Introduce Kotlin Serialization auto-configuration

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

@@ -118,6 +118,7 @@ private void mailPrefixes(Config config) {
 	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
 - 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

@@ -157,6 +157,9 @@ 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.fasterxml.jackson.dataformat:jackson-dataformat-xml")
 	optional("com.google.code.gson:gson")
 	optional("jakarta.json.bind:jakarta.json.bind-api")

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

@@ -91,6 +91,12 @@ static class JsonbPreferred {
 
 		}
 
+		@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 @@
  * @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.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;
@@ -65,10 +66,33 @@ static class JsonbPreferred {
 
 		}
 
+		@Conditional(JacksonAndGsonAndKotlinSerializationMissingCondition.class)
+		static class JacksonAndGsonAndKotlinSerializationMissing {
+
+		}
+
+	}
+
+	private static class JacksonAndGsonAndKotlinSerializationMissingCondition extends NoneNestedConditions {
+
+		JacksonAndGsonAndKotlinSerializationMissingCondition() {
+			super(ConfigurationPhase.REGISTER_BEAN);
+		}
+
 		@SuppressWarnings("removal")
-		@ConditionalOnMissingBean({ org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.class,
-				GsonHttpMessageConverter.class })
-		static class JacksonAndGsonMissing {
+		@ConditionalOnBean(org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.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

@@ -22,6 +22,7 @@
 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 org.springframework.beans.factory.config.BeanDefinition;
@@ -44,6 +45,7 @@
 import org.springframework.http.converter.json.GsonHttpMessageConverter;
 import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 import org.springframework.http.converter.json.JsonbHttpMessageConverter;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
 
@@ -60,6 +62,7 @@
  * @author Eddú Meléndez
  * @author Moritz Halbritter
  * @author Sebastien Deleuze
+ * @author Dmitry Sulman
  */
 @SuppressWarnings("removal")
 class HttpMessageConvertersAutoConfigurationTests {
@@ -128,6 +131,7 @@ void gsonCanBePreferred() {
 			assertConverterBeanExists(context, GsonHttpMessageConverter.class, "gsonHttpMessageConverter");
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, GsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(MappingJackson2HttpMessageConverter.class);
 		});
 	}
@@ -159,10 +163,41 @@ void jsonbCanBePreferred() {
 			assertConverterBeanExists(context, JsonbHttpMessageConverter.class, "jsonbHttpMessageConverter");
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, JsonbHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(GsonHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(MappingJackson2HttpMessageConverter.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(MappingJackson2HttpMessageConverter.class);
+			});
+	}
+
 	@Test
 	void stringDefaultConverter() {
 		this.contextRunner.run(assertConverter(StringHttpMessageConverter.class, "stringHttpMessageConverter"));
@@ -206,6 +241,7 @@ void jacksonIsPreferredByDefault() {
 			assertConverterBeanRegisteredWithHttpMessageConverters(context, MappingJackson2HttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(GsonHttpMessageConverter.class);
 			assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+			assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 		});
 	}
 
@@ -216,6 +252,7 @@ void gsonIsPreferredIfJacksonIsNotAvailable() {
 				assertConverterBeanExists(context, GsonHttpMessageConverter.class, "gsonHttpMessageConverter");
 				assertConverterBeanRegisteredWithHttpMessageConverters(context, GsonHttpMessageConverter.class);
 				assertThat(context).doesNotHaveBean(JsonbHttpMessageConverter.class);
+				assertThat(context).doesNotHaveBean(KotlinSerializationJsonHttpMessageConverter.class);
 			});
 	}
 
@@ -267,7 +304,8 @@ void whenEncodingCharsetIsConfiguredThenStringMessageConverterUsesSpecificCharse
 	private ApplicationContextRunner allOptionsRunner() {
 		return this.contextRunner.withBean(Gson.class)
 			.withBean(ObjectMapper.class)
-			.withBean(Jsonb.class, JsonbBuilder::create);
+			.withBean(Jsonb.class, JsonbBuilder::create)
+			.withBean(Json.class, () -> Json.Default);
 	}
 
 	private ContextConsumer<AssertableApplicationContext> assertConverter(
@@ -351,6 +389,16 @@ JsonbHttpMessageConverter customJsonbMessageConverter(Jsonb jsonb) {
 
 	}
 
+	@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

@@ -30,6 +30,7 @@
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter;
 import org.springframework.http.converter.json.GsonHttpMessageConverter;
+import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
 import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
@@ -89,6 +90,25 @@ void addBeforeExistingEquivalentConverter() {
 				MappingJackson2HttpMessageConverter.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,
+				MappingJackson2HttpMessageConverter.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, MappingJackson2HttpMessageConverter.class);
+	}
+
 	@Test
 	void addNewConverters() {
 		HttpMessageConverter<?> converter1 = mock(HttpMessageConverter.class);