Polish "Add support for arbitrary producer/consumer Kafka properties"

Closes gh-9775

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

@@ -66,7 +66,7 @@ public class KafkaProperties {
 	 * Additional properties, common to producers and consumers, used to configure the
 	 * client.
 	 */
-	private Map<String, String> properties = new HashMap<>();
+	private final Map<String, String> properties = new HashMap<>();
 
 	private final Consumer consumer = new Consumer();
 
@@ -100,10 +100,6 @@ public class KafkaProperties {
 		return this.properties;
 	}
 
-	public void setProperties(Map<String, String> properties) {
-		this.properties = properties;
-	}
-
 	public Consumer getConsumer() {
 		return this.consumer;
 	}
@@ -270,9 +266,9 @@ public class KafkaProperties {
 		private Integer maxPollRecords;
 
 		/**
-		 * Additional properties used to configure the client.
+		 * Additional consumer-specific properties used to configure the client.
 		 */
-		private Map<String, String> properties = new HashMap<>();
+		private final Map<String, String> properties = new HashMap<>();
 
 		public Ssl getSsl() {
 			return this.ssl;
@@ -378,10 +374,6 @@ public class KafkaProperties {
 			return this.properties;
 		}
 
-		public void setProperties(Map<String, String> properties) {
-			this.properties = properties;
-		}
-
 		public Map<String, Object> buildProperties() {
 			Map<String, Object> properties = new HashMap<>();
 			if (this.autoCommitInterval != null) {
@@ -508,9 +500,9 @@ public class KafkaProperties {
 		private Integer retries;
 
 		/**
-		 * Additional properties used to configure the client.
+		 * Additional producer-specific properties used to configure the client.
 		 */
-		private Map<String, String> properties = new HashMap<>();
+		private final Map<String, String> properties = new HashMap<>();
 
 		public Ssl getSsl() {
 			return this.ssl;
@@ -592,10 +584,6 @@ public class KafkaProperties {
 			return this.properties;
 		}
 
-		public void setProperties(Map<String, String> properties) {
-			this.properties = properties;
-		}
-
 		public Map<String, Object> buildProperties() {
 			Map<String, Object> properties = new HashMap<>();
 			if (this.acks != null) {

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

@@ -968,7 +968,7 @@ content into your application; rather pick only the properties that you need.
 	spring.kafka.consumer.heartbeat-interval= # Expected time in milliseconds between heartbeats to the consumer coordinator.
 	spring.kafka.consumer.key-deserializer= # Deserializer class for keys.
 	spring.kafka.consumer.max-poll-records= # Maximum number of records returned in a single call to poll().
-	spring.kafka.consumer.properties.*= # Additional properties used to configure the client.
+	spring.kafka.consumer.properties.*= # Additional consumer-specific properties used to configure the client.
 	spring.kafka.consumer.ssl.key-password= # Password of the private key in the key store file.
 	spring.kafka.consumer.ssl.keystore-location= # Location of the key store file.
 	spring.kafka.consumer.ssl.keystore-password= # Store password for the key store file.
@@ -992,7 +992,7 @@ content into your application; rather pick only the properties that you need.
 	spring.kafka.producer.client-id= # Id to pass to the server when making requests; used for server-side logging.
 	spring.kafka.producer.compression-type= # Compression type for all data generated by the producer.
 	spring.kafka.producer.key-serializer= # Serializer class for keys.
-	spring.kafka.producer.properties.*= # Additional properties used to configure the client.
+	spring.kafka.producer.properties.*= # Additional producer-specific properties used to configure the client.
 	spring.kafka.producer.retries= # When greater than zero, enables retrying of failed sends.
 	spring.kafka.producer.ssl.key-password= # Password of the private key in the key store file.
 	spring.kafka.producer.ssl.keystore-location= # Location of the key store file.

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

@@ -5121,9 +5121,12 @@ are not directly supported, use the following:
 	spring,kafka.producer.properties.baz.qux=fiz
 ----
 
-This sets the common `foo.bar` Kafka property to `baz` (applies to both producers and consumers), the consumer `fiz.buz` property to `qux` and the `baz.qux` producer property to `fiz`.
+This sets the common `foo.bar` Kafka property to `baz` (applies to both producers and
+consumers), the consumer `fiz.buz` property to `qux` and the `baz.qux` producer property
+to `fiz`.
 
-IMPORTANT: Properties set in this way will override properties that are in the subset that boot explicitly supports.
+IMPORTANT: Properties set in this way will override any configuration item that Spring
+Boot explicitly supports.
 
 [[boot-features-resttemplate]]
 == Calling REST services with '`RestTemplate`'