Spring Cloud GCP Background Function Example

Demonstrate updating user's status through GCP Background Function

Dependencies:

• JDK 11 or later
• Project Lombok
• Spring Cloud Function GCP Adapter
• Spring Data MongoDB
• MongoDB TestContainers
• LocalServerTestSupport.java from Spring Cloud Function samples

Full dependencies can be found in pom.xml

Implementations

Test Implementation

We will start by implementing test which will verify that User's status will be updated. Our test will be based on the following scenario:

Given user status is ACTIVE
When a message is published with user status DORMANT
Then user status in database should be DORMANT

This is demonstrated in the following implementation:

class UpdateUserStatusApplicationTests {

    @Test
    @DisplayName("User status will be updated based on provided value in message")
    void contextLoads() throws IOException, InterruptedException {
        var restTemplate = new TestRestTemplate();
        var message = messageWithNewUserStatus();

        try(var process = startServer(UpdateUserStatusApplication.class, MONGO_DB_CONTAINER)) {
            restTemplate.postForObject("http://localhost:8080/", message, String.class);
        }

        var updatedUser = findById(user.getId());

        assertThat(updatedUser.getStatus()).isEqualTo(DORMANT);
    }
    
    private User findById(ObjectId id) {
        return template.findById(id, User.class);
    }

    private PubSubMessage messageWithNewUserStatus() {
        var message = new PubSubMessage();

        message.setAttributes(Map.of(
                "id", user.getId().toString(),
                "status", DORMANT.name()
        ));

        return message;
    }

}

Full implementation can be found in UpdateUserStatusApplicationTests.

Repository Implementation

UserRepository will be responsible to update User based on provided UserStatus

@Repository
@AllArgsConstructor
public class UserRepository {

    private final MongoTemplate template;

    public void updateStatusById(ObjectId id, UserStatus newStatus) {
        template.updateFirst(
                query(where("_id").is(id)),
                update("status", newStatus),
                User.class
        );
    }

}

Function Implementation

Next, we will implement a Background Function that will be triggered through PubSubMessage. PubSubMessage is a class that contains the structure of GCP Pubsub Message structure.

@Component
@AllArgsConstructor
public class UpdateUserStatusFunction implements Consumer<PubSubMessage> {

    private final UserRepository repository;

    @Override
    public void accept(PubSubMessage message) {
        var attributes = message.getAttributes();

        var id = new ObjectId(attributes.get("id"));
        var newStatus = UserStatus.valueOf(attributes.get("status"));

        repository.updateStatusById(id, newStatus);
    }

}

Define Configuration Main Class

Finally, we will need to specify our configuration main class. This is defined in MANIFEST.MF

Main-Class: scratches.boot.cloud.user.UpdateUserStatusApplication

Verify

Once all are implemented, we will verify that our implementation works by executing UpdateUserStatusApplicationTests.contextLoads. If all implementation is correct, our verification that asserts UserStatus is now DORMANT will pass.

class UpdateUserStatusApplicationTests {

    @Test
    @DisplayName("User status will be updated based on provided value in message")
    void contextLoads() throws IOException, InterruptedException {
        var updatedUser = findById(user.getId());

        assertThat(updatedUser.getStatus()).isEqualTo(DORMANT);
    }

}

Running the Function Locally

We can also run the function locally through the following command:

mvn function:run

You can find more information at Spring Cloud Function - Google Cloud Functions