Refine type conversion errors in ModelAttributeMethodProcessor

This commit turns TypeMismatchException thrown in
ModelAttributeMethodArgumentResolver#createAttribute into
proper ServerWebInputException in order get HTTP response
with 400 Bad Request status code instead of 500 Internal error.

Closes gh-31045

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolverTests.java

@@ -38,6 +38,7 @@ import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
 import org.springframework.web.bind.support.WebExchangeBindException;
 import org.springframework.web.reactive.BindingContext;
 import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.ServerWebInputException;
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest;
 import org.springframework.web.testfixture.method.ResolvableMethod;
 import org.springframework.web.testfixture.server.MockServerWebExchange;
@@ -50,6 +51,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Rossen Stoyanchev
  * @author Juergen Hoeller
  * @author Sam Brannen
+ * @author Sebastien Deleuze
  */
 class ModelAttributeMethodArgumentResolverTests {
 
@@ -388,6 +390,16 @@ class ModelAttributeMethodArgumentResolverTests {
 		assertThat(model.get(bindingResultKey)).isInstanceOf(BindingResult.class);
 	}
 
+	@Test
+	void bindDataClassError() {
+		MethodParameter parameter = this.testMethod.annotNotPresent(ModelAttribute.class).arg(DataClass.class);
+		Mono<Object> mono = createResolver().resolveArgument(parameter, this.bindContext, postForm("name=Robert&age=invalid&count=1"));
+		StepVerifier.create(mono)
+				.expectNextCount(0)
+				.expectError(ServerWebInputException.class)
+				.verify();
+	}
+
 	// TODO: SPR-15871, SPR-15542
 
 

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

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2002-2023 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.web.reactive.result.method.annotation
+
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import org.springframework.core.MethodParameter
+import org.springframework.core.ReactiveAdapterRegistry
+import org.springframework.http.MediaType
+import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean
+import org.springframework.web.bind.annotation.ModelAttribute
+import org.springframework.web.bind.support.ConfigurableWebBindingInitializer
+import org.springframework.web.reactive.BindingContext
+import org.springframework.web.server.ServerWebExchange
+import org.springframework.web.server.ServerWebInputException
+import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest
+import org.springframework.web.testfixture.method.ResolvableMethod
+import org.springframework.web.testfixture.server.MockServerWebExchange
+import reactor.core.publisher.Mono
+import reactor.test.StepVerifier
+
+/**
+ * Kotlin test fixture for [ModelAttributeMethodArgumentResolver].
+ *
+ * @author Sebastien Deleuze
+ */
+class ModelAttributeMethodArgumentResolverKotlinTests {
+
+	private val testMethod = ResolvableMethod.on(javaClass).named("handle").build()
+
+	private lateinit var bindContext: BindingContext
+
+	@BeforeEach
+	fun setup() {
+		val validator = LocalValidatorFactoryBean()
+		validator.afterPropertiesSet()
+		val initializer = ConfigurableWebBindingInitializer()
+		initializer.validator = validator
+		this.bindContext = BindingContext(initializer)
+	}
+
+	@Test
+	fun bindDataClassError() {
+		val parameter: MethodParameter = this.testMethod.annotNotPresent(ModelAttribute::class.java).arg(DataClass::class.java)
+		val mono: Mono<Any> =
+			createResolver().resolveArgument(parameter, this.bindContext, postForm("name=Robert&age=invalid&count=1"))
+		StepVerifier.create(mono)
+			.expectNextCount(0)
+			.expectError(ServerWebInputException::class.java)
+			.verify()
+	}
+
+	private fun createResolver(): ModelAttributeMethodArgumentResolver {
+		return ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance(), false)
+	}
+
+	private fun postForm(formData: String): ServerWebExchange {
+		return MockServerWebExchange.from(
+			MockServerHttpRequest.post("/")
+				.contentType(MediaType.APPLICATION_FORM_URLENCODED)
+				.body(formData)
+		)
+	}
+
+	@Suppress("UNUSED_PARAMETER")
+	private fun handle(dataClassNotAnnotated: DataClass) {
+	}
+
+	private class DataClass(val name: String, val age: Int, val count: Int)
+
+}