Polish "Add Kafka Streams auto-configuration"

Closes gh-14021

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

@@ -1105,7 +1105,8 @@ content into your application. Rather, pick only the properties that you need.
 	spring.kafka.ssl.trust-store-location= # Location of the trust store file.
 	spring.kafka.ssl.trust-store-password= # Store password for the trust store file.
 	spring.kafka.ssl.trust-store-type= # Type of the trust store.
-	spring.kafka.streams.auto-startup= # Whether or not to auto-start the streams factory bean.
+	spring.kafka.streams.application-id = # Kafka streams application.id property; default spring.application.name.
+	spring.kafka.streams.auto-startup=true # Whether or not to auto-start the streams factory bean.
 	spring.kafka.streams.bootstrap-servers= # Comma-delimited list of host:port pairs to use for establishing the initial connection to the Kafka cluster. Overrides the global property, for streams.
 	spring.kafka.streams.cache-max-bytes-buffering= # Maximum number of memory bytes to be used for buffering across all threads.
 	spring.kafka.streams.client-id= # ID to pass to the server when making requests. Used for server-side logging.

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -5634,44 +5634,34 @@ The following component creates a listener endpoint on the `someTopic` topic:
 	}
 ----
 
-[[boot-deatures-kafka-streams]]
+[[boot-features-kafka-streams]]
 ==== Kafka Streams
-
 Spring for Apache Kafka provides a factory bean to create a `StreamsBuilder` object and
-manage the lifecycle of its streams; the factory bean is created when
-`@EnableKafkaStreams` is present on a `@Configuration` class.
-The factory bean requires a `KafkaStreamsConfiguration` object for streams configuration.
+manage the lifecycle of its streams. Spring Boot auto-configures the required
+`KafkaStreamsConfiguration` bean as long as `kafka-streams` in on the classpath and kafka
+streams is enabled via the @EnableKafkaStreams` annotation.
 
-If Spring Boot detects the `kafka-streams` jar on the classpath, it will auto-configure
-the `KafkaStreamsConfiguration` bean from the `KafkaProperties` object as well as enabling
-the creation of the factory bean by spring-kafka.
+Enabling Kafka Streams means that the application id and bootstrap servers must be set.
+The former can be configured using `spring.kafka.streams.application-id`, defaulting to
+`spring.application.name` if not set. The later can be set globally or
+specifically overridden just for streams.
 
-There are two required Kafka properties for streams (`bootstrap.servers` and
-`application.id`); by default, the `application.id` is set to the `spring.application.name`
-property, if present.
-The `bootstrap.servers` can be set globally or specifically overridden just for streams.
-Several other properties are specifically available as boot properties; other arbitrary
-Kafka properties can be set using the `spring.kafka.streams.properties` property.
-See <<boot-features-kafka-extra-props>> for more information.
+Several additional properties are available using dedicated properties; other arbitrary
+Kafka properties can be set using the `spring.kafka.streams.properties` namespace. See
+also <<boot-features-kafka-extra-props>> for more information.
 
-To use the factory bean, simply wire its `StreamsBuilder` into your `@Bean` s.
+To use the factory bean, simply wire `StreamsBuilder` into your `@Bean` as shown in the
+following example:
 
-====
-[source, java]
+[source,java,indent=0]
 ----
-@Bean
-public KStream<Integer, String> kStream(StreamsBuilder streamsBuilder) {
-	KStream<Integer, String> stream = streamsBuilder.stream("ks1In");
-	stream.map((k, v) -> new KeyValue(k, v.toUpperCase()))
-			.to("ks1Out", Produced.with(Serdes.Integer(), new JsonSerde<>()));
-	return stream;
-}
+include::{code-examples}/kafka/KafkaStreamsBeanExample.java[tag=configuration]
 ----
-====
 
-By default, the factory bean `autoStartup` property is false; to automatically start the
-streams managed by the `StreamsBuilder` object it creates, set property
-`spting.kafka.streams.auto-startup=true`.
+By default, the streams managed by the `StreamBuilder` object it creates are started
+automatically. You can customize this behaviour using the
+`spring.kafka.streams.auto-startup` property.
+
 
 
 [[boot-features-kafka-extra-props]]

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/kafka/KafkaStreamsBeanExample.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2012-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 org.springframework.boot.docs.kafka;
+
+import org.apache.kafka.common.serialization.Serdes;
+import org.apache.kafka.streams.KeyValue;
+import org.apache.kafka.streams.StreamsBuilder;
+import org.apache.kafka.streams.kstream.KStream;
+import org.apache.kafka.streams.kstream.Produced;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.annotation.EnableKafkaStreams;
+import org.springframework.kafka.support.serializer.JsonSerde;
+
+/**
+ * Example to show usage of {@link StreamsBuilder}.
+ *
+ * @author Stephane Nicoll
+ */
+public class KafkaStreamsBeanExample {
+
+	// tag::configuration[]
+	@Configuration
+	@EnableKafkaStreams
+	static class KafkaStreamsExampleConfiguration {
+
+		@Bean
+		public KStream<Integer, String> kStream(StreamsBuilder streamsBuilder) {
+			KStream<Integer, String> stream = streamsBuilder.stream("ks1In");
+			stream.map((k, v) -> new KeyValue(k, v.toUpperCase())).to("ks1Out",
+					Produced.with(Serdes.Integer(), new JsonSerde<>()));
+			return stream;
+		}
+
+	}
+	// end::configuration[]
+
+}