GH-2391: Add Kraft Version of EmbeddedKafkaBroker

Resolves #2391

* Kraft by default; polishing.
* Fix typo.

Author: garyrussell

spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc

@@ -3,6 +3,16 @@
 
 The `spring-kafka-test` jar contains some useful utilities to assist with testing your applications.
 
+[[ekb]]
+== EmbeddedKafkaBroker
+
+Two implementations are provided:
+
+* `EmbeddedKafkaZKBroker` - legacy implementation which starts an embedded `Zookeeper` instance.
+* `EmbeddedKafkaKraftBroker` - (default) uses Kraft instead of `Zookeeper` in combined controller and broker modes (since 3.1)
+
+There are several techniques to configure the broker as discussed in the following sections.
+
 [[ktu]]
 == KafkaTestUtils
 
@@ -47,7 +57,7 @@ If this is not possible for some reason, note that the `consumeFromEmbeddedTopic
 Since it does not have access to the consumer properties, you must use the overloaded method that takes a `seekToEnd` boolean parameter to seek to the end instead of the beginning.
 ====
 
-A JUnit 4 `@Rule` wrapper for the `EmbeddedKafkaBroker` is provided to create an embedded Kafka and an embedded Zookeeper server.
+A JUnit 4 `@Rule` wrapper for the `EmbeddedKafkaZKBroker` is provided to create an embedded Kafka and an embedded Zookeeper server.
 (See xref:testing.adoc#embedded-kafka-annotation[@EmbeddedKafka Annotation] for information about using `@EmbeddedKafka` with JUnit 5).
 The following listing shows the signatures of those methods:
 
@@ -72,6 +82,8 @@ public EmbeddedKafkaRule(int count, boolean controlledShutdown, String... topics
 public EmbeddedKafkaRule(int count, boolean controlledShutdown, int partitions, String... topics) { ... }
 ----
 
+NOTE: The `EmbeddedKafkaKraftBroker` is not supported with JUnit4.
+
 The `EmbeddedKafkaBroker` class has a utility method that lets you consume for all the topics it created.
 The following example shows how to use it:
 
@@ -162,7 +174,7 @@ You can use the same broker for multiple test classes with something similar to
 ----
 public final class EmbeddedKafkaHolder {
 
-    private static EmbeddedKafkaBroker embeddedKafka = new EmbeddedKafkaBroker(1, false)
+    private static EmbeddedKafkaBroker embeddedKafka = new EmbeddedKafkaZKBroker(1, false)
             .brokerListProperty("spring.kafka.bootstrap-servers");
 
     private static boolean started;
@@ -216,7 +228,8 @@ In addition, these properties can be provided:
 - `spring.kafka.embedded.ports` - ports (comma-separated value) for every Kafka broker to start, `0` if random port is a preferred; the number of values must be equal to the `count` mentioned above;
 - `spring.kafka.embedded.topics` - topics (comma-separated value) to create in the started Kafka cluster;
 - `spring.kafka.embedded.partitions` - number of partitions to provision for the created topics;
-- `spring.kafka.embedded.broker.properties.location` - the location of the file for additional Kafka broker configuration properties; the value of this property must follow the Spring resource abstraction pattern.
+- `spring.kafka.embedded.broker.properties.location` - the location of the file for additional Kafka broker configuration properties; the value of this property must follow the Spring resource abstraction pattern;
+- `spring.kafka.embedded.kraft` - when false, use an `EmbeddedKafkaZKBroker` instead of an `EmbeddedKafkaKraftBroker`.
 
 Essentially these properties mimic some of the `@EmbeddedKafka` attributes.
 
@@ -283,6 +296,8 @@ public class KafkaStreamsTests {
 
 Starting with version 2.2.4, you can also use the `@EmbeddedKafka` annotation to specify the Kafka ports property.
 
+Starting with version 3.1; set the `kraft` property to `false` to use an `EmbeddedKafkaZKBroker` instead of an `EmbeddedKafkaKraftBroker`.
+
 The following example sets the `topics`, `brokerProperties`, and `brokerPropertiesLocation` attributes of `@EmbeddedKafka` support property placeholder resolutions:
 
 [source, java]

spring-kafka-docs/src/main/antora/modules/ROOT/pages/whats-new.adoc

@@ -7,8 +7,13 @@
 This section covers the changes made from version 3.0 to version 3.1.
 For changes in earlier version, see xref:appendix/change-history.adoc[Change History].
 
-[[x30-kafka-client]]
+[[x31-kafka-client]]
 === Kafka Client Version
 
 This version requires the 3.5.1 `kafka-clients`.
 
+[[x31-ekb]]
+=== EmbeddedKafkaBroker
+
+An additional implementation is now provided to use `Kraft` instead of Zookeeper.
+See <<ekb>> for more information.