Avoid nested constructor binding if there are no request parameters

Closes gh-31821

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

@@ -948,7 +948,7 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 				Class<?> paramType = paramTypes[i];
 				Object value = valueResolver.resolveValue(paramPath, paramType);
 
-				if (value == null && shouldConstructArgument(param)) {
+				if (value == null && shouldConstructArgument(param) && hasValuesFor(paramPath, valueResolver)) {
 					ResolvableType type = ResolvableType.forMethodParameter(param);
 					args[i] = createObject(type, paramPath + ".", valueResolver);
 				}
@@ -1022,6 +1022,15 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 				type.getPackageName().startsWith("java."));
 	}
 
+	private boolean hasValuesFor(String paramPath, ValueResolver resolver) {
+		for (String name : resolver.getNames()) {
+			if (name.startsWith(paramPath + ".")) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	private void validateConstructorArgument(
 			Class<?> constructorClass, String nestedPath, String name, @Nullable Object value) {
 
@@ -1293,7 +1302,6 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 	 * Strategy for {@link #construct constructor binding} to look up the values
 	 * to bind to a given constructor parameter.
 	 */
-	@FunctionalInterface
 	public interface ValueResolver {
 
 		/**
@@ -1305,6 +1313,13 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 		 */
 		@Nullable
 		Object resolveValue(String name, Class<?> type);
+
+		/**
+		 * Return the names of all property values.
+		 * @since 6.1.2
+		 */
+		Set<String> getNames();
+
 	}
 
 

spring-context/src/test/java/org/springframework/validation/DataBinderConstructTests.java

@@ -19,12 +19,14 @@ package org.springframework.validation;
 import java.beans.ConstructorProperties;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 
 import jakarta.validation.constraints.NotNull;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.ResolvableType;
 import org.springframework.format.support.DefaultFormattingConversionService;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -76,6 +78,17 @@ public class DataBinderConstructTests {
 		assertThat(bindingResult.getFieldValue("param3")).isNull();
 	}
 
+	@Test // gh-31821
+	void dataClassBindingWithNestedOptionalParameterWithMissingParameter() {
+		MapValueResolver valueResolver = new MapValueResolver(Map.of("param1", "value1"));
+		DataBinder binder = initDataBinder(NestedDataClass.class);
+		binder.construct(valueResolver);
+
+		NestedDataClass dataClass = getTarget(binder);
+		assertThat(dataClass.param1()).isEqualTo("value1");
+		assertThat(dataClass.nestedParam2()).isNull();
+	}
+
 	@Test
 	void dataClassBindingWithConversionError() {
 		MapValueResolver valueResolver = new MapValueResolver(Map.of("param1", "value1", "param2", "x"));
@@ -90,7 +103,7 @@ public class DataBinderConstructTests {
 	}
 
 	@SuppressWarnings("SameParameterValue")
-	private static DataBinder initDataBinder(Class<DataClass> targetType) {
+	private static DataBinder initDataBinder(Class<?> targetType) {
 		DataBinder binder = new DataBinder(null);
 		binder.setTargetType(ResolvableType.forClass(targetType));
 		binder.setConversionService(new DefaultFormattingConversionService());
@@ -137,17 +150,45 @@ public class DataBinderConstructTests {
 	}
 
 
+	private static class NestedDataClass {
+
+		private final String param1;
+
+		@Nullable
+		private final DataClass nestedParam2;
+
+		public NestedDataClass(String param1, @Nullable DataClass nestedParam2) {
+			this.param1 = param1;
+			this.nestedParam2 = nestedParam2;
+		}
+
+		public String param1() {
+			return this.param1;
+		}
+
+		@Nullable
+		public DataClass nestedParam2() {
+			return this.nestedParam2;
+		}
+	}
+
+
 	private static class MapValueResolver implements DataBinder.ValueResolver {
 
-		private final Map<String, Object> values;
+		private final Map<String, Object> map;
 
-		private MapValueResolver(Map<String, Object> values) {
-			this.values = values;
+		private MapValueResolver(Map<String, Object> map) {
+			this.map = map;
 		}
 
 		@Override
 		public Object resolveValue(String name, Class<?> type) {
-			return values.get(name);
+			return map.get(name);
+		}
+
+		@Override
+		public Set<String> getNames() {
+			return this.map.keySet();
 		}
 	}
 

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

@@ -17,7 +17,10 @@
 package org.springframework.web.bind;
 
 import java.lang.reflect.Array;
+import java.util.Enumeration;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 
 import jakarta.servlet.ServletRequest;
 import jakarta.servlet.http.HttpServletRequest;
@@ -213,6 +216,9 @@ public class ServletRequestDataBinder extends WebDataBinder {
 
 		private final WebDataBinder dataBinder;
 
+		@Nullable
+		private Set<String> parameterNames;
+
 		protected ServletRequestValueResolver(ServletRequest request, WebDataBinder dataBinder) {
 			this.request = request;
 			this.dataBinder = dataBinder;
@@ -261,6 +267,23 @@ public class ServletRequestDataBinder extends WebDataBinder {
 			}
 			return null;
 		}
+
+		@Override
+		public Set<String> getNames() {
+			if (this.parameterNames == null) {
+				this.parameterNames = initParameterNames(this.request);
+			}
+			return this.parameterNames;
+		}
+
+		protected Set<String> initParameterNames(ServletRequest request) {
+			Set<String> set = new LinkedHashSet<>();
+			Enumeration<String> enumeration = request.getParameterNames();
+			while (enumeration.hasMoreElements()) {
+				set.add(enumeration.nextElement());
+			}
+			return set;
+		}
 	}
 
 }

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

@@ -18,6 +18,7 @@ package org.springframework.web.bind.support;
 
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.TreeMap;
 
 import reactor.core.publisher.Mono;
@@ -164,6 +165,11 @@ public class WebExchangeDataBinder extends WebDataBinder {
 		public Object resolveValue(String name, Class<?> type) {
 			return this.map.get(name);
 		}
+
+		@Override
+		public Set<String> getNames() {
+			return this.map.keySet();
+		}
 	}
 
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ExtendedServletRequestDataBinder.java

@@ -17,6 +17,7 @@
 package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.util.Map;
+import java.util.Set;
 
 import jakarta.servlet.ServletRequest;
 
@@ -121,6 +122,16 @@ public class ExtendedServletRequestDataBinder extends ServletRequestDataBinder {
 			}
 			return value;
 		}
+
+		@Override
+		protected Set<String> initParameterNames(ServletRequest request) {
+			Set<String> set = super.initParameterNames(request);
+			Map<String, String> uriVars = getUriVars(getRequest());
+			if (uriVars != null) {
+				set.addAll(uriVars.keySet());
+			}
+			return set;
+		}
 	}
 
 }