Add isConsumerBatchEnabled() to listener container

In preparation for spring-projects/spring-integration#3172

Allow the inbound endpoint to detect if its listener container is configured
to return batches.

Author: garyrussell

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/MessageListenerContainer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,4 +47,14 @@ default void lazyLoad() {
 		// no-op
 	}
 
+	/**
+	 * Return true if this container is capable of (and configured to) create batches
+	 * of consumed messages.
+	 * @return true if enabled.
+	 * @since 2.2.4
+	 */
+	default boolean isConsumerBatchEnabled() {
+		return false;
+	}
+
 }

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/SimpleMessageListenerContainer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -378,6 +378,11 @@ public void setConsumerBatchEnabled(boolean consumerBatchEnabled) {
 		this.consumerBatchEnabled = consumerBatchEnabled;
 	}
 
+	@Override
+	public boolean isConsumerBatchEnabled() {
+		return this.consumerBatchEnabled;
+	}
+
 	/**
 	 * {@inheritDoc}
 	 * <p>

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/listener/MessageListenerContainerRetryIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -112,6 +112,7 @@ private void doTestRetryWithBatchListener(boolean stateful) throws Exception {
 		});
 		container.setAcknowledgeMode(AcknowledgeMode.AUTO);
 		container.setConsumerBatchEnabled(true);
+		assertThat(container.isConsumerBatchEnabled()).isTrue();
 		container.setBatchSize(2);
 
 		final CountDownLatch latch = new CountDownLatch(1);