public class MultipartRequest

// File: MultipartClientSample.java
MultipartRequest request = new MultipartRequest();
request.setUrl(url);
request.addData("myFileName", fullPathToFile, "text/plain");
NetworkManager.getInstance().addToQueue(request);

// File: UploadServlet.java
@WebServlet(name = "UploadServlet", urlPatterns = {"/upload"})
@MultipartConfig(fileSizeThreshold = 1024 * 1024 * 100, // 10 MB
        maxFileSize = 1024 * 1024 * 150, // 50 MB
        maxRequestSize = 1024 * 1024 * 200)      // 100 MB
public class UploadServlet extends HttpServlet {
@Override
    public void doPost(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        Collection parts = req.getParts();
        Part data = parts.iterator().next();
        try(InputStream is = data.getInputStream()) {}
            // store or do something with the input stream
        }
    }
}

public void pictureUpload(final Callback resultURL) {
    String picture = Capture.capturePhoto(1024, -1);
    if(picture!=null){
        String filestack = "https://www.filestackapi.com/api/store/S3?key=MY_KEY&filename=myPicture.jpg";
        MultipartRequest request = new MultipartRequest() {
           protected void readResponse(InputStream input) throws IOException  {
              JSONParser jp = new JSONParser();
              Map result = jp.parseJSON(new InputStreamReader(input, "UTF-8"));
              String url = (String)result.get("url");
              if(url == null) {
                 resultURL.onError(null, null, 1, result.toString());
                 return;
              }
              resultURL.onSucess(url);
           }
        };
        request.setUrl(filestack);
        try {
            request.addData("fileUpload", picture, "image/jpeg");
            request.setFilename("fileUpload", "myPicture.jpg");
            NetworkManager.getInstance().addToQueue(request);
        } catch(IOException err) {
            err.printStackTrace();
        }
    }
}