Introduce Kotlin Serialization auto-configuration

See gh-46546

Signed-off-by: Dmitry Sulman <dmitry.sulman@gmail.com>

buildSrc/src/main/java/org/springframework/boot/build/context/properties/DocumentConfigurationProperties.java

@@ -118,6 +118,7 @@ public abstract class DocumentConfigurationProperties extends DefaultTask {
 	private void jsonPrefixes(Config config) {
 		config.accept("spring.jackson");
 		config.accept("spring.gson");
+		config.accept("spring.kotlin-serialization");
 	}
 
 	private void dataPrefixes(Config config) {

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/features/json.adoc

@@ -6,6 +6,7 @@ Spring Boot provides integration with three JSON mapping libraries:
 - Gson
 - Jackson 3
 - JSON-B
+- Kotlin Serialization
 
 Jackson is the preferred and default library.
 
@@ -68,3 +69,12 @@ To take more control, one or more javadoc:org.springframework.boot.autoconfigure
 Auto-configuration for JSON-B is provided.
 When the JSON-B API and an implementation are on the classpath a javadoc:jakarta.json.bind.Jsonb[] bean will be automatically configured.
 The preferred JSON-B implementation is Eclipse Yasson for which dependency management is provided.
+
+
+
+[[features.json.kotlin-serialization]]
+== Kotlin Serialization
+
+Auto-configuration for Kotlin Serialization is provided.
+When `kotlinx-serialization-json` is on the classpath a https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/-json/[Json] bean is automatically configured.
+Several `+spring.kotlin-serialization.*+` configuration properties are provided for customizing the configuration.

module/spring-boot-autoconfigure-classic-modules/build.gradle

@@ -154,6 +154,9 @@ dependencies {
 	api(project(":module:spring-boot-kafka")) {
 		transitive = false
 	}
+	api(project(":module:spring-boot-kotlin-serialization")) {
+		transitive = false
+	}
 	api(project(":module:spring-boot-ldap")) {
 		transitive = false
 	}

module/spring-boot-http-converter/build.gradle

@@ -34,6 +34,7 @@ dependencies {
 	optional(project(":module:spring-boot-gson"))
 	optional(project(":module:spring-boot-jackson"))
 	optional(project(":module:spring-boot-jsonb"))
+	optional(project(":module:spring-boot-kotlin-serialization"))
 	optional("com.google.code.gson:gson")
 	optional("jakarta.json.bind:jakarta.json.bind-api")
 	optional("org.springframework:spring-webmvc")

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/GsonHttpMessageConvertersConfiguration.java

@@ -91,6 +91,12 @@ class GsonHttpMessageConvertersConfiguration {
 
 		}
 
+		@ConditionalOnProperty(name = HttpMessageConvertersAutoConfiguration.PREFERRED_MAPPER_PROPERTY,
+				havingValue = "kotlin-serialization")
+		static class KotlinxSerialization {
+
+		}
+
 	}
 
 }

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/HttpMessageConverters.java

@@ -71,9 +71,11 @@ public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>>
 		MultiValueMap<Class<?>, Class<?>> equivalentConverters = new LinkedMultiValueMap<>();
 		putIfExists(equivalentConverters, "org.springframework.http.converter.json.JacksonJsonHttpMessageConverter",
 				"org.springframework.http.converter.json.MappingJackson2HttpMessageConverter",
-				"org.springframework.http.converter.json.GsonHttpMessageConverter");
+				"org.springframework.http.converter.json.GsonHttpMessageConverter",
+				"org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter");
 		putIfExists(equivalentConverters, "org.springframework.http.converter.json.MappingJackson2HttpMessageConverter",
-				"org.springframework.http.converter.json.GsonHttpMessageConverter");
+				"org.springframework.http.converter.json.GsonHttpMessageConverter",
+				"org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter");
 		EQUIVALENT_CONVERTERS = CollectionUtils.unmodifiableMultiValueMap(equivalentConverters);
 	}
 

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/HttpMessageConvertersAutoConfiguration.java

@@ -45,15 +45,17 @@ import org.springframework.http.converter.StringHttpMessageConverter;
  * @author Sebastien Deleuze
  * @author Stephane Nicoll
  * @author Eddú Meléndez
+ * @author Dmitry Sulman
  * @since 4.0.0
  */
 @AutoConfiguration(afterName = { "org.springframework.boot.jackson.autoconfigure.JacksonAutoConfiguration",
 		"org.springframework.boot.jsonb.autoconfigure.JsonbAutoConfiguration",
-		"org.springframework.boot.gson.autoconfigure.GsonAutoConfiguration" })
+		"org.springframework.boot.gson.autoconfigure.GsonAutoConfiguration",
+		"org.springframework.boot.kotlin.serialization.autoconfigure.KotlinSerializationAutoConfiguration" })
 @ConditionalOnClass(HttpMessageConverter.class)
 @Conditional(NotReactiveWebApplicationCondition.class)
 @Import({ JacksonHttpMessageConvertersConfiguration.class, GsonHttpMessageConvertersConfiguration.class,
-		JsonbHttpMessageConvertersConfiguration.class })
+		JsonbHttpMessageConvertersConfiguration.class, KotlinSerializationHttpMessageConvertersConfiguration.class })
 public final class HttpMessageConvertersAutoConfiguration {
 
 	static final String PREFERRED_MAPPER_PROPERTY = "spring.http.converters.preferred-json-mapper";

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/JsonbHttpMessageConvertersConfiguration.java

@@ -23,6 +23,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.autoconfigure.condition.NoneNestedConditions;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
@@ -66,8 +67,32 @@ class JsonbHttpMessageConvertersConfiguration {
 
 		}
 
-		@ConditionalOnMissingBean({ JacksonJsonHttpMessageConverter.class, GsonHttpMessageConverter.class })
+		@Conditional(JacksonAndGsonAndKotlinSerializationMissingCondition.class)
-		static class JacksonAndGsonMissing {
+		static class JacksonAndGsonAndKotlinSerializationMissing {
+
+		}
+
+	}
+
+	private static class JacksonAndGsonAndKotlinSerializationMissingCondition extends NoneNestedConditions {
+
+		JacksonAndGsonAndKotlinSerializationMissingCondition() {
+			super(ConfigurationPhase.REGISTER_BEAN);
+		}
+
+		@ConditionalOnBean(JacksonJsonHttpMessageConverter.class)
+		static class JacksonAvailable {
+
+		}
+
+		@ConditionalOnBean(GsonHttpMessageConverter.class)
+		static class GsonAvailable {
+
+		}
+
+		@ConditionalOnProperty(name = HttpMessageConvertersAutoConfiguration.PREFERRED_MAPPER_PROPERTY,
+				havingValue = "kotlin-serialization")
+		static class KotlinxPreferred {
 
 		}
 

module/spring-boot-http-converter/src/main/java/org/springframework/boot/http/converter/autoconfigure/KotlinSerializationHttpMessageConvertersConfiguration.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.http.converter.autoconfigure;
+
+import kotlinx.serialization.json.Json;
+
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
+
+/**
+ * Configuration for HTTP message converters that use Kotlin Serialization.
+ *
+ * @author Dmitry Sulman
+ */
+@Configuration(proxyBeanMethods = false)
+@ConditionalOnClass(Json.class)
+class KotlinSerializationHttpMessageConvertersConfiguration {
+
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnBean(Json.class)
+	@ConditionalOnProperty(name = HttpMessageConvertersAutoConfiguration.PREFERRED_MAPPER_PROPERTY,
+			havingValue = "kotlin-serialization")
+	static class KotlinSerializationHttpMessageConverterConfiguration {
+
+		@Bean
+		@ConditionalOnMissingBean
+		KotlinSerializationJsonHttpMessageConverter kotlinSerializationJsonHttpMessageConverter(Json json) {
+			return new KotlinSerializationJsonHttpMessageConverter(json);
+		}
+
+	}
+
+}

module/spring-boot-http-converter/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -4,7 +4,7 @@
       "name": "spring.http.converters.preferred-json-mapper",
       "type": "java.lang.String",
       "defaultValue": "jackson",
-      "description": "Preferred JSON mapper to use for HTTP message conversion. By default, auto-detected according to the environment. Supported values are 'jackson', 'gson', and 'jsonb'. When other json mapping libraries (such as kotlinx.serialization) are present, use a custom HttpMessageConverters bean to control the preferred mapper."
+      "description": "Preferred JSON mapper to use for HTTP message conversion. By default, auto-detected according to the environment. Supported values are 'jackson', 'gson', 'jsonb' and 'kotlin-serialization'. When other json mapping libraries are present, use a custom HttpMessageConverters bean to control the preferred mapper."
     }
   ],
   "hints": [
@@ -19,6 +19,9 @@
         },
         {
           "value": "jsonb"
+        },
+        {
+          "value": "kotlin-serialization"
         }
       ],
       "providers": [

module/spring-boot-http-converter/src/test/java/org/springframework/boot/http/converter/autoconfigure/HttpMessageConvertersAutoConfigurationTests.java

@@ -21,6 +21,7 @@ import java.nio.charset.StandardCharsets;
 import com.google.gson.Gson;
 import jakarta.json.bind.Jsonb;
 import jakarta.json.bind.JsonbBuilder;
+import kotlinx.serialization.json.Json;
 import org.junit.jupiter.api.Test;
 import tools.jackson.databind.ObjectMapper;
 import tools.jackson.databind.json.JsonMapper;
@@ -46,6 +47,7 @@ import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.json.GsonHttpMessageConverter;
 import org.springframework.http.converter.json.JacksonJsonHttpMessageConverter;
 import org.springframework.http.converter.json.JsonbHttpMessageConverter;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 import org.springframework.http.converter.xml.JacksonXmlHttpMessageConverter;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -61,6 +63,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Eddú Meléndez
  * @author Moritz Halbritter
  * @author Sebastien Deleuze
+ * @author Dmitry Sulman
  */
 class HttpMessageConvertersAutoConfigurationTests {
 
@@ -128,6 +131,7 @@ class HttpMessageConvertersAutoConfigurationTests {
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, GsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JacksonJsonHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 		});
 	}
 
@@ -159,9 +163,40 @@ class HttpMessageConvertersAutoConfigurationTests {
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, JsonbHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(GsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JacksonJsonHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 		});
 	}
 
+	@Test
+	void kotlinSerializationNotAvailable() {
+		this.contextRunner.run((context) -> {
+			assertThat(context).doesNotHaveBean(Json.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
+		});
+	}
+
+	@Test
+	void kotlinSerializationCustomConverter() {
+		this.contextRunner.withUserConfiguration(KotlinSerializationConverterConfig.class)
+			.withBean(Json.class, () -> Json.Default)
+			.run(assertConverter(KotlinSerializationJsonHttpMessageConverter.class,
+					"customKotlinSerializationJsonHttpMessageConverter"));
+	}
+
+	@Test
+	void kotlinSerializationCanBePreferred() {
+		allOptionsRunner().withPropertyValues("spring.http.converters.preferred-json-mapper:kotlin-serialization")
+			.run((context) -> {
+				assertConverterBeanExists(context, KotlinSerializationJsonHttpMessageConverter.class,
+						"kotlinSerializationJsonHttpMessageConverter");
+				assertConverterBeanRegisteredWithHttpMessageConverters(context,
+						KotlinSerializationJsonHttpMessageConverter.class);
+				assertThat(context).doesNotHaveBean(GsonHttpMessageConverter.class);
+				assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+				assertThat(context).doesNotHaveBean(JacksonJsonHttpMessageConverter.class);
+			});
+	}
+
 	@Test
 	void stringDefaultConverter() {
 		this.contextRunner.run(assertConverter(StringHttpMessageConverter.class, "stringHttpMessageConverter"));
@@ -205,6 +240,7 @@ class HttpMessageConvertersAutoConfigurationTests {
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, JacksonJsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(GsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 		});
 	}
 
@@ -215,6 +251,7 @@ class HttpMessageConvertersAutoConfigurationTests {
 				assertConverterBeanExists(context, GsonHttpMessageConverter.class, "gsonHttpMessageConverter");
 				assertConverterBeanRegisteredWithHttpMessageConverters(context, GsonHttpMessageConverter.class);
 				assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+				assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 			});
 	}
 
@@ -266,7 +303,8 @@ class HttpMessageConvertersAutoConfigurationTests {
 	private ApplicationContextRunner allOptionsRunner() {
 		return this.contextRunner.withBean(Gson.class)
 			.withBean(JsonMapper.class)
-			.withBean(Jsonb.class, JsonbBuilder::create);
+			.withBean(Jsonb.class, JsonbBuilder::create)
+			.withBean(Json.class, () -> Json.Default);
 	}
 
 	private ContextConsumer<AssertableApplicationContext> assertConverter(
@@ -364,6 +402,16 @@ class HttpMessageConvertersAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class KotlinSerializationConverterConfig {
+
+		@Bean
+		KotlinSerializationJsonHttpMessageConverter customKotlinSerializationJsonHttpMessageConverter(Json json) {
+			return new KotlinSerializationJsonHttpMessageConverter(json);
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class StringConverterConfig {
 

module/spring-boot-http-converter/src/test/java/org/springframework/boot/http/converter/autoconfigure/HttpMessageConvertersTests.java

@@ -31,6 +31,7 @@ import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.cbor.JacksonCborHttpMessageConverter;
 import org.springframework.http.converter.json.GsonHttpMessageConverter;
 import org.springframework.http.converter.json.JacksonJsonHttpMessageConverter;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
 import org.springframework.http.converter.xml.JacksonXmlHttpMessageConverter;
 
@@ -88,6 +89,25 @@ class HttpMessageConvertersTests {
 				JacksonJsonHttpMessageConverter.class);
 	}
 
+	@Test
+	void addBeforeExistingAnotherEquivalentConverter() {
+		KotlinSerializationJsonHttpMessageConverter converter1 = new KotlinSerializationJsonHttpMessageConverter();
+		HttpMessageConverters converters = new HttpMessageConverters(converter1);
+		Stream<Class<?>> converterClasses = converters.getConverters().stream().map(HttpMessageConverter::getClass);
+		assertThat(converterClasses).containsSequence(KotlinSerializationJsonHttpMessageConverter.class,
+				JacksonJsonHttpMessageConverter.class);
+	}
+
+	@Test
+	void addBeforeExistingMultipleEquivalentConverters() {
+		GsonHttpMessageConverter converter1 = new GsonHttpMessageConverter();
+		KotlinSerializationJsonHttpMessageConverter converter2 = new KotlinSerializationJsonHttpMessageConverter();
+		HttpMessageConverters converters = new HttpMessageConverters(converter1, converter2);
+		Stream<Class<?>> converterClasses = converters.getConverters().stream().map(HttpMessageConverter::getClass);
+		assertThat(converterClasses).containsSequence(GsonHttpMessageConverter.class,
+				KotlinSerializationJsonHttpMessageConverter.class, JacksonJsonHttpMessageConverter.class);
+	}
+
 	@Test
 	void addNewConverters() {
 		HttpMessageConverter<?> converter1 = mock(HttpMessageConverter.class);

module/spring-boot-kotlin-serialization/build.gradle

@@ -0,0 +1,48 @@
+import org.springframework.boot.build.autoconfigure.CheckAutoConfigurationClasses
+
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.
+ */
+
+plugins {
+	id "java-library"
+	id "org.jetbrains.kotlin.jvm"
+	id "org.jetbrains.kotlin.plugin.serialization"
+	id "org.springframework.boot.auto-configuration"
+	id "org.springframework.boot.configuration-properties"
+	id "org.springframework.boot.deployed"
+	id "org.springframework.boot.optional-dependencies"
+}
+
+description = "Spring Boot Kotlin Serialization"
+
+dependencies {
+	api(project(":core:spring-boot"))
+	api("org.jetbrains.kotlinx:kotlinx-serialization-json")
+
+	optional(project(":core:spring-boot-autoconfigure"))
+
+	testImplementation(project(":core:spring-boot-test"))
+	testImplementation(project(":test-support:spring-boot-test-support"))
+
+	testRuntimeOnly("ch.qos.logback:logback-classic")
+	testRuntimeOnly("org.jetbrains.kotlin:kotlin-reflect")
+}
+
+tasks.named("checkAutoConfigurationClasses", CheckAutoConfigurationClasses.class) {
+	doFirst {
+		classpath = classpath.filter { !it.path.contains('/build/classes/kotlin/main') }
+	}
+}

module/spring-boot-kotlin-serialization/src/main/java/org/springframework/boot/kotlin/serialization/autoconfigure/KotlinSerializationAutoConfiguration.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.kotlin.serialization.autoconfigure;
+
+import java.util.List;
+import java.util.function.Consumer;
+
+import kotlin.Unit;
+import kotlin.jvm.functions.Function1;
+import kotlinx.serialization.json.Json;
+import kotlinx.serialization.json.JsonBuilder;
+import kotlinx.serialization.json.JsonKt;
+import kotlinx.serialization.json.JsonNamingStrategy;
+
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.context.properties.PropertyMapper;
+import org.springframework.context.annotation.Bean;
+import org.springframework.core.Ordered;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for Kotlin Serialization.
+ *
+ * @author Dmitry Sulman
+ * @since 4.0.0
+ */
+@AutoConfiguration
+@ConditionalOnClass(Json.class)
+@EnableConfigurationProperties(KotlinSerializationProperties.class)
+public final class KotlinSerializationAutoConfiguration {
+
+	@Bean
+	@ConditionalOnMissingBean
+	Json kotlinSerializationJson(List<KotlinSerializationJsonBuilderCustomizer> customizers) {
+		Function1<JsonBuilder, Unit> builderAction = (jsonBuilder) -> {
+			customizers.forEach((c) -> c.customize(jsonBuilder));
+			return Unit.INSTANCE;
+		};
+		return JsonKt.Json(Json.Default, builderAction);
+	}
+
+	@Bean
+	StandardKotlinSerializationJsonBuilderCustomizer standardKotlinSerializationJsonBuilderCustomizer(
+			KotlinSerializationProperties kotlinSerializationProperties) {
+		return new StandardKotlinSerializationJsonBuilderCustomizer(kotlinSerializationProperties);
+	}
+
+	static final class StandardKotlinSerializationJsonBuilderCustomizer
+			implements KotlinSerializationJsonBuilderCustomizer, Ordered {
+
+		private final KotlinSerializationProperties properties;
+
+		StandardKotlinSerializationJsonBuilderCustomizer(KotlinSerializationProperties properties) {
+			this.properties = properties;
+		}
+
+		@Override
+		public int getOrder() {
+			return 0;
+		}
+
+		@Override
+		public void customize(JsonBuilder jsonBuilder) {
+			KotlinSerializationProperties properties = this.properties;
+			PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
+			map.from(properties::getNamingStrategy).to(setNamingStrategy(jsonBuilder));
+			map.from(properties::getPrettyPrint).to(jsonBuilder::setPrettyPrint);
+			map.from(properties::getLenient).to(jsonBuilder::setLenient);
+			map.from(properties::getIgnoreUnknownKeys).to(jsonBuilder::setIgnoreUnknownKeys);
+			map.from(properties::getEncodeDefaults).to(jsonBuilder::setEncodeDefaults);
+			map.from(properties::getExplicitNulls).to(jsonBuilder::setExplicitNulls);
+			map.from(properties::getCoerceInputValues).to(jsonBuilder::setCoerceInputValues);
+			map.from(properties::getAllowStructuredMapKeys).to(jsonBuilder::setAllowStructuredMapKeys);
+			map.from(properties::getAllowSpecialFloatingPointValues)
+				.to(jsonBuilder::setAllowSpecialFloatingPointValues);
+			map.from(properties::getClassDiscriminator).to(jsonBuilder::setClassDiscriminator);
+			map.from(properties::getClassDiscriminatorMode).to(jsonBuilder::setClassDiscriminatorMode);
+			map.from(properties::getDecodeEnumsCaseInsensitive).to(jsonBuilder::setDecodeEnumsCaseInsensitive);
+			map.from(properties::getUseAlternativeNames).to(jsonBuilder::setUseAlternativeNames);
+			map.from(properties::getAllowTrailingComma).to(jsonBuilder::setAllowTrailingComma);
+			map.from(properties::getAllowComments).to(jsonBuilder::setAllowComments);
+		}
+
+		private Consumer<KotlinSerializationProperties.JsonNamingStrategy> setNamingStrategy(JsonBuilder builder) {
+			return (strategy) -> {
+				JsonNamingStrategy namingStrategy = switch (strategy) {
+					case SNAKE_CASE -> JsonNamingStrategy.Builtins.getSnakeCase();
+					case KEBAB_CASE -> JsonNamingStrategy.Builtins.getKebabCase();
+				};
+				builder.setNamingStrategy(namingStrategy);
+			};
+		}
+
+	}
+
+}

module/spring-boot-kotlin-serialization/src/main/java/org/springframework/boot/kotlin/serialization/autoconfigure/KotlinSerializationJsonBuilderCustomizer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.kotlin.serialization.autoconfigure;
+
+import kotlinx.serialization.json.Json;
+import kotlinx.serialization.json.JsonBuilder;
+
+/**
+ * Callback interface that can be implemented by beans wishing to further customize the
+ * {@link Json} through {@link JsonBuilder} retaining its default configuration.
+ *
+ * @author Dmitry Sulman
+ * @since 4.0.0
+ */
+@FunctionalInterface
+public interface KotlinSerializationJsonBuilderCustomizer {
+
+	/**
+	 * Customize the Kotlin Serialization {@link Json} through {@link JsonBuilder}.
+	 * @param jsonBuilder the {@link JsonBuilder} to customize
+	 */
+	void customize(JsonBuilder jsonBuilder);
+
+}

module/spring-boot-kotlin-serialization/src/main/java/org/springframework/boot/kotlin/serialization/autoconfigure/KotlinSerializationProperties.java

@@ -0,0 +1,258 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.kotlin.serialization.autoconfigure;
+
+import kotlinx.serialization.json.ClassDiscriminatorMode;
+import kotlinx.serialization.json.Json;
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Configuration properties to configure Kotlin Serialization {@link Json}.
+ *
+ * @author Dmitry Sulman
+ * @since 4.0.0
+ */
+@ConfigurationProperties("spring.kotlin-serialization")
+public class KotlinSerializationProperties {
+
+	/**
+	 * Specifies JsonNamingStrategy that should be used for all properties in classes for
+	 * serialization and deserialization.
+	 */
+	private @Nullable JsonNamingStrategy namingStrategy;
+
+	/**
+	 * Whether resulting JSON should be pretty-printed: formatted and optimized for human
+	 * readability.
+	 */
+	private @Nullable Boolean prettyPrint;
+
+	/**
+	 * Enable lenient mode that removes JSON specification restriction (RFC-4627) and
+	 * makes parser more liberal to the malformed input.
+	 */
+	private @Nullable Boolean lenient;
+
+	/**
+	 * Whether encounters of unknown properties in the input JSON should be ignored
+	 * instead of throwing SerializationException.
+	 */
+	private @Nullable Boolean ignoreUnknownKeys;
+
+	/**
+	 * Whether default values of Kotlin properties should be encoded.
+	 */
+	private @Nullable Boolean encodeDefaults;
+
+	/**
+	 * Whether null values should be encoded for nullable properties and must be present
+	 * in JSON object during decoding.
+	 */
+	private @Nullable Boolean explicitNulls;
+
+	/**
+	 * Enable coercing incorrect JSON values.
+	 */
+	private @Nullable Boolean coerceInputValues;
+
+	/**
+	 * Enable structured objects to be serialized as map keys by changing serialized form
+	 * of the map from JSON object (key-value pairs) to flat array like [k1, v1, k2, v2].
+	 */
+	private @Nullable Boolean allowStructuredMapKeys;
+
+	/**
+	 * Whether to remove JSON specification restriction on special floating-point values
+	 * such as 'NaN' and 'Infinity' and enable their serialization and deserialization as
+	 * float literals without quotes.
+	 */
+	private @Nullable Boolean allowSpecialFloatingPointValues;
+
+	/**
+	 * Name of the class descriptor property for polymorphic serialization.
+	 */
+	private @Nullable String classDiscriminator;
+
+	/**
+	 * Defines which classes and objects should have class discriminator added to the
+	 * output.
+	 */
+	private @Nullable ClassDiscriminatorMode classDiscriminatorMode;
+
+	/**
+	 * Enable decoding enum values in a case-insensitive manner.
+	 */
+	private @Nullable Boolean decodeEnumsCaseInsensitive;
+
+	/**
+	 * Whether Json instance makes use of JsonNames annotation.
+	 */
+	private @Nullable Boolean useAlternativeNames;
+
+	/**
+	 * Whether to allow parser to accept trailing (ending) commas in JSON objects and
+	 * arrays.
+	 */
+	private @Nullable Boolean allowTrailingComma;
+
+	/**
+	 * Whether to allow parser to accept C/Java-style comments in JSON input.
+	 */
+	private @Nullable Boolean allowComments;
+
+	public @Nullable JsonNamingStrategy getNamingStrategy() {
+		return this.namingStrategy;
+	}
+
+	public void setNamingStrategy(@Nullable JsonNamingStrategy namingStrategy) {
+		this.namingStrategy = namingStrategy;
+	}
+
+	public @Nullable Boolean getPrettyPrint() {
+		return this.prettyPrint;
+	}
+
+	public void setPrettyPrint(@Nullable Boolean prettyPrint) {
+		this.prettyPrint = prettyPrint;
+	}
+
+	public @Nullable Boolean getLenient() {
+		return this.lenient;
+	}
+
+	public void setLenient(@Nullable Boolean lenient) {
+		this.lenient = lenient;
+	}
+
+	public @Nullable Boolean getIgnoreUnknownKeys() {
+		return this.ignoreUnknownKeys;
+	}
+
+	public void setIgnoreUnknownKeys(@Nullable Boolean ignoreUnknownKeys) {
+		this.ignoreUnknownKeys = ignoreUnknownKeys;
+	}
+
+	public @Nullable Boolean getEncodeDefaults() {
+		return this.encodeDefaults;
+	}
+
+	public void setEncodeDefaults(@Nullable Boolean encodeDefaults) {
+		this.encodeDefaults = encodeDefaults;
+	}
+
+	public @Nullable Boolean getExplicitNulls() {
+		return this.explicitNulls;
+	}
+
+	public void setExplicitNulls(@Nullable Boolean explicitNulls) {
+		this.explicitNulls = explicitNulls;
+	}
+
+	public @Nullable Boolean getCoerceInputValues() {
+		return this.coerceInputValues;
+	}
+
+	public void setCoerceInputValues(@Nullable Boolean coerceInputValues) {
+		this.coerceInputValues = coerceInputValues;
+	}
+
+	public @Nullable Boolean getAllowStructuredMapKeys() {
+		return this.allowStructuredMapKeys;
+	}
+
+	public void setAllowStructuredMapKeys(@Nullable Boolean allowStructuredMapKeys) {
+		this.allowStructuredMapKeys = allowStructuredMapKeys;
+	}
+
+	public @Nullable Boolean getAllowSpecialFloatingPointValues() {
+		return this.allowSpecialFloatingPointValues;
+	}
+
+	public void setAllowSpecialFloatingPointValues(@Nullable Boolean allowSpecialFloatingPointValues) {
+		this.allowSpecialFloatingPointValues = allowSpecialFloatingPointValues;
+	}
+
+	public @Nullable String getClassDiscriminator() {
+		return this.classDiscriminator;
+	}
+
+	public void setClassDiscriminator(@Nullable String classDiscriminator) {
+		this.classDiscriminator = classDiscriminator;
+	}
+
+	public @Nullable ClassDiscriminatorMode getClassDiscriminatorMode() {
+		return this.classDiscriminatorMode;
+	}
+
+	public void setClassDiscriminatorMode(@Nullable ClassDiscriminatorMode classDiscriminatorMode) {
+		this.classDiscriminatorMode = classDiscriminatorMode;
+	}
+
+	public @Nullable Boolean getDecodeEnumsCaseInsensitive() {
+		return this.decodeEnumsCaseInsensitive;
+	}
+
+	public void setDecodeEnumsCaseInsensitive(@Nullable Boolean decodeEnumsCaseInsensitive) {
+		this.decodeEnumsCaseInsensitive = decodeEnumsCaseInsensitive;
+	}
+
+	public @Nullable Boolean getUseAlternativeNames() {
+		return this.useAlternativeNames;
+	}
+
+	public void setUseAlternativeNames(@Nullable Boolean useAlternativeNames) {
+		this.useAlternativeNames = useAlternativeNames;
+	}
+
+	public @Nullable Boolean getAllowTrailingComma() {
+		return this.allowTrailingComma;
+	}
+
+	public void setAllowTrailingComma(@Nullable Boolean allowTrailingComma) {
+		this.allowTrailingComma = allowTrailingComma;
+	}
+
+	public @Nullable Boolean getAllowComments() {
+		return this.allowComments;
+	}
+
+	public void setAllowComments(@Nullable Boolean allowComments) {
+		this.allowComments = allowComments;
+	}
+
+	/**
+	 * Enum representing strategies for JSON property naming. The values correspond to
+	 * {@link kotlinx.serialization.json.JsonNamingStrategy} implementations that cannot
+	 * be directly referenced.
+	 */
+	public enum JsonNamingStrategy {
+
+		/**
+		 * Snake case strategy.
+		 */
+		SNAKE_CASE,
+
+		/**
+		 * Kebab case strategy.
+		 */
+		KEBAB_CASE
+
+	}
+
+}

module/spring-boot-kotlin-serialization/src/main/java/org/springframework/boot/kotlin/serialization/autoconfigure/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.
+ */
+
+/**
+ * Auto-configuration for Kotlin Serialization.
+ */
+@NullMarked
+package org.springframework.boot.kotlin.serialization.autoconfigure;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-kotlin-serialization/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -0,0 +1 @@
+org.springframework.boot.kotlin.serialization.autoconfigure.KotlinSerializationAutoConfiguration

module/spring-boot-kotlin-serialization/src/test/kotlin/org/springframework/boot/kotlin/serialization/autoconfigure/KotlinSerializationAutoConfigurationTests.kt

@@ -0,0 +1,321 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.kotlin.serialization.autoconfigure
+
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonNames
+import kotlinx.serialization.json.JsonNamingStrategy
+import org.assertj.core.api.Assertions.assertThatExceptionOfType
+import org.assertj.core.api.AssertionsForInterfaceTypes.assertThat
+import org.junit.jupiter.api.Test
+import org.springframework.boot.autoconfigure.AutoConfigurations
+import org.springframework.boot.test.context.FilteredClassLoader
+import org.springframework.boot.test.context.runner.ApplicationContextRunner
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+
+/**
+ * Tests for [KotlinSerializationAutoConfiguration].
+ *
+ * @author Dmitry Sulman
+ */
+class KotlinSerializationAutoConfigurationTests {
+	private val contextRunner = ApplicationContextRunner()
+		.withConfiguration(AutoConfigurations.of(KotlinSerializationAutoConfiguration::class.java))
+
+	@Test
+	fun shouldSupplyBean() {
+		this.contextRunner.run { context ->
+			assertThat(context).hasSingleBean(Json::class.java)
+		}
+	}
+
+	@Test
+	fun shouldNotSupplyBean() {
+		this.contextRunner
+			.withClassLoader(FilteredClassLoader(Json::class.java))
+			.run { context ->
+				assertThat(context).doesNotHaveBean(Json::class.java)
+			}
+	}
+
+	@Test
+	fun serializeToString() {
+		this.contextRunner.run { context ->
+			val json = context.getBean(Json::class.java)
+			assertThat(json.encodeToString(DataObject("hello")))
+				.isEqualTo("""{"stringField":"hello"}""")
+		}
+	}
+
+	@Test
+	fun deserializeFromString() {
+		this.contextRunner.run { context ->
+			val json = context.getBean(Json::class.java)
+			assertThat(json.decodeFromString<DataObject>("""{"stringField":"hello"}"""))
+				.isEqualTo(DataObject("hello"))
+		}
+	}
+
+	@Test
+	fun customJsonBean() {
+		this.contextRunner
+			.withUserConfiguration(CustomKotlinSerializationConfig::class.java)
+			.run { context ->
+				assertThat(context).hasSingleBean(Json::class.java)
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObject("hello")))
+					.isEqualTo("""{"string_field":"hello"}""")
+			}
+	}
+
+	@Test
+	fun serializeSnakeCase() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.naming-strategy=snake_case")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObject("hello")))
+					.isEqualTo("""{"string_field":"hello"}""")
+			}
+	}
+
+	@Test
+	fun serializeKebabCase() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.naming-strategy=kebab_case")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObject("hello")))
+					.isEqualTo("""{"string-field":"hello"}""")
+			}
+	}
+
+	@Test
+	fun serializePrettyPrint() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.pretty-print=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObject("hello")))
+					.isEqualTo(
+						"""
+						{
+						    "stringField": "hello"
+						}
+						""".trimIndent()
+					)
+			}
+	}
+
+	@Test
+	@Suppress("JsonStandardCompliance")
+	fun deserializeLenient() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.lenient=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObject>("""{"stringField":hello}"""))
+					.isEqualTo(DataObject("hello"))
+			}
+	}
+
+	@Test
+	fun deserializeIgnoreUnknownKeys() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.ignore-unknown-keys=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObject>("""{"stringField":"hello", "anotherField":"value"}"""))
+					.isEqualTo(DataObject("hello"))
+			}
+	}
+
+	@Test
+	fun serializeDefaults() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.encode-defaults=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObjectWithDefault("hello")))
+					.isEqualTo("""{"stringField":"hello","defaultField":"default"}""")
+			}
+	}
+
+	@Test
+	fun serializeExplicitNullsFalse() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.explicit-nulls=false")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObjectWithDefault(null, "hello")))
+					.isEqualTo("""{"defaultField":"hello"}""")
+			}
+	}
+
+	@Test
+	fun deserializeCoerceInputValues() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.coerce-input-values=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObjectWithDefault>("""{"stringField":"hello", "defaultField":null}"""))
+					.isEqualTo(DataObjectWithDefault("hello", "default"))
+			}
+	}
+
+	@Test
+	fun serializeStructuredMapKeys() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.allow-structured-map-keys=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				val map = mapOf(
+					DataObject("key1") to "value1",
+					DataObject("key2") to "value2",
+				)
+				assertThat(json.encodeToString(map))
+					.isEqualTo("""[{"stringField":"key1"},"value1",{"stringField":"key2"},"value2"]""")
+			}
+	}
+
+	@Test
+	fun serializeSpecialFloatingPointValues() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.allow-special-floating-point-values=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.encodeToString(DataObjectDouble(Double.NaN)))
+					.isEqualTo("""{"value":NaN}""")
+			}
+	}
+
+	@Test
+	fun serializeClassDiscriminator() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.class-discriminator=class")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				val value: BaseClass = ChildClass("value")
+				assertThat(json.encodeToString(value))
+					.isEqualTo("""{"class":"child","stringField":"value"}""")
+			}
+	}
+
+	@Test
+	fun serializeClassDiscriminatorNone() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.class-discriminator-mode=none")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				val value: BaseClass = ChildClass("value")
+				assertThat(json.encodeToString(value))
+					.isEqualTo("""{"stringField":"value"}""")
+			}
+	}
+
+	@Test
+	fun deserializeEnumsCaseInsensitive() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.decode-enums-case-insensitive=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObjectEnumValues>("""{"values":["value_A", "alternative"]}"""))
+					.isEqualTo(DataObjectEnumValues(listOf(EnumValue.VALUE_A, EnumValue.VALUE_B)))
+			}
+	}
+
+	@Test
+	fun deserializeAlternativeNames() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.use-alternative-names=false")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThatExceptionOfType(SerializationException::class.java).isThrownBy {
+					json.decodeFromString<DataObject>("""{"alternative":"hello"}""")
+				}.withMessageContaining("Encountered an unknown key")
+			}
+	}
+
+	@Test
+	@Suppress("JsonStandardCompliance")
+	fun deserializeTrailingComma() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.allow-trailing-comma=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObject>("""{"stringField":"hello",}"""))
+					.isEqualTo(DataObject("hello"))
+			}
+	}
+
+	@Test
+	@Suppress("JsonStandardCompliance")
+	fun deserializeComments() {
+		this.contextRunner
+			.withPropertyValues("spring.kotlin-serialization.allow-comments=true")
+			.run { context ->
+				val json = context.getBean(Json::class.java)
+				assertThat(json.decodeFromString<DataObject>("""{"stringField":"hello" /*comment*/}"""))
+					.isEqualTo(DataObject("hello"))
+			}
+	}
+
+	@Serializable
+	@OptIn(ExperimentalSerializationApi::class)
+	private data class DataObject(@JsonNames("alternative") private val stringField: String)
+
+	@Serializable
+	private data class DataObjectWithDefault(
+		private val stringField: String?,
+		private val defaultField: String = "default",
+	)
+
+	@Serializable
+	private data class DataObjectDouble(private val value: Double)
+
+	@OptIn(ExperimentalSerializationApi::class)
+	enum class EnumValue { VALUE_A, @JsonNames("Alternative") VALUE_B }
+
+	@Serializable
+	private data class DataObjectEnumValues(private val values: List<EnumValue>)
+
+	@Serializable
+	sealed class BaseClass {
+		abstract val stringField: String
+	}
+
+	@Serializable
+	@SerialName("child")
+	class ChildClass(override val stringField: String) : BaseClass()
+
+	@Configuration(proxyBeanMethods = false)
+	class CustomKotlinSerializationConfig {
+
+		@Bean
+		@OptIn(ExperimentalSerializationApi::class)
+		fun customKotlinSerializationJson(): Json {
+			return Json { namingStrategy = JsonNamingStrategy.SnakeCase }
+		}
+
+	}
+
+}

module/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.test.autoconfigure.json.AutoConfigureJson.imports

@@ -2,3 +2,4 @@
 optional:org.springframework.boot.gson.autoconfigure.GsonAutoConfiguration
 org.springframework.boot.jackson.autoconfigure.JacksonAutoConfiguration
 optional:org.springframework.boot.jsonb.autoconfigure.JsonbAutoConfiguration
+optional:org.springframework.boot.kotlin.serialization.autoconfigure.KotlinSerializationAutoConfiguration

platform/spring-boot-dependencies/build.gradle

@@ -2037,6 +2037,7 @@ bom {
 				"spring-boot-jpa",
 				"spring-boot-jsonb",
 				"spring-boot-kafka",
+				"spring-boot-kotlin-serialization",
 				"spring-boot-ldap",
 				"spring-boot-liquibase",
 				"spring-boot-loader",
@@ -2117,6 +2118,7 @@ bom {
 				"spring-boot-starter-json",
 				"spring-boot-starter-jsonb",
 				"spring-boot-starter-kafka",
+				"spring-boot-starter-kotlin-serialization",
 				"spring-boot-starter-ldap",
 				"spring-boot-starter-liquibase",
 				"spring-boot-starter-log4j2",

settings.gradle

@@ -29,6 +29,9 @@ pluginManagement {
 			if (requested.id.id == "org.jetbrains.kotlin.plugin.spring") {
 				useVersion "${kotlinVersion}"
 			}
+			if (requested.id.id == "org.jetbrains.kotlin.plugin.serialization") {
+				useVersion "${kotlinVersion}"
+			}
 		}
 	}
 	includeBuild("gradle/plugins")
@@ -123,6 +126,7 @@ include "module:spring-boot-jooq"
 include "module:spring-boot-jpa"
 include "module:spring-boot-jsonb"
 include "module:spring-boot-kafka"
+include "module:spring-boot-kotlin-serialization"
 include "module:spring-boot-ldap"
 include "module:spring-boot-liquibase"
 include "module:spring-boot-mail"
@@ -213,6 +217,7 @@ include "starter:spring-boot-starter-jooq"
 include "starter:spring-boot-starter-json"
 include "starter:spring-boot-starter-jsonb"
 include "starter:spring-boot-starter-kafka"
+include "starter:spring-boot-starter-kotlin-serialization"
 include "starter:spring-boot-starter-ldap"
 include "starter:spring-boot-starter-liquibase"
 include "starter:spring-boot-starter-log4j2"

starter/spring-boot-starter-kotlin-serialization/build.gradle

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2012-present 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
+ *
+ *      https://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.
+ */
+
+plugins {
+	id "org.springframework.boot.starter"
+}
+
+description = "Starter for Kotlin Serialization"
+
+dependencies {
+	api(project(":starter:spring-boot-starter"))
+
+	api(project(":module:spring-boot-kotlin-serialization"))
+}