version>1.105.0</version>
</dependency>

If you are using Gradle, add this to your dependencies

compile 'com.google.cloud:google-cloud-pubsub:1.106.0'

If you are using SBT, add this to your dependencies

libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.106.0"

Authentication

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

Getting Started

Prerequisites

You will need a Google Cloud Platform Console project with the Cloud 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.

About Cloud Pub/Sub

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 Cloud Pub/Sub client library docs to learn how to use this Cloud Pub/Sub Client Library.

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.ProjectTopicName;

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

ProjectTopicName topic = ProjectTopicName.of("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.api.core.ApiFutureCallback;
import com.google.api.core.ApiFutures;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.common.util.concurrent.MoreExecutors;
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.newBuilder(topic).build();
  ByteString data = ByteString.copyFromUtf8("my-message");
  PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();
  ApiFuture<String> messageIdFuture = publisher.publish(pubsubMessage);
  ApiFutures.addCallback(messageIdFuture, new ApiFutureCallback<String>() {
    public void onSuccess(String messageId) {
      System.out.println("published with message id: " + messageId);
    }

    public void onFailure(Throwable t) {
      System.out.println("failed to publish: " + t);
    }
  }, MoreExecutors.directExecutor());
  //...
} finally {
  if (publisher != null) {
    publisher.shutdown();
    publisher.awaitTermination(1, TimeUnit.MINUTES);
  }
}

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.ProjectSubscriptionName;
import com.google.pubsub.v1.ProjectTopicName;

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

ProjectTopicName topic = ProjectTopicName.of("test-project", "test-topic");
ProjectSubscriptionName subscription = ProjectSubscriptionName.of("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.ProjectSubscriptionName;
import com.google.pubsub.v1.ProjectTopicName;

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

ProjectSubscriptionName subscription = ProjectSubscriptionName.of("test-project", "test-subscription");

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.newBuilder(subscription, 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.

Troubleshooting

To get help, follow the instructions in the shared Troubleshooting document.

Java Versions

Java 7 or above is required for using this client.

Versioning

This library follows Semantic Versioning.

Contributing

Contributions to this library are always welcome and highly encouraged.

See CONTRIBUTING for more information 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.

CI Status

Java Version Status
Java 7 Kokoro CI
Java 8 Kokoro CI
Java 8 OSX Kokoro CI
Java 8 Windows Kokoro CI
Java 11 Kokoro CI