How to respond with HTTP 400 error in a Spring MVC @ResponseBody method returning String?

Question

I'm using Spring MVC for a simple JSON API, with @ResponseBody based approach like the following. (I already have a service layer producing JSON directly.)

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        // TODO: how to respond with e.g. 400 "bad request"?
    }
    return json;
}

Question is, in the given scenario, what is the simplest, cleanest way to respond with a HTTP 400 error?

I did come across approaches like:

return new ResponseEntity(HttpStatus.BAD_REQUEST);

...but I can't use it here since my method's return type is String, not ResponseEntity.

Answer 1

change your return type to ResponseEntity<>, then you can use below for 400

return new ResponseEntity<>(HttpStatus.BAD_REQUEST);

and for correct request

return new ResponseEntity<>(json,HttpStatus.OK);

UPDATE 1

after spring 4.1 there are helper methods in ResponseEntity could be used as

return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(null);

and

return ResponseEntity.ok(json);