Built-in support for standard bean validation on controller method arguments

[hedgerocker]

Related to #11041.

I'm trying to validate @PathVariable and @RequestBody in one method. MethodValidationPostProcessor is registered. Simplified Controller looks like this:

@RestController
@Validated
public class MyController {
    @RequestMapping(value = "/{id}", method = RequestMethod.PUT)
    public ResponseEntity method_name(@PathVariable @NotNull String id, @Valid @RequestBody Body body) {
        /// Some code
    }
}

I noticed that request body validation is triggered twice - it wouldn't be an issue if it weren't custom ConstraintValidator with injected bean:

public class CustomValidator implements ConstraintValidator<Body, String> {

	@Autowired
	private BodyVerificator bodyVerificator;
...

For first validation run the bean is injected properly, and for second run it's null so it results in NPE. Workaround is to either not use method parameter validation at all, or to annotate @RequestBody with @Validated so not mix @Validated and @Valid. I would actually prefer to have @PathVariable bean validation support in Spring like in #11041.

[encircled]

Hi,

Use annotation @Validated instead of @Valid for @RequestBody parameter. Then MethodValidationPostProcessor will not be triggered and Spring arguments validation (with dependencies injection for validators) will still work.

[rstoyanchev]

Team decision: we are going to provide first-class support for bean validation that's built at the web framework level (Spring MVC and WebFlux), without requiring a separate post-processor and an AOP proxy.

[rstoyanchev]

I'm closing this in favor of #29825 that summarizes issues with validation across multiple issues, and also highlights some of the design questions. Please take a look and provide further feedback if necessary under the new issue.