GCP PubSub Spring Boot REST Service

Minimal Spring Boot REST service which publishes messages to a Google PubSub topic and fetches them

This is meant to illustrate how to bind a Spring Boot app to an instance of the Google PubSub service, create a subscription, publish and retrieve messages.

Prerequisite

Install the GCP tile into your PCF environment, per this procedure

Steps to deploy and run this

1. Edit the application.properties, if you like, but any change to pubsub.instance.name will also have to be applied to the service_instance variable in cf_push_command.sh
2. Build: mvn clean package
3. Run the script ./cf_push_command.sh, which does the following:
   • Pushes the app
   • Creates an instance of the Google PubSub service
   • Binds your app to this PubSub service instance, with "admin" rights
   • Starts the app

How to use the app

There are only a few REST methods provided:

• /topics will just return a comma separated list of topic names (TODO: JSON-ify this)
• /send takes a parameter, msg, which contains the message text to publish
• /fetch returns a message, and deletes it from the topic

Worth noting

• When I attempted to cf push this app, it would not start up. That led to some research, and it seems the issue was that the Google API was pulling in the servlet 2.5 API, which was missing a method found in the later 3.x API. The solution to that was to exclude that servlet API within the POM:

  <dependency>
    <groupId>com.google.cloud</groupId>
    <artifactId>google-cloud-pubsub</artifactId>
    <version>${google-cloud-pubsub.version}</version>
    <exclusions>
      <exclusion>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
      </exclusion>
    </exclusions>
  </dependency>

• The intent of this app is to bind to the PubSub service, via the GCP tile. The values within the resulting VCAP_SERVICES environment variable are exposed as properties in Spring, accessible like this, where that nested ${pubsub.instance.name} corresponds to the name given to the service instance created in PCF:

  @Bean
  public PubSub pubSubCloud(
    @Value("${vcap.services.${pubsub.instance.name}.credentials.PrivateKeyData}") String privateKeyData,
    @Value("${vcap.services.${pubsub.instance.name}.credentials.ProjectId}") String projectId
  ) throws Exception {

• It appears that a subsription name cannot contain hyphens. I had chosen a name with hyphens, and wasn't seeing it appear on the list of subscriptions, and I was unable to pull out messages. When I changed to one without hyphens, things worked normally (refer to pubsub.subscription.name in application.properties).