Support nullable Kotlin value class arguments

This commit refines WebMVC and WebFlux argument resolution in order to
convert properly Kotlin value class arguments by using the type of the
value instead of the type of the value class.

Closes gh-32353

spring-web/src/main/java/org/springframework/web/method/annotation/AbstractNamedValueMethodArgumentResolver.java

@@ -26,6 +26,7 @@ import kotlin.reflect.KFunction;
 import kotlin.reflect.KParameter;
 import kotlin.reflect.jvm.ReflectJvmMapping;
 
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.ConversionNotSupportedException;
 import org.springframework.beans.TypeMismatchException;
 import org.springframework.beans.factory.config.BeanExpressionContext;
@@ -281,8 +282,12 @@ public abstract class AbstractNamedValueMethodArgumentResolver implements Handle
 			NamedValueInfo namedValueInfo, @Nullable Object arg) throws Exception {
 
 		WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
+		Class<?> parameterType = parameter.getParameterType();
+		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isInlineClass(parameterType)) {
+			parameterType = BeanUtils.findPrimaryConstructor(parameterType).getParameterTypes()[0];
+		}
 		try {
-			arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);
+			arg = binder.convertIfNecessary(arg, parameterType, parameter);
 		}
 		catch (ConversionNotSupportedException ex) {
 			throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(),

spring-web/src/test/kotlin/org/springframework/web/method/annotation/RequestParamMethodArgumentResolverKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -25,7 +25,6 @@ import org.springframework.core.annotation.SynthesizingMethodParameter
 import org.springframework.core.convert.support.DefaultConversionService
 import org.springframework.http.HttpMethod
 import org.springframework.http.MediaType
-import org.springframework.util.ReflectionUtils
 import org.springframework.web.bind.MissingServletRequestParameterException
 import org.springframework.web.bind.annotation.RequestParam
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer
@@ -39,6 +38,7 @@ import org.springframework.web.testfixture.servlet.MockHttpServletRequest
 import org.springframework.web.testfixture.servlet.MockHttpServletResponse
 import org.springframework.web.testfixture.servlet.MockMultipartFile
 import org.springframework.web.testfixture.servlet.MockMultipartHttpServletRequest
+import kotlin.reflect.jvm.javaMethod
 
 /**
  * Kotlin test fixture for [RequestParamMethodArgumentResolver].
@@ -70,6 +70,9 @@ class RequestParamMethodArgumentResolverKotlinTests {
 	lateinit var nonNullableMultipartParamRequired: MethodParameter
 	lateinit var nonNullableMultipartParamNotRequired: MethodParameter
 
+	lateinit var nonNullableValueClassParam: MethodParameter
+	lateinit var nullableValueClassParam: MethodParameter
+
 
 	@BeforeEach
 	fun setup() {
@@ -80,10 +83,8 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		binderFactory = DefaultDataBinderFactory(initializer)
 		webRequest = ServletWebRequest(request, MockHttpServletResponse())
 
-		val method = ReflectionUtils.findMethod(javaClass, "handle",
-			String::class.java, String::class.java, String::class.java, String::class.java,
-			Boolean::class.java, Boolean::class.java, Int::class.java, Int::class.java, String::class.java, String::class.java,
-			MultipartFile::class.java, MultipartFile::class.java, MultipartFile::class.java, MultipartFile::class.java)!!
+		val method = RequestParamMethodArgumentResolverKotlinTests::handle.javaMethod!!
+		val valueClassMethod = RequestParamMethodArgumentResolverKotlinTests::handleValueClass.javaMethod!!
 
 		nullableParamRequired = SynthesizingMethodParameter(method, 0)
 		nullableParamNotRequired = SynthesizingMethodParameter(method, 1)
@@ -101,6 +102,9 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		nullableMultipartParamNotRequired = SynthesizingMethodParameter(method, 11)
 		nonNullableMultipartParamRequired = SynthesizingMethodParameter(method, 12)
 		nonNullableMultipartParamNotRequired = SynthesizingMethodParameter(method, 13)
+
+		nonNullableValueClassParam = SynthesizingMethodParameter(valueClassMethod, 0)
+		nullableValueClassParam = SynthesizingMethodParameter(valueClassMethod, 1)
 	}
 
 	@Test
@@ -317,6 +321,20 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		}
 	}
 
+	@Test
+	fun resolveNonNullableValueClass() {
+		request.addParameter("value", "123")
+		var result = resolver.resolveArgument(nonNullableValueClassParam, null, webRequest, binderFactory)
+		assertThat(result).isEqualTo(123)
+	}
+
+	@Test
+	fun resolveNullableValueClass() {
+		request.addParameter("value", "123")
+		var result = resolver.resolveArgument(nullableValueClassParam, null, webRequest, binderFactory)
+		assertThat(result).isEqualTo(123)
+	}
+
 
 	@Suppress("unused_parameter")
 	fun handle(
@@ -338,5 +356,13 @@ class RequestParamMethodArgumentResolverKotlinTests {
 			@RequestParam("mfile", required = false) nonNullableMultipartParamNotRequired: MultipartFile) {
 	}
 
+	@Suppress("unused_parameter")
+	fun handleValueClass(
+		@RequestParam("value") nonNullable: ValueClass,
+		@RequestParam("value") nullable: ValueClass?) {
+	}
+
+	@JvmInline value class ValueClass(val value: Int)
+
 }
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/AbstractNamedValueArgumentResolver.java

@@ -26,6 +26,7 @@ import kotlin.reflect.KParameter;
 import kotlin.reflect.jvm.ReflectJvmMapping;
 import reactor.core.publisher.Mono;
 
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.ConversionNotSupportedException;
 import org.springframework.beans.TypeMismatchException;
 import org.springframework.beans.factory.config.BeanExpressionContext;
@@ -197,8 +198,12 @@ public abstract class AbstractNamedValueArgumentResolver extends HandlerMethodAr
 			BindingContext bindingContext, ServerWebExchange exchange) {
 
 		WebDataBinder binder = bindingContext.createDataBinder(exchange, namedValueInfo.name);
+		Class<?> parameterType = parameter.getParameterType();
+		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isInlineClass(parameterType)) {
+			parameterType = BeanUtils.findPrimaryConstructor(parameterType).getParameterTypes()[0];
+		}
 		try {
-			value = binder.convertIfNecessary(value, parameter.getParameterType(), parameter);
+			value = binder.convertIfNecessary(value, parameterType, parameter);
 		}
 		catch (ConversionNotSupportedException ex) {
 			throw new ServerErrorException("Conversion not supported.", parameter, ex);

spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/method/annotation/RequestParamMethodArgumentResolverKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -22,14 +22,14 @@ import org.springframework.core.MethodParameter
 import org.springframework.core.ReactiveAdapterRegistry
 import org.springframework.core.annotation.SynthesizingMethodParameter
 import org.springframework.format.support.DefaultFormattingConversionService
-import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest
-import org.springframework.web.testfixture.server.MockServerWebExchange
-import org.springframework.util.ReflectionUtils
 import org.springframework.web.bind.annotation.RequestParam
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer
 import org.springframework.web.reactive.BindingContext
 import org.springframework.web.server.ServerWebInputException
+import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest
+import org.springframework.web.testfixture.server.MockServerWebExchange
 import reactor.test.StepVerifier
+import kotlin.reflect.jvm.javaMethod
 
 /**
  * Kotlin test fixture for [RequestParamMethodArgumentResolver].
@@ -53,6 +53,9 @@ class RequestParamMethodArgumentResolverKotlinTests {
 	lateinit var defaultValueStringParamRequired: MethodParameter
 	lateinit var defaultValueStringParamNotRequired: MethodParameter
 
+	lateinit var nonNullableValueClassParam: MethodParameter
+	lateinit var nullableValueClassParam: MethodParameter
+
 
 	@BeforeEach
 	fun setup() {
@@ -61,10 +64,8 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		initializer.conversionService = DefaultFormattingConversionService()
 		bindingContext = BindingContext(initializer)
 
-		val method = ReflectionUtils.findMethod(javaClass, "handle",
-			String::class.java, String::class.java, String::class.java, String::class.java,
-			Boolean::class.java, Boolean::class.java, Int::class.java, Int::class.java,
-			String::class.java, String::class.java)!!
+		val method = RequestParamMethodArgumentResolverKotlinTests::handle.javaMethod!!
+		val valueClassMethod = RequestParamMethodArgumentResolverKotlinTests::handleValueClass.javaMethod!!
 
 		nullableParamRequired = SynthesizingMethodParameter(method, 0)
 		nullableParamNotRequired = SynthesizingMethodParameter(method, 1)
@@ -77,6 +78,9 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		defaultValueIntParamNotRequired = SynthesizingMethodParameter(method, 7)
 		defaultValueStringParamRequired = SynthesizingMethodParameter(method, 8)
 		defaultValueStringParamNotRequired = SynthesizingMethodParameter(method, 9)
+
+		nonNullableValueClassParam = SynthesizingMethodParameter(valueClassMethod, 0)
+		nullableValueClassParam = SynthesizingMethodParameter(valueClassMethod, 1)
 	}
 
 	@Test
@@ -219,6 +223,20 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		StepVerifier.create(result).expectComplete().verify()
 	}
 
+	@Test
+	fun resolveNonNullableValueClass() {
+		var exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/path?value=123"))
+		var result = resolver.resolveArgument(nonNullableValueClassParam, bindingContext, exchange)
+		StepVerifier.create(result).expectNext(123).expectComplete().verify()
+	}
+
+	@Test
+	fun resolveNullableValueClass() {
+		var exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/path?value=123"))
+		var result = resolver.resolveArgument(nullableValueClassParam, bindingContext, exchange)
+		StepVerifier.create(result).expectNext(123).expectComplete().verify()
+	}
+
 
 	@Suppress("unused_parameter")
 	fun handle(
@@ -235,5 +253,13 @@ class RequestParamMethodArgumentResolverKotlinTests {
 			@RequestParam("value", required = false) withDefaultValueStringParamNotRequired: String = "default") {
 	}
 
+	@Suppress("unused_parameter")
+	fun handleValueClass(
+		@RequestParam("value") nonNullable: ValueClass,
+		@RequestParam("value") nullable: ValueClass?) {
+	}
+
+	@JvmInline value class ValueClass(val value: Int)
+
 }