public static void main(String... args) throws Exception {

// TODO(developer): Replace these variables before running the sample.

String projectId = "your-project-id";

String subscriptionId = "your-subscription-id";

Integer numOfMessages = 10;

subscribeSyncExample(projectId, subscriptionId, numOfMessages);

}

public static void subscribeSyncExample(

String projectId, String subscriptionId, Integer numOfMessages) throws IOException {

SubscriberStubSettings subscriberStubSettings =

SubscriberStubSettings.newBuilder()

.setTransportChannelProvider(

SubscriberStubSettings.defaultGrpcTransportProviderBuilder()

.setMaxInboundMessageSize(20 * 1024 * 1024) // 20MB (maximum message size).

.build())

.build();

try (SubscriberStub subscriber = GrpcSubscriberStub.create(subscriberStubSettings)) {

String subscriptionName = ProjectSubscriptionName.format(projectId, subscriptionId);

PullRequest pullRequest =

PullRequest.newBuilder()

.setMaxMessages(numOfMessages)

.setSubscription(subscriptionName)

.build();

// Use pullCallable().futureCall to asynchronously perform this operation.

PullResponse pullResponse = subscriber.pullCallable().call(pullRequest);

// Stop the program if the pull response is empty to avoid acknowledging

// an empty list of ack IDs.

if (pullResponse.getReceivedMessagesList().isEmpty()) {

System.out.println("No message was pulled. Exiting.");

return;

}

List<String> ackIds = new ArrayList<>();

for (ReceivedMessage message : pullResponse.getReceivedMessagesList()) {

// Handle received message

// ...

ackIds.add(message.getAckId());

}

// Acknowledge received messages.

AcknowledgeRequest acknowledgeRequest =

AcknowledgeRequest.newBuilder()

.setSubscription(subscriptionName)

.addAllAckIds(ackIds)

.build();

// Use acknowledgeCallable().futureCall to asynchronously perform this operation.

subscriber.acknowledgeCallable().call(acknowledgeRequest);

System.out.println(pullResponse.getReceivedMessagesList());

}

}