How to pass information from ConstraintValidator to Controller? - spring

Question

I have a custom ConstraintValidator.
public class UrlValidator implements ConstraintValidator<ValidUrl, RemoteFile> {
#Override
public boolean isValid(RemoteFile value, ConstraintValidatorContext context) {
return true;
}
}
The RemoteFile is a very simple DTO.
public record RemoteFile(String url) {}
I'm using UrlValidator with my custom annotation.
#Documented
#Target(ElementType.PARAMETER)
#Retention(RetentionPolicy.RUNTIME)
#Constraint(validatedBy = UrlValidator.class)
public #interface ValidUrl {
String message() default "invalid file";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
Finally I'm using the annotation inside my controller.
#PostMapping("/hello")
public String remote(#ValidUrl #RequestBody RemoteFile body) {
// do stuff inside the controller
}
I'd like to pass some information from my validator to my controller. I found a way to do this but I was wondering why the other way does not work.
Here is what works.
#Override
public boolean isValid(RemoteFile value, ConstraintValidatorContext context) {
RequestContextHolder.getRequestAttributes()
.setAttribute("key", "value", RequestAttributes.SCOPE_REQUEST);
return true;
}
I can afterwards access the information in my controller.
#PostMapping("/hello")
public String remote(#ValidUrl #RequestBody RemoteFile body) {
var value =
(String)
RequestContextHolder.getRequestAttributes()
.getAttribute("key", RequestAttributes.SCOPE_REQUEST);
// do stuff inside the controller
}
Then I tried something different because I thought there is a simpler way. However this DOES not work and I do not understand why. Use the HttpServletRequest and set an attribute.
#Autowired HttpServletRequest request;
#Override
public boolean isValid(RemoteFile value, ConstraintValidatorContext context) {
request.setAttribute("key", "value");
return true;
}
Use the attribute directly in the controller method.
#PostMapping("/remote")
public String remote(
#ValidUrl #RequestBody RemoteFile body,
#RequestAttribute String key
) {
// do stuff in the controller
}
However I'm always getting the error message
Resolved [org.springframework.web.bind.ServletRequestBindingException: Missing request attribute 'key' of type String]
I do not understand the error message. The attribute should be there because the validator should have set it. Any ideas? I'm lost!