Update PublisherExample.java (#1097)

* Update PublisherExample.java

Author: chenyumic

pubsub/cloud-client/src/main/java/com/example/pubsub/PublisherExample.java

@@ -18,15 +18,17 @@
 // [START pubsub_quickstart_publisher]
 
 import com.google.api.core.ApiFuture;
-import com.google.api.core.ApiFutureCallback;
 import com.google.api.core.ApiFutures;
-import com.google.api.gax.rpc.ApiException;
 import com.google.cloud.ServiceOptions;
 import com.google.cloud.pubsub.v1.Publisher;
 import com.google.protobuf.ByteString;
 import com.google.pubsub.v1.ProjectTopicName;
 import com.google.pubsub.v1.PubsubMessage;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
 public class PublisherExample {
 
   // use the default project id
@@ -41,6 +43,8 @@ public static void main(String... args) throws Exception {
     int messageCount = Integer.parseInt(args[1]);
     ProjectTopicName topicName = ProjectTopicName.of(PROJECT_ID, topicId);
     Publisher publisher = null;
+    List<ApiFuture<String>> futures = new ArrayList<>();
+
     try {
       // Create a publisher instance with default settings bound to the topic
       publisher = Publisher.newBuilder(topicName).build();
@@ -54,31 +58,18 @@ public static void main(String... args) throws Exception {
             .setData(data)
             .build();
 
-        //schedule a message to be published, messages are automatically batched
+        // Schedule a message to be published. Messages are automatically batched.
         ApiFuture<String> future = publisher.publish(pubsubMessage);
-
-        // add an asynchronous callback to handle success / failure
-        ApiFutures.addCallback(future, new ApiFutureCallback<String>() {
-
-          @Override
-          public void onFailure(Throwable throwable) {
-            if (throwable instanceof ApiException) {
-              ApiException apiException = ((ApiException) throwable);
-              // details on the API exception
-              System.out.println(apiException.getStatusCode().getCode());
-              System.out.println(apiException.isRetryable());
-            }
-            System.out.println("Error publishing message : " + message);
-          }
-
-          @Override
-          public void onSuccess(String messageId) {
-            // Once published, returns server-assigned message ids (unique within the topic)
-            System.out.println(messageId);
-          }
-        });
+        futures.add(future);
       }
     } finally {
+      // Wait on any pending requests
+      List<String> messageIds = ApiFutures.allAsList(futures).get();
+
+      for (String messageId : messageIds) {
+        System.out.println(messageId);
+      }
+
       if (publisher != null) {
         // When finished with the publisher, shutdown to free up resources.
         publisher.shutdown();