js受信バックグラウンドバイナリはファイル形式になります.

    
    @RequestMapping(value = "/audit", method = {RequestMethod.POST, RequestMethod.GET})
    @ResponseBody
    public void audit(@RequestParam("id") long id, @RequestParam("status") String status,HttpServletResponse response) {
        JsonObject jsonObject = new JsonObject();
        try {
           
                String redeemCodeString="";
            
                response.reset();
                OutputStream outputStream = new BufferedOutputStream(response.getOutputStream());
                response.setContentType("application/octet-stream");
                response.setHeader("Content-Disposition","attachment; filename="+"redeemCodeString.txt");
                outputStream.write(redeemCodeString.getBytes(),0,redeemCodeString.getBytes().length);
                outputStream.close();
            

        } catch (Exception e) {
            e.printStackTrace();
            jsonObject.addProperty("msg","    ！");
            jsonObject.addProperty("code",1);
        }
    }

            var xhr = new XMLHttpRequest();
	    var str = "id=" + ticketId + "&status=" + status;
            xhr.open('POST', "/admin/audit", true);    //     POST  ，    
            xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
            xhr.responseType = "blob";   //    blob
            xhr.onload = function () {
                //           
                if (this.status === 200) {
                        var blob = this.response;
                        if(blob.size>0){
                            var reader = new FileReader();
                            reader.readAsDataURL(blob);   //    base64，      a  href
                            reader.onload = function (e) {
                                //     ，    a      
                                var a = document.createElement('a');
                                a.download = '   .txt';
                                a.href = e.target.result;
                                $("body").append(a);    //   firefox     click
                                a.click();
                                $(a).remove();
                                window.location.reload();
                            }
                        }else{
                            window.location.reload();
						}
                }
            };
            xhr.send(str);