How to return 404 response status in Spring Boot @ResponseBody - method return type is Response?

This is very simply done by throwing org.springframework.web.server.ResponseStatusException:

throw new ResponseStatusException(
  HttpStatus.NOT_FOUND, "entity not found"
);

It's compatible with @ResponseBody and with any return value. Requires Spring 5+

Create a NotFoundException class with an @ResponseStatus(HttpStatus.NOT_FOUND) annotation and throw it from your controller.

@ResponseStatus(code = HttpStatus.NOT_FOUND, reason = "video not found")
public class VideoNotFoundException extends RuntimeException {
}

Your original method can return ResponseEntity (doesn't change your method behavior):

@RequestMapping(value = VIDEO_DATA_PATH, method = RequestMethod.GET)
public ResponseEntity getData(@PathVariable(ID_PARAMETER) long id, HttpServletResponse res{
... 
}

and return the following:

return new ResponseEntity(HttpStatus.NOT_FOUND);