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;

subscribeSyncWithLeaseExample(projectId, subscriptionId, numOfMessages);

}

public static void subscribeSyncWithLeaseExample(

String projectId, String subscriptionId, Integer numOfMessages)

throws IOException, InterruptedException {

SubscriberStubSettings subscriberStubSettings =

SubscriberStubSettings.newBuilder()

.setTransportChannelProvider(

SubscriberStubSettings.defaultGrpcTransportProviderBuilder()

.setMaxInboundMessageSize(20 << 20) // 20 MB

.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()) {

ackIds.add(message.getAckId());

// Modify the ack deadline of each received message from the default 10 seconds to 30.

// This prevents the server from redelivering the message after the default 10 seconds

// have passed.

ModifyAckDeadlineRequest modifyAckDeadlineRequest =

ModifyAckDeadlineRequest.newBuilder()

.setSubscription(subscriptionName)

.addAckIds(message.getAckId())

.setAckDeadlineSeconds(30)

.build();

subscriber.modifyAckDeadlineCallable().call(modifyAckDeadlineRequest);

}

// 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());

}

}