How to Return HTTP 400 Errors from Spring MVC @ResponseBody Methods Returning Strings?

Handling HTTP 400 Errors in Spring MVC @ResponseBody Methods Returning String

In Spring MVC, it's common to use @ResponseBody for JSON APIs. However, handling errors can be challenging when the method returns a String. This article explores the simplest way to respond with an HTTP 400 error in such scenarios.

In the example provided:

@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;
}

To return an HTTP 400 error, the simplest approach is to modify the return type of the method to ResponseEntity<>. This will allow you to use the following code for 400 responses:

return new ResponseEntity<>(HttpStatus.BAD_REQUEST);

For successful requests, you can use:

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

Alternatively, for Spring 4.1 and later, you can leverage helper methods in ResponseEntity:

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

And for successful requests:

return ResponseEntity.ok(json);

By using ResponseEntity<>, you can easily handle HTTP errors in your @ResponseBody methods while maintaining a straightforward and clean implementation.

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