Polish "Add support for Kafka batch listener"

This commit reworks the property to be an enum with the list of
supported listener types rather than a boolean that flip to a
batch listener.

Closes gh-9448

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/kafka/ConcurrentKafkaListenerContainerFactoryConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -68,7 +68,9 @@ public class ConcurrentKafkaListenerContainerFactoryConfigurer {
 		if (container.getConcurrency() != null) {
 			listenerContainerFactory.setConcurrency(container.getConcurrency());
 		}
-		listenerContainerFactory.setBatchListener(container.getBatchListener());
+		if (container.getType() == Listener.Type.BATCH) {
+			listenerContainerFactory.setBatchListener(true);
+		}
 	}
 
 }

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/kafka/KafkaProperties.java

@@ -645,6 +645,25 @@ public class KafkaProperties {
 
 	public static class Listener {
 
+		public enum Type {
+
+			/**
+			 * Invokes the endpoint with one ConsumerRecord at a time.
+			 */
+			SINGLE,
+
+			/**
+			 * Invokes the endpoint with a batch of ConsumerRecord.
+			 */
+			BATCH;
+
+		}
+
+		/**
+		 * Listener type.
+		 */
+		private Type type = Type.SINGLE;
+
 		/**
 		 * Listener AckMode; see the spring-kafka documentation.
 		 */
@@ -672,10 +691,13 @@ public class KafkaProperties {
 		 */
 		private Long ackTime;
 
-		/**
-		 * If true listener container factory will be configured to create batch listener.
-		 */
-		private boolean batchListener;
+		public Type getType() {
+			return this.type;
+		}
+
+		public void setType(Type type) {
+			this.type = type;
+		}
 
 		public AckMode getAckMode() {
 			return this.ackMode;
@@ -717,13 +739,6 @@ public class KafkaProperties {
 			this.ackTime = ackTime;
 		}
 
-		public boolean getBatchListener() {
-			return this.batchListener;
-		}
-
-		public void setBatchListener(boolean batchListener) {
-			this.batchListener = batchListener;
-		}
 	}
 
 	public static class Ssl {

spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -329,6 +329,10 @@
     "name": "spring.kafka.jaas.control-flag",
     "defaultValue": "required"
   },
+  {
+    "name": "spring.kafka.listener.type",
+    "defaultValue": "single"
+  },
   {
     "name": "spring.mobile.devicedelegatingviewresolver.enabled",
     "type": "java.lang.Boolean",

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/kafka/KafkaAutoConfigurationTests.java

@@ -176,7 +176,7 @@ public class KafkaAutoConfigurationTests {
 				"spring.kafka.listener.ack-time=456",
 				"spring.kafka.listener.concurrency=3",
 				"spring.kafka.listener.poll-timeout=2000",
-				"spring.kafka.listener.batch-listener=true",
+				"spring.kafka.listener.type=batch",
 				"spring.kafka.jaas.enabled=true", "spring.kafka.jaas.login-module=foo",
 				"spring.kafka.jaas.control-flag=REQUISITE",
 				"spring.kafka.jaas.options.useKeyTab=true");

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -986,7 +986,7 @@ content into your application; rather pick only the properties that you need.
 	spring.kafka.listener.ack-time= # Time in milliseconds between offset commits when ackMode is "TIME" or "COUNT_TIME".
 	spring.kafka.listener.concurrency= # Number of threads to run in the listener containers.
 	spring.kafka.listener.poll-timeout= # Timeout in milliseconds to use when polling the consumer.
-	spring.kafka.listener.batch-listener= # If true listener container factory will be configured to create batch listener.
+	spring.kafka.listener.type=single # Listener type.
 	spring.kafka.producer.acks= # Number of acknowledgments the producer requires the leader to have received before considering a request complete.
 	spring.kafka.producer.batch-size= # Number of records to batch before sending.
 	spring.kafka.producer.bootstrap-servers= # Comma-delimited list of host:port pairs to use for establishing the initial connection to the Kafka cluster.