Ajax发布请求contentType

I created a html form with multipart, I should form a request with form fields and a file which is uploaded. I used ajax POST request but I don't know exactly which contentType to use. tried with 'multipart/form-data' but I get BadRequest from server.

        var fd = new FormData();
        fd.append('name',"somename");
        fd.append('regionalName',"newString");
        fd.append('constituencyNumber',122);
        fd.append('districtId',21);
        fd.append('file',document.getElementById('filePicker').files[0]);

        ajax({
           url: "http://192.168.1.157:8080/constituency",
           type: "POST",
           data:fd,
           contentType: false,
           processData: false,
           cache: false,
           success: function () {
               console.log("success");
           },
           error: function () {
               console.log("filaed");
           }
        });

In server side

@RequestMapping(value="/constituency", method=RequestMethod.POST)
    public BaseResponseDto addConstituency(@RequestBody FormDataMultiPart constituencyDto){
        log.info("addConstituency");
        return constituencyService.addConstituency(constituencyDto);
    }

Request not reach my controller. Anything I missed out!!