Spring mvc webservice : input control "validator" - web-services

Question

Here is an example of my webservice:
#Override
#RequestMapping(value="{width}/{height}/{limit}", method = RequestMethod.POST)
public #ResponseBody ThumbnailResponse createThumbnails(#PathVariable int width, #PathVariable int height, #PathVariable int limit) {
List<String> list = thumbnailService.processImages(width,height,limit);
return new ThumbnailResponse(list.size(),list);
}
What I want to do is to answer a 400 BAD REQUEST to the user if the value of width or height is less than 10.
I need a kind of "REST Validator" before sending the response to the user. How can I do that ?
Thanks.

Answer 1

The approach I would follow is based on Spring MVC exception handling
What it means in practice is that:
You make a custom exception
Change your controller method accordingly
Catch the exception in your exception handler, and set the proper status and message
In terms of code it would mean
public class HeightNotAllowedException extends Exception {
}
Change in the controller
#Override
#RequestMapping(value="{width}/{height}/{limit}", method = RequestMethod.POST)
public #ResponseBody ThumbnailResponse createThumbnails(#PathVariable int width, #PathVariable int height, #PathVariable int limit) throws HeightNotAllowedException {
if (height < 10) {
throw new HeightNotAllowedException();
}
List<String> list = thumbnailService.processImages(width,height,limit);
return new ThumbnailResponse(list.size(),list);
}
Global exception handler (though you can go for per controller one)
#ControllerAdvice
public class GlobalErrorHandler {
#ExceptionHandler(value = HeightNotAllowedException.class)
#ResponseBody
#ResponseStatus(value = HttpStatus.BAD_REQUEST, reason = "Invalid Height")
public String heightError(HeightNotAllowedException ex) {
LOGGER.error("Invalid height");
return "Invalid Height";
}
}

Answer 2

Although there are couple of ways, for this case you can do just like below.
#Override
#RequestMapping(value="{width}/{height}/{limit}", method = RequestMethod.POST)
public #ResponseBody ResponseEntity createThumbnails(#PathVariable int width, #PathVariable int height, #PathVariable int limit) {
Gson gson = new Gson();
if(width <10 || height <10){
return new ResponseEntity<String>(HttpStatus.BAD_REQUEST);
}
List<String> list = thumbnailService.processImages(width,height,limit);
ThumbnailResponse response = new ThumbnailResponse(list.size(),list);
return new ResponseEntity<String>(gson.toJson(response), HttpStatus.OK);
}
However the standard way is to write Validator for the object and there is a method validate,Inside which you can write your validation logic and
class YourValidator implements Validator{
public void validate(Object target, Errors errors) {
//write your validation logic
}
}
and from your controller you can use it and validate the response like below.
if(error.hasErrors()){
return new ResponseEntity<String>(HttpStatus.BAD_REQUEST);
}