[Java知识库]Springboot 中使用 RestTemplate 向另一个 RESTful api 请求 multipart file 报错

No serializer found for class java.io.FileDescriptor

如第三方的文件上传接口：
?

        /**
         * 上传文件
         * @param request
         * @param response
         * @param file
         * @param sysFile
         * @return
         */
        @RequestMapping(value = "/sysFile/uploadFile", method = RequestMethod.POST, produces = "text/html;charset=utf-8")
        @ResponseBody
        public Object uploadFile(HttpServletRequest request, HttpServletResponse response, @RequestParam("file") MultipartFile file, SysFile sysFile, String crossDomain) {
                Json json = sysFileService.updateUploadFile(file, sysFile);
                String str = JSONObject.toJSONString(json);

                if (!StringUtil.isBlank(crossDomain) && crossDomain.equals("1")){
                        return "<script type='text/javascript'>var result='" + str + "';window.parent.postMessage(result, '*')</script>";
                } else {
                        return str;
                }
        }

需要注意：

# 1. multiValueMap设置的"file" ，需要进行文件转化处理
# 2. 设置head为 headers.setContentType(MediaType.MULTIPART_FORM_DATA);

调用这接口时:

   
# /sysFile/uploadFile 为第三方接口，

# 1. multiValueMap设置的"file" ，需要进行文件转化处理
# 2. 设置head为 headers.setContentType(MediaType.MULTIPART_FORM_DATA);


 String thirdUrl = "https://xxxx.net/xxbb" + "/sysFile/uploadFile";
        MultiValueMap<String, Object> multiValueMap = new LinkedMultiValueMap<>();
        multiValueMap.add("fileProvenance", 1);
        multiValueMap.add("fileType", 1);
        multiValueMap.add("fileSerialNo", 1);
        //multiValueMap.add("file", file);
        multiValueMap.add("file", new FileSystemResource(convert(file)));




public File convert(MultipartFile file)
    {
        File convFile = new File("temp_image", file.getOriginalFilename());
        if (!convFile.getParentFile().exists()) {
            System.out.println("mkdir:" + convFile.getParentFile().mkdirs());
        }
        try {
            convFile.createNewFile();
            FileOutputStream fos = new FileOutputStream(convFile);
            fos.write(file.getBytes());
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return convFile;
    }

    private static volatile RestTemplate restTemplate;



    public static R postWithFormFile(String url, MultiValueMap<String, Object> multiValueMap) {
        try {
            HttpHeaders headers = new HttpHeaders();
            headers.setContentType(MediaType.MULTIPART_FORM_DATA);
            HttpEntity<MultiValueMap<String, Object>> httpEntity = new HttpEntity(multiValueMap, headers);
            ResponseEntity<String> responseEntity = getRestTemplate().postForEntity(url, httpEntity, String.class, new Object[0]);
            logger.info("调用第三方服务,url为:{}, 返回结果为:{}", url, JSONObject.toJSONString(responseEntity));
            if (!ObjectUtil.isEmpty(responseEntity) && responseEntity.getStatusCodeValue() == 200) {
                String body = (String)responseEntity.getBody();
                return R.data(body);
            } else {
                return R.fail(ResultCode.THIRD_REQUEST_FAIL);
            }
        } catch (RestClientException var6) {
            logger.error("调用第三方应用请求异常,异常原因:{}", var6.getMessage());
            return R.fail(ResultCode.FAILURE);
        }
    }

    private static RestTemplate getRestTemplate() {
        if (ObjectUtil.isEmpty(restTemplate)) {
            Class var0 = RestTemplateUtil.class;
            synchronized(RestTemplateUtil.class) {
                SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
                factory.setReadTimeout(100000);
                factory.setConnectTimeout(10000);
                restTemplate = new RestTemplate(factory);
            }
        }

        return restTemplate;
    }

参考：
Springboot 中使用 RestTemplate 向另一个 RESTful api 请求 multipart file 报错_thothsun 的博客-CSDN博客