Add SnsTemplate#topicExists to check with given ARN exists (#1142)

Fixes #1137

docs/src/main/asciidoc/sns.adoc

@@ -85,6 +85,8 @@ public class TopicArnResolverConfiguration {
 
 ----
 
+However, when using the topic ARN in your application, the `SnsTemplate` provides a `topicExists` method to validate the existence of the SNS topic at application startup itself.
+
 ==== SNS Operations
 
 Because of Spring Messaging compatibility, `SnsTemplate` exposes many methods that you may not need if you don't need Spring Messaging abstractions.
@@ -235,6 +237,7 @@ Following IAM permissions are required by Spring Cloud AWS:
 | To publish notification you will also need | `sns:ListTopics`
 | To use Annotation-driven HTTP notification endpoint | `sns:ConfirmSubscription`
 | For resolving topic name to ARN | `sns:CreateTopic`
+| For validating topic existence by ARN | `sns:GetTopicAttributes` 
 |===
 
 Sample IAM policy granting access to SNS:
@@ -248,7 +251,8 @@ Sample IAM policy granting access to SNS:
             "Effect": "Allow",
             "Action": [
                 "sns:Publish",
-                "sns:ConfirmSubscription"
+                "sns:ConfirmSubscription",
+                "sns:GetTopicAttributes"
             ],
             "Resource": "yourArn"
         },

spring-cloud-aws-sns/src/main/java/io/awspring/cloud/sns/core/SnsOperations.java

@@ -19,6 +19,7 @@
  * High level SNS operations.
  *
  * @author Maciej Walkowiak
+ * @author Hardik Singh Behl
  * @since 3.0
  */
 public interface SnsOperations {
@@ -30,4 +31,12 @@ public interface SnsOperations {
 	 * @param notification - the notification
 	 */
 	void sendNotification(String topic, SnsNotification<?> notification);
+
+	/**
+	 * Checks if topic with given ARN exists.
+	 * 
+	 * @param topicArn - ARN of the topic
+	 * @return true if topic exists, false otherwise
+	 */
+	boolean topicExists(String topicArn);
 }

spring-cloud-aws-sns/src/main/java/io/awspring/cloud/sns/core/SnsTemplate.java

@@ -34,6 +34,7 @@
 import org.springframework.util.Assert;
 import software.amazon.awssdk.arns.Arn;
 import software.amazon.awssdk.services.sns.SnsClient;
+import software.amazon.awssdk.services.sns.model.NotFoundException;
 
 /**
  * Helper class that simplifies synchronous sending of notifications to SNS. The only mandatory fields are
@@ -42,6 +43,7 @@
  * @author Alain Sahli
  * @author Matej Nedic
  * @author Mariusz Sondecki
+ * @author Hardik Singh Behl
  * @since 1.0
  */
 public class SnsTemplate extends AbstractMessageSendingTemplate<TopicMessageChannel>
@@ -151,6 +153,17 @@ public void addChannelInterceptor(ChannelInterceptor channelInterceptor) {
 	public void sendNotification(String topic, SnsNotification<?> notification) {
 		this.convertAndSend(topic, notification.getPayload(), notification.getHeaders());
 	}
+
+	@Override
+	public boolean topicExists(String topicArn) {
+		Assert.notNull(topicArn, "topicArn must not be null");
+		try {
+			snsClient.getTopicAttributes(request -> request.topicArn(topicArn));
+		} catch (NotFoundException exception) {
+			return false;
+		}
+		return true;
+	}
 
 	private TopicMessageChannel resolveMessageChannelByTopicName(String topicName) {
 		Arn topicArn = this.topicArnResolver.resolveTopicArn(topicName);

spring-cloud-aws-sns/src/test/java/io/awspring/cloud/sns/integration/SnsTemplateIntegrationTest.java

@@ -24,6 +24,8 @@
 import io.awspring.cloud.sns.core.SnsTemplate;
 import io.awspring.cloud.sns.core.TopicNotFoundException;
 import io.awspring.cloud.sns.core.TopicsListingTopicArnResolver;
+import net.bytebuddy.utility.RandomString;
+
 import java.util.HashMap;
 import java.util.Map;
 import org.junit.jupiter.api.AfterEach;
@@ -51,6 +53,7 @@
  * Integration tests for {@link SnsTemplate}.
  *
  * @author Matej Nedic
+ * @author Hardik Singh Behl
  */
 @Testcontainers
 class SnsTemplateIntegrationTest {
@@ -203,5 +206,25 @@ private static void createTopics() {
 			}
 		}
 	}
+
+	@Test
+	void shouldReturnFalseForNonExistingTopic() {
+		String nonExistentTopicArn = String.format("arn:aws:sns:us-east-1:000000000000:%s", RandomString.make());
+
+		boolean response = snsTemplate.topicExists(nonExistentTopicArn);
+
+		assertThat(response).isFalse();
+	}
+
+	@Test
+	void shouldReturnTrueForExistingTopic() {
+		String topicName = RandomString.make();
+		snsClient.createTopic(request -> request.name(topicName));
+		String topicArn = String.format("arn:aws:sns:us-east-1:000000000000:%s", topicName);
+
+		boolean response = snsTemplate.topicExists(topicArn);
+
+		assertThat(response).isTrue();
+	}
 
 }