@SuppressWarnings("unchecked")
private void writePart(String name, HttpEntity partEntity, OutputStream os) throws IOException {
Object partBody = partEntity.getBody();
Class<?> partType = partBody.getClass();
HttpHeaders partHeaders = partEntity.getHeaders();
MediaType partContentType = partHeaders.getContentType();
for (HttpMessageConverter messageConverter : partConverters) {
if (messageConverter.canWrite(partType, partContentType)) {
HttpOutputMessage multipartOutputMessage = new MultipartHttpOutputMessage(os);
multipartOutputMessage.getHeaders().setContentDispositionFormData(name, getFilename(partBody));
if (!partHeaders.isEmpty()) {