Spring MVC and WebFlux handling of method validation errors

[rstoyanchev]

The new MethodValidationException introduced as part of #29825 needs to have default handling in Spring MVC and WebFlux, including RFC 7807 support, similar to the handling of BindException but reflecting errors for multiple method parameters / or return value, represented with ParameterValidationResult and ParameterErrors.

[rstoyanchev]

There is now a new HandlerMethodValidationException, similar to the MethodValidationException raised when method validation is applied via AOP (to any Spring component), but extending from ResponseStatusException and thrown from the built-in method validation support for @RequestMapping methods.

The new exception is handled in ResponseEntityExceptionHandler and in DefaultHandlerExceptionResolver
as e 400 error if is for method arguments, and as a 500 error if it is for a return value. MethodValidationException (possibly from an underlying service) is handled as a 500 error.

By default for RFC 7807, the detail of ProblemDetail is just a short message "Validation failure". You can customize that with a MessageSource as described in the reference documentation where the {0} argument for HandlerMethodValidationException is the list of all errors. For more control, handle this exception directly and provide it with a Visitor to handle controller method parameters individually.

[ctapobep]

From the documentation it's not clear - does this mean that the old MethodArgumentNotValidException isn't going to be used by Spring MVC anymore? We should always expect HandlerMethodValidationException on the API level from now on?