使用RestTemplate上传MultipartFile文件给远程接口

参考于：https://blog.csdn.net/weixin_30357231/article/details/97925465

方法头：

 public AjaxJson fileUpload(@RequestPart(value = "file") MultipartFile file) throws Exception 

        MultiValueMap request = new LinkedMultiValueMap(1);
        ByteArrayResource is = new ByteArrayResource(file.getBytes()) {
            @Override
            public String getFilename() {
                return file.getOriginalFilename();
            }
        };
        request.add("file", is);

        RestTemplate restTemplate = new RestTemplate();
        AjaxJson ajaxJson = null;
        try {
            ajaxJson = restTemplate.postForObject(url, request, AjaxJson.class);
        } catch (RestClientException e) {
            logger.error("文件上传异常");
            e.printStackTrace();
            return AjaxJson.returnExceptionInfo("文件上传异常");
        }