RestTemplate上傳文件並獲取返回的文件流

    private InputStream convertPdf(MultipartFile multipartFile) throws IOException {
        Assert.notNull(multipartFile, "MultipartFile 為 null");
        File file = new File(Objects.requireNonNull(multipartFile.getOriginalFilename()));
        FileUtils.copyInputStreamToFile(multipartFile.getInputStream(), file);
        FileSystemResource resource = new FileSystemResource(file);
        MultiValueMap<String, Object> params = new LinkedMultiValueMap();
        params.add("file", resource);
        params.add("dstFormat", "pdf");
        RestTemplate restTemplate = new RestTemplate();
        ResponseEntity<Resource> entity = restTemplate.postForEntity(convertPdfUrl, params, Resource.class);
        InputStream ins = Objects.requireNonNull(entity.getBody()).getInputStream();
        return ins;
    }