求助： springmvc 上传至 mongodb 后下载文件无法打开

RT 球球大佬们帮忙看看是哪里出了问题
----上传


/**
*
*接受前端上传的文件并存储至 MongoDB
* @param file 前端上传的文件
* @return 处理结果信息
*/
@CrossOrigin
@ResponseBody
@RequestMapping(value = "/upload", method = RequestMethod.POST)
public ReturnInfo fileUpload(@RequestParam MultipartFile file) throws Exception {
ReturnInfo<Map> info = new ReturnInfo<>();
if (!file.isEmpty()) {
BufferedInputStream inputStream = new BufferedInputStream(file.getInputStream());
String fileId = fileService.fileUpload(inputStream);
info.setCode(ReturnInfo.OK);
info.setMessage("上传成功！");
Map<String, String> resultMap = new HashMap<>();
resultMap.put("fileId", fileId);
info.setData(resultMap);
return info;
} else {
info.setMessage("文件不能为空");
info.setCode(ReturnInfo.ERROR);
return info;
}

}

/**
* 文件上传 service
*
* @param fileInput 文件输入流
* @return mongodb 对应文件 id
*/
@Override
public String fileUpload(InputStream fileInput) throws RestServiceException {
String fileType = FileUtil.getFileType(fileInput);
System.out.println(fileType);
//文件类型判断
if (!FileUtil.ENABLE_TYPES.contains(fileType)) {
throw new RestServiceException("不支持的文件类型！");
}
GridFSFile uploadFile = gridFsTemplate.store(fileInput, StringUtil.getUUID(), fileType);
return uploadFile.getId().toString();
}

----下载





/**下载请求
* 下载文件
*
* @param fileId 文件 ID
* @return
*/
@CrossOrigin
@RequestMapping(value = "/download2/{fileId}", method = RequestMethod.GET)
@ResponseBody
public ResponseEntity<InputStreamResource> fileDownload2(@PathVariable String fileId) throws Exception {
//从 MongoDB 获取文件
GridFSDBFile file = fileService.getFileById(fileId);
String fileType = file.getContentType();
//设置文件 ContentType
MediaType mediaType = FileUtil.getEnableStr(fileType);
InputStreamResource resource = new InputStreamResource(file.getInputStream());
HttpHeaders headers = new HttpHeaders();
headers.setContentType(mediaType);
headers.setContentDispositionFormData("attachment",file.getFilename()+"."+fileType);
//返回前端
return new ResponseEntity<>(resource, headers, HttpStatus.OK);
}

/**
*下载 service
*/
@Override
public GridFSDBFile getFileById(String fileId) throws RestServiceException {
GridFSDBFile file = gridFsTemplate.findOne(Query.query(Criteria.where("_id").is(fileId)));
if (file == null) {
throw new RestServiceException("找不到相关文件！请检查 fileId");
}
return file;
}