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

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'm new to Spring MVC, and this turned out somewhat non-obvious... 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.

Answers

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

return new ResponseEntity<String>(HttpStatus.BAD_REQUEST);

and for correct request

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

Something like this should work, I'm not sure whether or not there is a simpler way:

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId, @RequestBody String body,
            HttpServletRequest request, HttpServletResponse response) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        response.setStatus( HttpServletResponse.SC_BAD_REQUEST  );
    }
    return json;
}

source - http://stackoverflow.com/questions/16232833/how-to-respond-with-http-400-error-in-a-spring-mvc-responsebody-method-returnin

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