Reactive support in MethodValidationInterceptor

Closes gh-20781

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

@@ -140,6 +140,13 @@ public class MethodValidationAdapter implements MethodValidator {
 	}
 
 
+	/**
+	 * Return the {@link SpringValidatorAdapter} configured for use.
+	 */
+	public Supplier<SpringValidatorAdapter> getSpringValidatorAdapter() {
+		return this.validatorAdapter;
+	}
+
 	/**
 	 * Set the strategy to use to determine message codes for violations.
 	 * <p>Default is a DefaultMessageCodesResolver.

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

@@ -17,25 +17,39 @@
 package org.springframework.validation.beanvalidation;
 
 import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
+import java.util.Collections;
+import java.util.List;
 import java.util.Set;
 import java.util.function.Supplier;
 
 import jakarta.validation.ConstraintViolation;
 import jakarta.validation.ConstraintViolationException;
+import jakarta.validation.Valid;
 import jakarta.validation.Validator;
 import jakarta.validation.ValidatorFactory;
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
 
 import org.springframework.aop.ProxyMethodInvocation;
 import org.springframework.beans.factory.FactoryBean;
 import org.springframework.beans.factory.SmartFactoryBean;
+import org.springframework.core.MethodParameter;
+import org.springframework.core.ReactiveAdapter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.validation.BeanPropertyBindingResult;
+import org.springframework.validation.Errors;
 import org.springframework.validation.annotation.Validated;
 import org.springframework.validation.method.MethodValidationException;
 import org.springframework.validation.method.MethodValidationResult;
+import org.springframework.validation.method.ParameterErrors;
+import org.springframework.validation.method.ParameterValidationResult;
 
 /**
  * An AOP Alliance {@link MethodInterceptor} implementation that delegates to a
@@ -65,6 +79,10 @@ import org.springframework.validation.method.MethodValidationResult;
  */
 public class MethodValidationInterceptor implements MethodInterceptor {
 
+	private static final boolean REACTOR_PRESENT =
+			ClassUtils.isPresent("reactor.core.publisher.Mono", MethodValidationInterceptor.class.getClassLoader());
+
+
 	private final MethodValidationAdapter validationAdapter;
 
 	private final boolean adaptViolations;
@@ -135,6 +153,12 @@ public class MethodValidationInterceptor implements MethodInterceptor {
 		Object[] arguments = invocation.getArguments();
 		Class<?>[] groups = determineValidationGroups(invocation);
 
+		if (REACTOR_PRESENT) {
+			arguments = ReactorValidationHelper.insertAsyncValidation(
+					this.validationAdapter.getSpringValidatorAdapter(), this.adaptViolations,
+					target, method, arguments);
+		}
+
 		Set<ConstraintViolation<Object>> violations;
 
 		if (this.adaptViolations) {
@@ -206,4 +230,78 @@ public class MethodValidationInterceptor implements MethodInterceptor {
 		return this.validationAdapter.determineValidationGroups(target, invocation.getMethod());
 	}
 
+
+	/**
+	 * Helper class to decorate reactive arguments with async validation.
+	 */
+	private final static class ReactorValidationHelper {
+
+		private static final ReactiveAdapterRegistry reactiveAdapterRegistry =
+				ReactiveAdapterRegistry.getSharedInstance();
+
+
+		public static Object[] insertAsyncValidation(
+				Supplier<SpringValidatorAdapter> validatorAdapterSupplier, boolean adaptViolations,
+				Object target, Method method, Object[] arguments) {
+
+			for (int i = 0; i < method.getParameterCount(); i++) {
+				if (arguments[i] == null) {
+					continue;
+				}
+				Class<?> parameterType = method.getParameterTypes()[i];
+				ReactiveAdapter reactiveAdapter = reactiveAdapterRegistry.getAdapter(parameterType);
+				if (reactiveAdapter == null || reactiveAdapter.isNoValue()) {
+					continue;
+				}
+				Class<?>[] groups = determineValidationGroups(method.getParameters()[i]);
+				if (groups == null) {
+					continue;
+				}
+				SpringValidatorAdapter validatorAdapter = validatorAdapterSupplier.get();
+				MethodParameter param = new MethodParameter(method, i);
+				arguments[i] = (reactiveAdapter.isMultiValue() ?
+						Flux.from(reactiveAdapter.toPublisher(arguments[i])).doOnNext(value ->
+								validate(validatorAdapter, adaptViolations, target, method, param, value, groups)) :
+						Mono.from(reactiveAdapter.toPublisher(arguments[i])).doOnNext(value ->
+								validate(validatorAdapter, adaptViolations, target, method, param, value, groups)));
+			}
+			return arguments;
+		}
+
+		@Nullable
+		private static Class<?>[] determineValidationGroups(Parameter parameter) {
+			Validated validated = AnnotationUtils.findAnnotation(parameter, Validated.class);
+			if (validated != null) {
+				return validated.value();
+			}
+			Valid valid = AnnotationUtils.findAnnotation(parameter, Valid.class);
+			if (valid != null) {
+				return new Class<?>[0];
+			}
+			return null;
+		}
+
+		@SuppressWarnings("unchecked")
+		private static <T> void validate(
+				SpringValidatorAdapter validatorAdapter, boolean adaptViolations,
+				Object target, Method method, MethodParameter parameter, Object argument, Class<?>[] groups) {
+
+			if (adaptViolations) {
+				Errors errors = new BeanPropertyBindingResult(argument, argument.getClass().getSimpleName());
+				validatorAdapter.validate(argument, errors);
+				if (errors.hasErrors()) {
+					ParameterErrors paramErrors = new ParameterErrors(parameter, argument, errors, null, null, null);
+					List<ParameterValidationResult> results = Collections.singletonList(paramErrors);
+					throw new MethodValidationException(MethodValidationResult.create(target, method, results));
+				}
+			}
+			else {
+				Set<ConstraintViolation<T>> violations = validatorAdapter.validate((T) argument, groups);
+				if (!violations.isEmpty()) {
+					throw new ConstraintViolationException(violations);
+				}
+			}
+		}
+	}
+
 }