Tunneling MultipartFile

Question

I have a spring controller that accepts a class named FileUploadBean on POST. The controller method looks like that:

First Controller:

@RequestMapping(value = "/upload", method = RequestMethod.POST)
@ResponseBody
public ResponseEntity<byte[]> uploadFile(final FileUploadBean fileUploadBean) throws IOException {
   // Some code that works fine here
} 

One of the FileUploadBean properties is of type MultipartFile.

Now, I'm trying to add some sort of wrapper controller (that will run on another server) that also accepts FileUploadBean and just forwards the request to the first controller:

Second (wrapper) Controller:

@RequestMapping(value="/upload", method = RequestMethod.POST)
@ResponseBody
public ResponseEntity<byte[]> uploadImage(final FileUploadBean fileUploadBean) throws IOException {
  ResponseEntity<byte[]> response = restTemplate.postForEntity([first controller url here], fileUploadBean, byte[].class);
  return response;
}

When I'm sending the request to the first controller I get:

org.springframework.http.converter.HttpMessageNotWritableException:

Could not write JSON: No serializer found for class java.io.FileDescriptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.outbrain.images.beans.FileUploadBean["file"]->org.springframework.web.multipart.commons.CommonsMultipartFile["fileItem"]->org.apache.commons.fileupload.disk.DiskFileItem["inputStream"]->java.io.FileInputStream["fd"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class java.io.FileDescriptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.outbrain.images.beans.FileUploadBean["file"]->org.springframework.web.multipart.commons.CommonsMultipartFile["fileItem"]->org.apache.commons.fileupload.disk.DiskFileItem["inputStream"]->java.io.FileInputStream["fd"]) at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal

How can I make this request work?

Answer 1

Well, after some struggling this is how I solved it. That's what I did in the second controller:

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public @ResponseBody
ResponseEntity<byte[]> uploadImage(final FileUploadBean fileUploadBean) throws Exception {
  File file = null;
  try {
    final MultiValueMap<String, Object> requestParts = new LinkedMultiValueMap<>();

    final String tmpImageFileName = IMAGE_TMP_DIR + fileUploadBean.getFile().getOriginalFilename();
    file = new File(tmpImageFileName);
    fileUploadBean.getFile().transferTo(file);
    requestParts.add("file", new FileSystemResource(tmpImageFileName));

    HttpHeaders headers = new HttpHeaders();
    headers.set("Content-Type", "multipart/form-data"); // Sending it like the client-form sends it

    ResponseEntity<byte[]> response = restTemplate.exchange(ImageUrlUtils.getUploadUrl(), HttpMethod.POST, new HttpEntity<>(requestParts, headers),
      byte[].class);

    return new ResponseEntity<>(response.getBody(), response.getStatusCode());
  } catch (Exception ex) {
    return new ResponseEntity<>((ex.getMessage).getBytes("UTF-8"),
      HttpStatus.INTERNAL_SERVER_ERROR);
  } finally {
    if (file != null && file.exists()) {
      file.delete();
    }
  }
}