/**
  * Call api endpoint
  *
  * @param verb http-method to use, like: GET, POST, PUT, DELETE, PATCH
  * @param url the api-url to call
  * @return the output of the api-call, can be a JSON-string
  */
 private String call(Verb verb, String url) {
   String urlEnd = url;
   if (!url.startsWith("/")) {
     urlEnd = "/" + url;
   }
   OAuthRequest request = new OAuthRequest(verb, "https://graph.facebook.com/v2.2" + urlEnd);
   request.addHeader("Authorization", "Bearer " + accessTokenString);
   Response response = request.send();
   return response.getBody();
 }
  /*
   * posts an image to the users news feed
   * @param message to show
   * @param image as form data
   * @return the new image id if successful
   */
  public String publishPicture(String msg, Image image, String placeId) throws IOException {
    OAuthRequest request =
        new OAuthRequest(Verb.POST, "https://graph.facebook.com/v2.2/me/photos"); // request node
    request.addHeader("Authorization", "Bearer " + accessTokenString); // authentificate

    // check input to avoid error responses
    if (msg != null && image != null) {
      // facebook requires multipart post structure
      MultipartEntityBuilder builder = MultipartEntityBuilder.create();
      builder.addTextBody("message", msg); // description

      if (placeId != null && !"".equals(placeId)) {
        builder.addTextBody(
            "place", placeId); // add link to FabLab site if property is set in preferences
      }

      // convert image to bytearray and append to multipart
      BufferedImage bimage =
          new BufferedImage(
              image.getWidth(null), image.getHeight(null), BufferedImage.TYPE_INT_ARGB);
      Graphics2D bGr = bimage.createGraphics();
      bGr.drawImage(image, 0, 0, null);
      bGr.dispose();
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      ImageIO.write(bimage, "png", baos);
      builder.addBinaryBody(msg, baos.toByteArray(), ContentType.MULTIPART_FORM_DATA, "test.png");

      // generate multipart byte stream and add to payload of post package
      HttpEntity multipart = builder.build();
      ByteArrayOutputStream multipartOutStream =
          new ByteArrayOutputStream((int) multipart.getContentLength());
      multipart.writeTo(multipartOutStream);
      request.addPayload(multipartOutStream.toByteArray());

      // set header of post package
      Header contentType = multipart.getContentType();
      request.addHeader(contentType.getName(), contentType.getValue());

      // send and response answer
      Response response = request.send();
      return response.getBody();
    } else {
      throw new RuntimeException(CONSTANTS.get(FACEBOOK_MESSAGE_IMG_NEEDED));
    }
  }