Spring get MediaType of received body

Following this answer I've set my method in controller this way:

@PostMapping(path = PathConstants.START_ACTION, consumes = {MediaType.APPLICATION_FORM_URLENCODED_VALUE, MediaType.APPLICATION_JSON_VALUE})
    public ResponseEntity<BaseResponse<ProcessInstance>> start(@PathVariable String processDefinitionId,
            @RequestBody(required = false) String params)

Now I need to behave differently according to my @RequestBody being of one MediaType or the other, so I need to know whether my params body is json o urlencoded. Is there a way to do this?

You can simply inject Content-Type header.

    @PostMapping(path = "/{processDefinitionId}", consumes = {MediaType.APPLICATION_FORM_URLENCODED_VALUE, MediaType.APPLICATION_JSON_VALUE})
    public ResponseEntity<String> start(@PathVariable String processDefinitionId,
                                        @RequestBody(required = false) String params,
                                        @RequestHeader("Content-Type") String contentType) {
        if (contentType.startsWith(MediaType.APPLICATION_JSON_VALUE)) {
            System.out.println("json");
        } else {
            // ...
        }
        return ResponseEntity.ok(params);
    }

But I would suggest to split this method on two methods with different consumes values:

    @PostMapping(path = "/v2/{processDefinitionId}", consumes = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<String> startV2Json(@PathVariable String processDefinitionId,
                                        @RequestBody(required = false) String params) {
        return ResponseEntity.ok(params);
    }

    @PostMapping(path = "/v2/{processDefinitionId}", consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
    public ResponseEntity<String> startV2UrlEncoded(@PathVariable String processDefinitionId,
                                        @RequestBody(required = false) String params) {
        return ResponseEntity.ok(params);
    }