Expose validateIfApplicable and isBindExceptionRequired as protected extension points in ModelAttributeMethodArgumentResolver

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolver.java

@@ -144,7 +144,7 @@ public Mono<Object> resolveArgument(
 									return adapter.fromPublisher(mono);
 								}
 								else {
-									if (errors.hasErrors() && !hasErrorsArgument(parameter)) {
+									if (errors.hasErrors() && isBindExceptionRequired(parameter)) {
 										throw new WebExchangeBindException(parameter, errors);
 									}
 									return attribute;
@@ -219,13 +219,30 @@ protected Mono<Void> bindRequestParameters(WebExchangeDataBinder binder, ServerW
 		return binder.bind(exchange);
 	}
 
-	private boolean hasErrorsArgument(MethodParameter parameter) {
+	/**
+	 * Whether to raise a fatal bind exception on validation errors.
+	 * @param parameter the method parameter declaration
+	 * @return {@code true} if the next method parameter is not of type {@link Errors}
+	 * @since 6.2
+	 */
+	protected boolean isBindExceptionRequired(MethodParameter parameter) {
 		int i = parameter.getParameterIndex();
 		Class<?>[] paramTypes = parameter.getExecutable().getParameterTypes();
-		return (paramTypes.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
+		return !(paramTypes.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
 	}
 
-	private void validateIfApplicable(WebExchangeDataBinder binder, MethodParameter parameter, ServerWebExchange exchange) {
+	/**
+	 * Validate the model attribute if applicable.
+	 * <p>The default implementation checks for {@code @jakarta.validation.Valid},
+	 * Spring's {@link org.springframework.validation.annotation.Validated},
+	 * and custom annotations whose name starts with "Valid".
+	 * @param binder the DataBinder to be used
+	 * @param parameter the method parameter declaration
+	 * @param exchange the current exchange
+	 * @see WebExchangeDataBinder#validate(Object...)
+	 * @see org.springframework.validation.SmartValidator#validate(Object, Errors, Object...)
+	 */
+	protected void validateIfApplicable(WebExchangeDataBinder binder, MethodParameter parameter, ServerWebExchange exchange) {
 		LocaleContext localeContext = null;
 		try {
 			for (Annotation ann : parameter.getParameterAnnotations()) {

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

@@ -37,6 +37,7 @@
 import org.springframework.web.bind.annotation.ModelAttribute;
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
 import org.springframework.web.bind.support.WebExchangeBindException;
+import org.springframework.web.bind.support.WebExchangeDataBinder;
 import org.springframework.web.reactive.BindingContext;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest;
@@ -400,6 +401,29 @@ void bindDataClass() {
 
 	// TODO: SPR-15871, SPR-15542
 
+	@Test
+	void protectedMethodsCanBeOverridden() {
+		// Test that validateIfApplicable and isBindExceptionRequired can be overridden
+		CustomModelAttributeMethodArgumentResolver resolver = new CustomModelAttributeMethodArgumentResolver(
+				ReactiveAdapterRegistry.getSharedInstance(), false);
+		assertThat(resolver.validateIfApplicableCalled).isFalse();
+		assertThat(resolver.isBindExceptionRequiredCalled).isFalse();
+
+		MethodParameter parameter = this.testMethod.annotPresent(ModelAttribute.class).arg(Pojo.class);
+
+		// Use invalid data to trigger validation errors, which will call isBindExceptionRequired
+		try {
+			resolver.resolveArgument(parameter, this.bindContext, postForm("name=Robert&age=invalid"))
+					.block(Duration.ZERO);
+		}
+		catch (WebExchangeBindException ex) {
+			// Expected - validation error
+		}
+
+		assertThat(resolver.validateIfApplicableCalled).isTrue();
+		assertThat(resolver.isBindExceptionRequiredCalled).isTrue();
+	}
+
 
 	private ModelAttributeMethodArgumentResolver createResolver() {
 		return new ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance(), false);
@@ -516,7 +540,7 @@ public String getName() {
 		}
 
 		public int getAge() {
-			return this.age;
+			return age;
 		}
 
 		public int getCount() {
@@ -528,4 +552,30 @@ public void setCount(int count) {
 		}
 	}
 
+
+	/**
+	 * Custom resolver that overrides protected methods to verify they can be extended.
+	 */
+	private static class CustomModelAttributeMethodArgumentResolver extends ModelAttributeMethodArgumentResolver {
+
+		boolean validateIfApplicableCalled = false;
+		boolean isBindExceptionRequiredCalled = false;
+
+		public CustomModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry adapterRegistry, boolean useDefaultResolution) {
+			super(adapterRegistry, useDefaultResolution);
+		}
+
+		@Override
+		protected void validateIfApplicable(WebExchangeDataBinder binder, MethodParameter parameter, ServerWebExchange exchange) {
+			this.validateIfApplicableCalled = true;
+			super.validateIfApplicable(binder, parameter, exchange);
+		}
+
+		@Override
+		protected boolean isBindExceptionRequired(MethodParameter parameter) {
+			this.isBindExceptionRequiredCalled = true;
+			return super.isBindExceptionRequired(parameter);
+		}
+	}
+
 }