Google Cloud Java Client for Pub/Sub
====================================

Java idiomatic client for [Google Cloud Pub/Sub][cloud-pubsub].

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- [Product Documentation][pubsub-product-docs]
- [Client Library Documentation][pubsub-client-lib-docs]

Quickstart
----------

[//]: # ({x-version-update-start:google-cloud-pubsub:released})
Add this to your pom.xml file
```xml
<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-pubsub</artifactId>
  <version>1.42.0</version>
</dependency>
```
If you are using Gradle, add this to your dependencies
```Groovy
compile 'com.google.cloud:google-cloud-pubsub:1.42.0'
```
If you are using SBT, add this to your dependencies
```Scala
libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.42.0"
```
[//]: # ({x-version-update-end})

Authentication
--------------

See the [Authentication](https://github.com/GoogleCloudPlatform/google-cloud-java#authentication) section in the base directory's README.

About Google Cloud Pub/Sub
--------------------------

[Google Cloud Pub/Sub][cloud-pubsub] 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][cloud-pubsub-quickstart] for more details on how to activate
Cloud Pub/Sub for your project.

See the [Pub/Sub client library docs][pubsub-client-lib-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](https://console.developers.google.com/) project with the Pub/Sub API
enabled. You will need to [enable billing](https://support.google.com/cloud/answer/6158867?hl=en) to
use Google Cloud Pub/Sub.
[Follow these instructions](https://cloud.google.com/docs/authentication#preparation) to get your
project set up. You will also need to set up the local development environment by [installing the
Google Cloud SDK](https://cloud.google.com/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](#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](https://developers.google.com/identity/protocols/application-default-credentials).
These credentials are automatically inferred from your environment.

For other authentication options, see the
[Authentication](https://github.com/GoogleCloudPlatform/google-cloud-java#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:

```java
import com.google.cloud.pubsub.v1.TopicAdminClient;
import com.google.pubsub.v1.ProjectTopicName;
```
Then, to create the topic, use the following code:

```java
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:

```java
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:

```java
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);
} 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:

```java
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:

```java
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:

```java
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:

```java
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](../../google-cloud-examples/src/main/java/com/google/cloud/examples/pubsub/snippets/CreateTopicAndPublishMessages.java) and [CreateSubscriptionAndConsumeMessages.java](../../google-cloud-examples/src/main/java/com/google/cloud/examples/pubsub/snippets/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](http://semver.org/).

It is currently in major version one (``1.y.z``), which means that the public API should be considered stable.

Contributing
------------

Contributions to this library are always welcome and highly encouraged.

See `google-cloud`'s [CONTRIBUTING] documentation and the [shared documentation](https://github.com/GoogleCloudPlatform/gcloud-common/blob/master/contributing/readme.md#how-to-contribute-to-gcloud) 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][code-of-conduct] for more information.

License
-------

Apache 2.0 - See [LICENSE] for more information.


[CONTRIBUTING]:https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/CONTRIBUTING.md
[code-of-conduct]:https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/CODE_OF_CONDUCT.md#contributor-code-of-conduct
[LICENSE]: https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/LICENSE
[TESTING]: https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/TESTING.md#testing-code-that-uses-pubsub

[cloud-pubsub]: https://cloud.google.com/pubsub/
[cloud-pubsub-quickstart]: https://cloud.google.com/pubsub/quickstart-console#before-you-begin
[pubsub-product-docs]: https://cloud.google.com/pubsub/docs/
[pubsub-client-lib-docs]: https://googlecloudplatform.github.io/google-cloud-java/google-cloud-clients/apidocs/index.html?com/google/cloud/pubsub/v1/package-summary.html
