Fix infinite stream of results bug in auto paginator APIs when the next token is an empty string

Author: varunnvs92

.changes/next-release/bugfix-AWSSDKforJavav2-2e246bc.json

@@ -0,0 +1,5 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "type": "bugfix", 
+    "description": "Fix infinite stream of results bug in auto paginator APIs when the next token is an empty string"
+}

core/sdk-core/src/main/java/software/amazon/awssdk/core/util/PaginatorUtils.java

@@ -31,13 +31,17 @@ private PaginatorUtils() {
      *
      * @param outputToken the output token to check
      * @param <T> the type of the output token
-     * @return true if the output token is non-null or non-empty if the output token is a map or Collection type
+     * @return true if the output token is non-null or non-empty if the output token is a String or map or Collection type
      */
     public static <T> boolean isOutputTokenAvailable(T outputToken) {
         if (outputToken == null) {
             return false;
         }
 
+        if (outputToken instanceof String) {
+            return !((String) outputToken).isEmpty();
+        }
+
         if (outputToken instanceof Map) {
             return !((Map) outputToken).isEmpty();
         }

services/ec2/src/test/java/software/amazon/awssdk/services/ec2/Ec2AutoPaginatorIntegrationTest.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2010-2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.services.ec2;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.time.Instant;
+import java.util.stream.Stream;
+import org.junit.Test;
+import software.amazon.awssdk.regions.Region;
+import software.amazon.awssdk.services.ec2.model.SpotPrice;
+import software.amazon.awssdk.services.ec2.paginators.DescribeSpotPriceHistoryPublisher;
+import software.amazon.awssdk.testutils.service.AwsIntegrationTestBase;
+
+public class Ec2AutoPaginatorIntegrationTest extends AwsIntegrationTestBase {
+
+    @Test
+    public void testSpotPriceHistorySyncPaginator() {
+        Ec2Client ec2Client = Ec2Client.builder()
+                                       .region(Region.US_EAST_1)
+                                       .credentialsProvider(CREDENTIALS_PROVIDER_CHAIN)
+                                       .build();
+
+        Stream<SpotPrice> spotPrices = ec2Client.describeSpotPriceHistoryPaginator(builder -> {
+            builder.availabilityZone("us-east-1a")
+                   .productDescriptions("Linux/UNIX (Amazon VPC)")
+                   .instanceTypesWithStrings("t1.micro")
+                   .startTime(Instant.now().minusMillis(1));
+        }).spotPriceHistory().stream();
+
+        assertThat(spotPrices.count()).isEqualTo(1);
+    }
+
+    @Test
+    public void testSpotPriceHistoryAsyncPaginator() {
+        Ec2AsyncClient ec2Client = Ec2AsyncClient.builder()
+                                                 .region(Region.US_EAST_1)
+                                                 .credentialsProvider(CREDENTIALS_PROVIDER_CHAIN)
+                                                 .build();
+
+        DescribeSpotPriceHistoryPublisher publisher = ec2Client.describeSpotPriceHistoryPaginator(builder -> {
+            builder.availabilityZone("us-east-1a")
+                   .productDescriptions("Linux/UNIX (Amazon VPC)")
+                   .instanceTypesWithStrings("t1.micro")
+                   .startTime(Instant.now().minusMillis(1));
+        });
+
+        publisher.subscribe(r -> assertThat(r.spotPriceHistory().size()).isEqualTo(1))
+                 .join();
+    }
+}