public InputStream downloadFile(final String url, final Map<String, ?> form,
        final Map<String, String> header) throws IOException {
        Request.Builder requestBuilder = buildRequestBuilder(url, form, HTTPMethod.GET);
        addHeader(requestBuilder, header);

        Request request = requestBuilder.build();
        try (Response response = httpClient
                .newCall(request)
                .execute()) {
            if (response.isSuccessful()) {
                ResponseBody body = response.body();
                return Objects.isNull(body) ? null : body.byteStream();
            }
            return null;
        }
    }
download file.

@param url    request url
@param form   request data
@param header header
@return InputStream
@throws IOException IOException
shenyu-admin/src/main/java/org/apache/shenyu/admin/utils/HttpUtils.java