Improve method validation support for errors on elements within a container

spring-context/src/main/java/org/springframework/validation/beanvalidation/MethodValidationAdapter.java

@@ -302,7 +302,7 @@ private MethodValidationResult adaptViolations(
 			Function<Integer, Object> argumentFunction) {
 
 		Map<MethodParameter, ValueResultBuilder> parameterViolations = new LinkedHashMap<>();
-		Map<Path.Node, BeanResultBuilder> cascadedViolations = new LinkedHashMap<>();
+		Map<CascadedViolationsKey, BeanResultBuilder> cascadedViolations = new LinkedHashMap<>();
 
 		for (ConstraintViolation<Object> violation : violations) {
 			Iterator<Path.Node> itr = violation.getPropertyPath().iterator();
@@ -329,7 +329,8 @@ else if (node.getKind().equals(ElementKind.RETURN_VALUE)) {
 				}
 				else {
 					cascadedViolations
-							.computeIfAbsent(node, n -> new BeanResultBuilder(parameter, argument, itr.next()))
+							.computeIfAbsent(new CascadedViolationsKey(node, violation.getLeafBean()),
+											n -> new BeanResultBuilder(parameter, argument, itr.next(), violation.getLeafBean()))
 							.addViolation(violation);
 				}
 				break;
@@ -338,7 +339,7 @@ else if (node.getKind().equals(ElementKind.RETURN_VALUE)) {
 
 		List<ParameterValidationResult> validatonResultList = new ArrayList<>();
 		parameterViolations.forEach((parameter, builder) -> validatonResultList.add(builder.build()));
-		cascadedViolations.forEach((node, builder) -> validatonResultList.add(builder.build()));
+		cascadedViolations.forEach((violationsKey, builder) -> validatonResultList.add(builder.build()));
 		validatonResultList.sort(resultComparator);
 
 		return MethodValidationResult.create(target, method, validatonResultList);
@@ -372,6 +373,14 @@ private BindingResult createBindingResult(MethodParameter parameter, @Nullable O
 		return result;
 	}
 
+	/**
+	 * A unique key for the cascaded violations map. Individually, the node and leaf bean may not be unique for all
+	 * collection types ({@link Set} will have the same node and {@link List} may have the same leaf), but together
+	 * they should represent a distinct pairing.
+	 * @param node the path of the violation
+	 * @param leafBean the validated object
+	 */
+	record CascadedViolationsKey(Path.Node node, Object leafBean) { }
 
 	/**
 	 * Strategy to resolve the name of an {@code @Valid} method parameter to
@@ -446,25 +455,20 @@ private final class BeanResultBuilder {
 
 		private final Set<ConstraintViolation<Object>> violations = new LinkedHashSet<>();
 
-		public BeanResultBuilder(MethodParameter parameter, @Nullable Object argument, Path.Node node) {
+		public BeanResultBuilder(MethodParameter parameter, @Nullable Object argument, Path.Node node, @Nullable Object leafBean) {
 			this.parameter = parameter;
 
 			this.containerIndex = node.getIndex();
 			this.containerKey = node.getKey();
-			if (argument instanceof List<?> list && this.containerIndex != null) {
-				this.container = list;
-				argument = list.get(this.containerIndex);
-			}
-			else if (argument instanceof Map<?, ?> map && this.containerKey != null) {
-				this.container = map;
-				argument = map.get(this.containerKey);
+			if (argument != null && !argument.equals(leafBean)) {
+				this.container = argument;
 			}
 			else {
 				this.container = null;
 			}
 
-			this.argument = argument;
-			this.errors = createBindingResult(parameter, argument);
+			this.argument = leafBean;
+			this.errors = createBindingResult(parameter, leafBean);
 		}
 
 		public void addViolation(ConstraintViolation<Object> violation) {

spring-context/src/main/java/org/springframework/validation/method/ParameterErrors.java

@@ -32,11 +32,10 @@
  * {@link Errors#getAllErrors()}, but this subclass provides access to the same
  * as {@link FieldError}s.
  *
- * <p>When the method parameter is a {@link List} or {@link java.util.Map},
- * a separate {@link ParameterErrors} is created for each list or map value for
- * which there are validation errors. In such cases, the {@link #getContainer()}
- * method returns the list or map, while {@link #getContainerIndex()}
- * and {@link #getContainerKey()} return the value index or key.
+ * <p>When the method parameter is a multi-element container like {@link List} or
+ * {@link java.util.Map}, a separate {@link ParameterErrors} is created for each
+ * value for which there are validation errors. Otherwise, only a single
+ * {@link ParameterErrors} will be created.
  *
  * @author Rossen Stoyanchev
  * @since 6.1
@@ -71,30 +70,32 @@ public ParameterErrors(
 
 
 	/**
-	 * When {@code @Valid} is declared on a {@link List} or {@link java.util.Map}
-	 * method parameter, this method returns the list or map that contained the
-	 * validated object {@link #getArgument() argument}, while
-	 * {@link #getContainerIndex()} and {@link #getContainerKey()} returns the
-	 * respective index or key.
+	 * When {@code @Valid} is declared on a container type method parameter such as
+	 * {@link java.util.Collection}, {@link java.util.Optional} or {@link java.util.Map},
+	 * this method returns the parent that contained the validated object
+	 * {@link #getArgument() argument}, while {@link #getContainerIndex()} and
+	 * {@link #getContainerKey()} returns the respective index or key if the parameter's
+	 * datatype supports such access.
 	 */
 	@Nullable
 	public Object getContainer() {
 		return this.container;
 	}
 
 	/**
-	 * When {@code @Valid} is declared on a {@link List}, this method returns
-	 * the index under which the validated object {@link #getArgument() argument}
-	 * is stored in the list {@link #getContainer() container}.
+	 * When {@code @Valid} is declared on an indexed type, such as {@link List},
+	 * this method returns the index under which the validated object
+	 * {@link #getArgument() argument} is stored in the list
+	 * {@link #getContainer() container}.
 	 */
 	@Nullable
 	public Integer getContainerIndex() {
 		return this.containerIndex;
 	}
 
 	/**
-	 * When {@code @Valid} is declared on a {@link java.util.Map}, this method
-	 * returns the key under which the validated object {@link #getArgument()
+	 * When {@code @Valid} is declared on a keyed typed, such as {@link java.util.Map},
+	 * this method returns the key under which the validated object {@link #getArgument()
 	 * argument} is stored in the map {@link #getContainer()}.
 	 */
 	@Nullable

spring-context/src/test/java/org/springframework/validation/beanvalidation/MethodValidationAdapterTests.java

@@ -17,13 +17,16 @@
 package org.springframework.validation.beanvalidation;
 
 import java.lang.reflect.Method;
+import java.util.Collection;
 import java.util.List;
 import java.util.Locale;
+import java.util.Set;
 import java.util.function.Consumer;
 
 import jakarta.validation.Valid;
 import jakarta.validation.constraints.Max;
 import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.Size;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -47,9 +50,9 @@
  */
 public class MethodValidationAdapterTests {
 
-	private static final Person faustino1234 = new Person("Faustino1234");
+	private static final Person faustino1234 = new Person("Faustino1234", List.of("Working on Spring"));
 
-	private static final Person cayetana6789 = new Person("Cayetana6789");
+	private static final Person cayetana6789 = new Person("Cayetana6789", List.of("  "));
 
 
 	private final MethodValidationAdapter validationAdapter = new MethodValidationAdapter();
@@ -88,7 +91,13 @@ void validateArguments() {
 				codes [Size.guardian.name,Size.name,Size.java.lang.String,Size]; \
 				arguments [org.springframework.context.support.DefaultMessageSourceResolvable: \
 				codes [guardian.name,name]; arguments []; default message [name],10,1]; \
-				default message [size must be between 1 and 10]"""));
+				default message [size must be between 1 and 10]""", """
+				Field error in object 'guardian' on field 'hobbies[0]': rejected value [  ]; \
+				codes [NotBlank.guardian.hobbies[0],NotBlank.guardian.hobbies,NotBlank.hobbies[0],\
+				NotBlank.hobbies,NotBlank.java.lang.String,NotBlank]; arguments \
+				[org.springframework.context.support.DefaultMessageSourceResolvable: codes \
+				[guardian.hobbies[0],hobbies[0]]; arguments []; default message [hobbies[0]]]; \
+				default message [must not be blank]"""));
 
 			assertValueResult(ex.getValueResults().get(0), 2, 3, List.of("""
 				org.springframework.context.support.DefaultMessageSourceResolvable: \
@@ -106,7 +115,7 @@ void validateArgumentWithCustomObjectName() {
 
 		this.validationAdapter.setObjectNameResolver((param, value) -> "studentToAdd");
 
-		testArgs(target, method, new Object[] {faustino1234, new Person("Joe"), 1}, ex -> {
+		testArgs(target, method, new Object[] {faustino1234, new Person("Joe", List.of()), 1}, ex -> {
 
 			assertThat(ex.getAllValidationResults()).hasSize(1);
 
@@ -178,7 +187,49 @@ void validateListArgument() {
 				codes [Size.people.name,Size.name,Size.java.lang.String,Size]; \
 				arguments [org.springframework.context.support.DefaultMessageSourceResolvable: \
 				codes [people.name,name]; arguments []; default message [name],10,1]; \
-				default message [size must be between 1 and 10]"""));
+				default message [size must be between 1 and 10]""", """
+				Field error in object 'people' on field 'hobbies[0]': rejected value [  ]; \
+				codes [NotBlank.people.hobbies[0],NotBlank.people.hobbies,NotBlank.hobbies[0],\
+				NotBlank.hobbies,NotBlank.java.lang.String,NotBlank]; arguments \
+				[org.springframework.context.support.DefaultMessageSourceResolvable: codes \
+				[people.hobbies[0],hobbies[0]]; arguments []; default message [hobbies[0]]]; \
+				default message [must not be blank]"""));
+		});
+	}
+
+	@Test
+	void validateSetArgument() {
+		MyService target = new MyService();
+		Method method = getMethod(target, "addPeople");
+
+		testArgs(target, method, new Object[] {Set.of(faustino1234, cayetana6789)}, ex -> {
+
+			assertThat(ex.getAllValidationResults()).hasSize(2);
+
+			int paramIndex = 0;
+			String objectName = "people";
+			List<ParameterErrors> results = ex.getBeanResults();
+
+			assertThat(results).satisfiesExactlyInAnyOrder(
+				result -> assertBeanResult(result, paramIndex, objectName, faustino1234, List.of("""
+					Field error in object 'people' on field 'name': rejected value [Faustino1234]; \
+					codes [Size.people.name,Size.name,Size.java.lang.String,Size]; \
+					arguments [org.springframework.context.support.DefaultMessageSourceResolvable: \
+					codes [people.name,name]; arguments []; default message [name],10,1]; \
+					default message [size must be between 1 and 10]""")),
+				result -> assertBeanResult(result, paramIndex, objectName, cayetana6789, List.of("""
+					Field error in object 'people' on field 'name': rejected value [Cayetana6789]; \
+					codes [Size.people.name,Size.name,Size.java.lang.String,Size]; \
+					arguments [org.springframework.context.support.DefaultMessageSourceResolvable: \
+					codes [people.name,name]; arguments []; default message [name],10,1]; \
+					default message [size must be between 1 and 10]""", """
+					Field error in object 'people' on field 'hobbies[0]': rejected value [  ]; \
+					codes [NotBlank.people.hobbies[0],NotBlank.people.hobbies,NotBlank.hobbies[0],\
+					NotBlank.hobbies,NotBlank.java.lang.String,NotBlank]; arguments \
+					[org.springframework.context.support.DefaultMessageSourceResolvable: codes \
+					[people.hobbies[0],hobbies[0]]; arguments []; default message [hobbies[0]]]; \
+					default message [must not be blank]"""))
+			);
 		});
 	}
 
@@ -191,7 +242,7 @@ private void testReturnValue(Object target, Method method, @Nullable Object valu
 	}
 
 	private static void assertBeanResult(
-			ParameterErrors errors, int parameterIndex, String objectName, Object argument,
+			ParameterErrors errors, int parameterIndex, String objectName, @Nullable Object argument,
 			List<String> fieldErrors) {
 
 		assertThat(errors.getMethodParameter().getParameterIndex()).isEqualTo(parameterIndex);
@@ -234,14 +285,14 @@ public Person getPerson() {
 			throw new UnsupportedOperationException();
 		}
 
-		public void addPeople(@Valid List<Person> people) {
+		public void addPeople(@Valid Collection<Person> people) {
 		}
 
 	}
 
 
 	@SuppressWarnings("unused")
-	private record Person(@Size(min = 1, max = 10) String name) {
+	private record Person(@Size(min = 1, max = 10) String name, List<@NotBlank String> hobbies) {
 	}
 
 }