The code samples demonstrate two ways to send messages to and receive messages from Cloud Pub/Sub from your Spring application using:

• Spring Integration Channel Adapters
• Spring Cloud Stream Binders

When the application starts, it will do the following every ten seconds:

1. send a message which contains a random integer [0-1000) to a Pub/Sub topic topic-one via a Spring Cloud Stream output binder;
2. the message is then received by the application via a Spring Integration inbound channel adapter configured to listen to sub-one;
3. the same message is published to a second Pub/Sub topic topic-two via a Spring Integration outbound channel adapter;
4. the message is received again by the application via a Spring Cloud Stream input binder bound to topic-two.

This sample requires Java and Maven for building the application.

1. Follow the Java development environment set-up instructions in the documentation.

2. Enable APIs for your project. Click here to visit Cloud Platform Console and enable the Google Cloud Pub/Sub API.

3. Create a new topic topic-one and attach a subscription sub-one to it, then do the same for topic-two and sub-two, via the Cloud Platform Console's Cloud Pub/Sub section.

4. Enable application default credentials by running the command gcloud auth application-default login.

5. Run the following Maven or Gradle commands to run PubSubApplication:

   mvn clean spring-boot:run

   gradle bootRun

   You should observe an incoming message getting sent to topic-one, received from sub-one, sent to topic-two, and received from topic-two in the logged messages:

   2020-08-10 17:29:18.807  INFO 27310 --- [           main] demo.PubSubApplication                   : Started PubSubApplication in 6.063 seconds (JVM running for 6.393)
   2020-08-10 17:29:27.084  INFO 27310 --- [      elastic-3] demo.PubSubApplication                   : Sending a message via the output binder to topic-one! Payload: message-548
   2020-08-10 17:29:27.604  INFO 27310 --- [sub-subscriber1] o.s.i.h.s.MessagingMethodInvokerHelper   : Overriding default instance of MessageHandlerMethodFactory with provided one.
   2020-08-10 17:29:27.608  INFO 27310 --- [sub-subscriber1] demo.PubSubApplication                   : Message arrived via an inbound channel adapter from sub-one! Payload: message-548
   2020-08-10 17:29:28.269  INFO 27310 --- [bsub-publisher1] demo.PubSubApplication                   : Message was sent via the outbound channel adapter to topic-two!
   2020-08-10 17:29:28.269  INFO 27310 --- [sub-subscriber2] o.s.i.h.s.MessagingMethodInvokerHelper   : Overriding default instance of MessageHandlerMethodFactory with provided one.
   2020-08-10 17:29:28.290  INFO 27310 --- [sub-subscriber2] demo.PubSubApplication                   : Message arrived via an input binder from topic-two! Payload: message-548