Document method validation improvements

Closes gh-30643

Author: rstoyanchev

framework-docs/modules/ROOT/nav.adoc

@@ -267,6 +267,7 @@
 ***** xref:web/webmvc/mvc-controller/ann-methods/jackson.adoc[]
 **** xref:web/webmvc/mvc-controller/ann-modelattrib-methods.adoc[]
 **** xref:web/webmvc/mvc-controller/ann-initbinder.adoc[]
+**** xref:web/webmvc/mvc-controller/ann-validation.adoc[]
 **** xref:web/webmvc/mvc-controller/ann-exceptionhandler.adoc[]
 **** xref:web/webmvc/mvc-controller/ann-advice.adoc[]
 *** xref:web/webmvc-functional.adoc[]
@@ -361,6 +362,7 @@
 ***** xref:web/webflux/controller/ann-methods/jackson.adoc[]
 **** xref:web/webflux/controller/ann-modelattrib-methods.adoc[]
 **** xref:web/webflux/controller/ann-initbinder.adoc[]
+**** xref:web/webflux/controller/ann-validation.adoc[]
 **** xref:web/webflux/controller/ann-exceptions.adoc[]
 **** xref:web/webflux/controller/ann-advice.adoc[]
 *** xref:web/webflux-functional.adoc[]

framework-docs/modules/ROOT/pages/core/validation/beanvalidation.adoc

@@ -123,15 +123,12 @@ Validator, is expected to be present in the classpath and is automatically detec
 
 
 [[validation-beanvalidation-spring-inject]]
-=== Injecting a Validator
+=== Inject Jakarta Validator
 
 `LocalValidatorFactoryBean` implements both `jakarta.validation.ValidatorFactory` and
-`jakarta.validation.Validator`, as well as Spring's `org.springframework.validation.Validator`.
-You can inject a reference to either of these interfaces into beans that need to invoke
-validation logic.
-
-You can inject a reference to `jakarta.validation.Validator` if you prefer to work with the Bean
-Validation API directly, as the following example shows:
+`jakarta.validation.Validator`, so you can inject a reference to the latter to
+apply validation logic if you prefer to work with the Bean Validation API directly,
+as the following example shows:
 
 [tabs]
 ======
@@ -160,8 +157,15 @@ Kotlin::
 ----
 ======
 
-You can inject a reference to `org.springframework.validation.Validator` if your bean
-requires the Spring Validation API, as the following example shows:
+
+[[validation-beanvalidation-spring-inject-adapter]]
+=== Inject Spring Validator
+
+In addition to implementing `jakarta.validation.Validator`, `LocalValidatorFactoryBean`
+also adapts to `org.springframework.validation.Validator`, so you can inject a reference
+to the latter if your bean requires the Spring Validation API.
+
+For example:
 
 [tabs]
 ======
@@ -190,9 +194,15 @@ Kotlin::
 ----
 ======
 
+When used as `org.springframework.validation.Validator`, `LocalValidatorFactoryBean`
+invokes the underlying `jakarta.validation.Validator`, and then adapts
+``ContraintViolation``s to ``FieldError``s, and registers them with the `Errors` object
+passed into the `validate` method.
+
+
 
 [[validation-beanvalidation-spring-constraints]]
-=== Configuring Custom Constraints
+=== Configure Custom Constraints
 
 Each bean validation constraint consists of two parts:
 
@@ -274,9 +284,8 @@ As the preceding example shows, a `ConstraintValidator` implementation can have
 [[validation-beanvalidation-spring-method]]
 === Spring-driven Method Validation
 
-You can integrate the method validation feature supported by Bean Validation 1.1 (and, as
-a custom extension, also by Hibernate Validator 4.3) into a Spring context through a
-`MethodValidationPostProcessor` bean definition:
+You can integrate the method validation feature of Bean Validation into a
+Spring context through a `MethodValidationPostProcessor` bean definition:
 
 [tabs]
 ======
@@ -305,11 +314,11 @@ XML::
 ----
 ======
 
-To be eligible for Spring-driven method validation, all target classes need to be annotated
+To be eligible for Spring-driven method validation, target classes need to be annotated
 with Spring's `@Validated` annotation, which can optionally also declare the validation
 groups to use. See
 {api-spring-framework}/validation/beanvalidation/MethodValidationPostProcessor.html[`MethodValidationPostProcessor`]
-for setup details with the Hibernate Validator and Bean Validation 1.1 providers.
+for setup details with the Hibernate Validator and Bean Validation providers.
 
 [TIP]
 ====
@@ -320,6 +329,61 @@ xref:core/aop/proxying.adoc#aop-understanding-aop-proxies[Understanding AOP Prox
 to always use methods and accessors on proxied classes; direct field access will not work.
 ====
 
+By default, `jakarta.validation.ConstraintViolationException` is raised with the set of
+``ConstraintViolation``s returned by `jakarata.validation.Validator`. As an alternative,
+you can have `MethodValidationException` raised instead with ``ConstraintViolation``s
+adapted to `MessageSourceResolvable` errors. To enable set the following flag:
+
+[tabs]
+======
+Java::
++
+[source,java,indent=0,subs="verbatim,quotes",role="primary"]
+----
+	import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
+
+	@Configuration
+	public class AppConfig {
+
+		@Bean
+		public MethodValidationPostProcessor validationPostProcessor() {
+			MethodValidationPostProcessor processor = new MethodValidationPostProcessor();
+			processor.setAdaptConstraintViolations(true);
+			return processor;
+		}
+	}
+
+----
+
+XML::
++
+[source,xml,indent=0,subs="verbatim,quotes",role="secondary"]
+----
+	<bean class="org.springframework.validation.beanvalidation.MethodValidationPostProcessor">
+		<property name="adaptConstraintViolations" value="true"/>
+	</bean>
+----
+======
+
+`MethodValidationException` contains a list of ``ParameterValidationResult``s which
+group errors by method parameter, and each exposes a `MethodParameter`, the argument
+value, and a list of `MessageSourceResolvable` errors adapted from
+``ConstraintViolation``s. For `@Valid` method parameters with cascaded violations on
+fields and properties, the `ParameterValidationResult` is `ParameterErrors` which
+implements `org.springframework.validation.Errors` and exposes validation errors as
+``FieldError``s.
+
+The adapted `MessageSourceResolvable` errors can be turned into error messages to
+display to users through the configured
+xref:core/beans/context-introduction.adoc#context-functionality-messagesource[`MessageSource`]
+based on locale and language specific resource bundles.
+
+NOTE: Spring MVC and WebFlux have built-in support for method validation, and therefore
+for web controller methods there is no need for a class level `@Validated` and an AOP proxy.
+See the Spring MVC xref:web/webmvc/mvc-controller/ann-validation.adoc[Validation] section,
+the WebFlux xref:web/webflux/controller/ann-validation.adoc[Validation] section,
+and the xref:web/webmvc/mvc-controller/ann-validation.adoc[Error Responses] section.
+
 
 
 

framework-docs/modules/ROOT/pages/web/webflux/ann-rest-exceptions.adoc

@@ -67,23 +67,23 @@ from an existing `ProblemDetail`. This could be done centrally, e.g. from an
 
 
 [[webflux-ann-rest-exceptions-i18n]]
-== Internationalization
+== Customization and i18n
 [.small]#xref:web/webmvc/mvc-ann-rest-exceptions.adoc#mvc-ann-rest-exceptions-i18n[See equivalent in the Servlet stack]#
 
-It is a common requirement to internationalize error response details, and good practice
-to customize the problem details for Spring WebFlux exceptions. This section describes the
-support for that.
+It is a common requirement to customize and internationalize error response details.
+It is also good practice to customize the problem details for Spring WebFlux exceptions
+to avoid revealing implementation details. This section describes the support for that.
 
-`ErrorResponse` exposes message codes for "type", "title", and "detail", in addition to
+An `ErrorResponse` exposes message codes for "type", "title", and "detail", as well as
 message code arguments for the "detail" field. `ResponseEntityExceptionHandler` resolves
 these through a xref:core/beans/context-introduction.adoc#context-functionality-messagesource[MessageSource]
-and updates the `ProblemDetail` accordingly.
+and updates the corresponding `ProblemDetail` fields accordingly.
 
 The default strategy for message codes follows the pattern:
 
 `problemDetail.[type|title|detail].[fully qualified exception class name]`
 
-Some `ErrorResponse` may expose more than one message code, typically adding a suffix
+An `ErrorResponse` may expose more than one message code, typically adding a suffix
 to the default message code. The table below lists message codes, and arguments for
 Spring WebFlux exceptions:
 
@@ -92,28 +92,19 @@ Spring WebFlux exceptions:
 |===
 | Exception | Message Code | Message Code Arguments
 
-| `UnsupportedMediaTypeStatusException`
+| `HandlerMethodValidationException`
 | (default)
-| `+{0}+` the media type that is not supported, `+{1}+` list of supported media types
+| `+{0}+` list all validation errors.
+Message codes and arguments for each error are also resolved via `MessageSource`.
 
-| `UnsupportedMediaTypeStatusException`
-| (default) + ".parseError"
-|
+| `MethodNotAllowedException`
+| (default)
+| `+{0}+` the current HTTP method, `+{1}+` the list of supported HTTP methods
 
 | `MissingRequestValueException`
 | (default)
 | `+{0}+` a label for the value (e.g. "request header", "cookie value", ...), `+{1}+` the value name
 
-| `UnsatisfiedRequestParameterException`
-| (default)
-| `+{0}+` the list of parameter conditions
-
-| `WebExchangeBindException`
-| (default)
-| `+{0}+` the list of global errors, `+{1}+` the list of field errors.
-Message codes and arguments for each error within the `BindingResult` are also resolved
-via `MessageSource`.
-
 | `NotAcceptableStatusException`
 | (default)
 | `+{0}+` list of supported media types
@@ -126,9 +117,22 @@ via `MessageSource`.
 | (default)
 | `+{0}+` the failure reason provided to the class constructor
 
-| `MethodNotAllowedException`
+| `UnsupportedMediaTypeStatusException`
 | (default)
-| `+{0}+` the current HTTP method, `+{1}+` the list of supported HTTP methods
+| `+{0}+` the media type that is not supported, `+{1}+` list of supported media types
+
+| `UnsupportedMediaTypeStatusException`
+| (default) + ".parseError"
+|
+
+| `UnsatisfiedRequestParameterException`
+| (default)
+| `+{0}+` the list of parameter conditions
+
+| `WebExchangeBindException`
+| (default)
+| `+{0}+` the list of global errors, `+{1}+` the list of field errors.
+Message codes and arguments for each error are also resolved via `MessageSource`.
 
 |===
 

framework-docs/modules/ROOT/pages/web/webflux/controller/ann-methods/modelattrib-method-args.adoc

@@ -160,10 +160,13 @@ Kotlin::
 ----
 ======
 
-Note that use of `@ModelAttribute` is optional -- for example, to set its attributes.
-By default, any argument that is not a simple value type (as determined by
-{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty])
-and is not resolved by any other argument resolver is treated as if it were annotated
-with `@ModelAttribute`.
+If method validation applies because other parameters have `@Constraint` annotations,
+then `HandlerMethodValidationException` would be raised instead. See the section on
+controller method xref:web/webmvc/mvc-controller/ann-validation.adoc[Validation].
+
+TIP: Using `@ModelAttribute` is optional. By default, any argument that is not a simple
+value type as determined by
+{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]
+_AND_ that is not resolved by any other argument resolver is treated as an `@ModelAttribute`.
 
 

framework-docs/modules/ROOT/pages/web/webflux/controller/ann-methods/multipart-forms.adoc

@@ -176,6 +176,10 @@ Kotlin::
 ======
 --
 
+If method validation applies because other parameters have `@Constraint` annotations,
+then `HandlerMethodValidationException` is raised instead. See the section on
+xref:web/webflux/controller/ann-validation.adoc[Validation].
+
 To access all multipart data as a `MultiValueMap`, you can use `@RequestBody`,
 as the following example shows:
 
@@ -306,5 +310,3 @@ file upload.
 
 Received part events can also be relayed to another service by using the `WebClient`.
 See xref:web/webflux-webclient/client-body.adoc#webflux-client-body-multipart[Multipart Data].
-
-

framework-docs/modules/ROOT/pages/web/webflux/controller/ann-methods/requestbody.adoc

@@ -89,4 +89,33 @@ Kotlin::
 ----
 ======
 
+You can also declare an `Errors` parameter for access to validation errors, but in
+that case the request body must not be a `Mono`, and will be resolved first:
+
+[tabs]
+======
+Java::
++
+[source,java,indent=0,subs="verbatim,quotes",role="primary"]
+----
+	@PostMapping("/accounts")
+	public void handle(@Valid @RequestBody Account account, Errors errors) {
+		// use one of the onError* operators...
+	}
+----
+
+Kotlin::
++
+[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
+----
+	@PostMapping("/accounts")
+	fun handle(@Valid @RequestBody account: Mono<Account>) {
+		// ...
+	}
+----
+======
+
+If method validation applies because other parameters have `@Constraint` annotations,
+then `HandlerMethodValidationException` is raised instead. For more details, see the
+section on xref:web/webflux/controller/ann-validation.adoc[Validation].