Exclude Part and MultipartFile from nested constructor binding

Closes gh-31669

spring-context/src/main/java/org/springframework/validation/DataBinder.java

@@ -948,7 +948,7 @@ private Object createObject(ResolvableType objectType, String nestedPath, ValueR
 				Class<?> paramType = paramTypes[i];
 				Object value = valueResolver.resolveValue(paramPath, paramType);
 
-				if (value == null && shouldCreateObject(param)) {
+				if (value == null && shouldConstructArgument(param)) {
 					ResolvableType type = ResolvableType.forMethodParameter(param);
 					args[i] = createObject(type, paramPath + ".", valueResolver);
 				}
@@ -1008,7 +1008,14 @@ private Object createObject(ResolvableType objectType, String nestedPath, ValueR
 		return (isOptional && !nestedPath.isEmpty() ? Optional.ofNullable(result) : result);
 	}
 
-	private static boolean shouldCreateObject(MethodParameter param) {
+	/**
+	 * Whether to instantiate the constructor argument of the given type,
+	 * matching its own constructor arguments to bind values.
+	 * <p>By default, simple value types, maps, collections, and arrays are
+	 * excluded from nested constructor binding initialization.
+	 * @since 6.1.2
+	 */
+	protected boolean shouldConstructArgument(MethodParameter param) {
 		Class<?> type = param.nestedIfOptional().getNestedParameterType();
 		return !(BeanUtils.isSimpleValueType(type) ||
 				Collection.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type) || type.isArray());

spring-web/src/main/java/org/springframework/web/bind/ServletRequestDataBinder.java

@@ -24,6 +24,7 @@
 import jakarta.servlet.http.Part;
 
 import org.springframework.beans.MutablePropertyValues;
+import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
 import org.springframework.lang.Nullable;
@@ -120,6 +121,13 @@ protected ServletRequestValueResolver createValueResolver(ServletRequest request
 		return new ServletRequestValueResolver(request, this);
 	}
 
+	@Override
+	protected boolean shouldConstructArgument(MethodParameter param) {
+		Class<?> type = param.nestedIfOptional().getNestedParameterType();
+		return (super.shouldConstructArgument(param) &&
+				!MultipartFile.class.isAssignableFrom(type) && !Part.class.isAssignableFrom(type));
+	}
+
 	/**
 	 * Bind the parameters of the given request to this binder's target,
 	 * also binding multipart files in case of a multipart request.

spring-web/src/main/java/org/springframework/web/bind/support/WebRequestDataBinder.java

@@ -18,8 +18,10 @@
 
 import jakarta.servlet.ServletRequest;
 import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.Part;
 
 import org.springframework.beans.MutablePropertyValues;
+import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
@@ -30,6 +32,7 @@
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.context.request.WebRequest;
+import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.multipart.MultipartRequest;
 import org.springframework.web.multipart.support.StandardServletPartUtils;
 
@@ -118,6 +121,12 @@ public void construct(WebRequest request) {
 		}
 	}
 
+	@Override
+	protected boolean shouldConstructArgument(MethodParameter param) {
+		Class<?> type = param.nestedIfOptional().getNestedParameterType();
+		return (super.shouldConstructArgument(param) &&
+				!MultipartFile.class.isAssignableFrom(type) && !Part.class.isAssignableFrom(type));
+	}
 
 	/**
 	 * Bind the parameters of the given request to this binder's target,

spring-web/src/test/java/org/springframework/web/method/annotation/ModelAttributeMethodProcessorTests.java

@@ -29,6 +29,7 @@
 import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.SynthesizingMethodParameter;
 import org.springframework.format.support.DefaultFormattingConversionService;
+import org.springframework.lang.Nullable;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.Errors;
 import org.springframework.web.bind.MethodArgumentNotValidException;
@@ -41,6 +42,7 @@
 import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.context.request.WebRequest;
 import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 
 import static java.lang.annotation.ElementType.CONSTRUCTOR;
@@ -298,6 +300,7 @@ public void resolveConstructorListArgumentFromCommaSeparatedRequestParameter() t
 		Object resolved = this.processor.resolveArgument(this.beanWithConstructorArgs, this.container, requestWithParam, factory);
 		assertThat(resolved).isInstanceOf(TestBeanWithConstructorArgs.class);
 		assertThat(((TestBeanWithConstructorArgs) resolved).listOfStrings).containsExactly("1", "2");
+		assertThat(((TestBeanWithConstructorArgs) resolved).file).isNull();
 	}
 
 	private void testGetAttributeFromModel(String expectedAttrName, MethodParameter param) throws Exception {
@@ -375,8 +378,11 @@ static class TestBeanWithConstructorArgs {
 
 		final List<String> listOfStrings;
 
-		public TestBeanWithConstructorArgs(List<String> listOfStrings) {
+		final MultipartFile file;
+
+		public TestBeanWithConstructorArgs(List<String> listOfStrings, @Nullable MultipartFile file) {
 			this.listOfStrings = listOfStrings;
+			this.file = file;
 		}
 	}