samples: check for no messages case to avoid error out

Author: anguillanneuf

samples/snippets/src/main/java/pubsub/SubscribeSyncExample.java

@@ -36,6 +36,9 @@ public static void main(String... args) throws Exception {
  String projectId = "your-project-id";
  String subscriptionId = "your-subscription-id";
  Integer numOfMessages = 10;
+ projectId = "tz-playground-bigdata";
+ subscriptionId = "sub-two";
+ numOfMessages = 10;
 
  subscribeSyncExample(projectId, subscriptionId, numOfMessages);
  }
@@ -66,16 +69,21 @@ public static void subscribeSyncExample(
  // ...
  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());
+ if (ackIds.isEmpty()) {
+ System.out.println("No message was pulled.");
+ } else {
+ // 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());
+ }
  }
  }
 }