#RestController: Validate the #ResponseBody (not the #RequestBody) - spring

Question

How can I achive that the #ResponseBody (in my case a class of type SomePojoInterface) is automatically validated (lets say through JSR-303 validation). Nice to have would be, that in case of a validation-failure the handler would throw an Exception which can be handled in some #ControllerAdvice annotated class.
My code so far.
#RestController
public class MyRestController {
#GetMapping(value = "validate", produces = MediaType.APPLICATION_JSON_VALUE)
#ResponseBody
protected SomePojo validateResponse() {
return new SomePojo();
}
}
#ControllerAdvice
class GlobalControllerExceptionHandler {
#ResponseStatus(HttpStatus.XXX)
#ExceptionHandler(MyResponseValidationException.class)
public void handleResponseValidationException() {
// ...
}
}
public class SomePojo implements SomePojoInterface {
#NotNull
private String someValue;
// getter / setter
}

Answer 1

If you have annotated your class SomePojo, then:
#GetMapping(value = "validate", produces = MediaType.APPLICATION_JSON_VALUE)
protected SomePojo validateResponse() {
ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
Validator validator = factory.getValidator();
SomePojo somePojo = new SomePojo(null);
Set<ConstraintViolation<Car>> constraintViolations = validator.validate(somePojo);
// Other stuff
}
#Valid annotation is for request. More examples from their docs. I am not sure what all you want to validate

Answer 2

I managed to achieve this through the #RestControllerAdvice.
#RestControllerAdvice
public class RestPostProcessingAdvice implements ResponseBodyAdvice<SomePojoInterface> {
#Inject
private Validator validator;
#Override
public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
if(doSomeChecksIfEligiable(returnType, converterType)) {
return true;
}
return false;
}
#Override
public SomePojoInterface beforeBodyWrite(SomePojoInterface body, MethodParameter returnType,
MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType,
ServerHttpRequest request, ServerHttpResponse response) {
Set<ConstraintViolation<Object>> constraintViolations = validator.validate(body);
if(constraintViolations.size() > 0) {
response.setStatusCode(HttpStatus.XXX);
LOG.fatal("Sorry, I'm sending crap");
}
return body;
}
}
Be aware that throwing an Exception and catching it in an #ExceptionHandler that is sending the same (mofified) object out in the #ResponseBody could lead to an endless loop, since the object will be checked again this #RestControllerAdvice.