code: public ImageUrlMap getImageUrls(List<ImageUrl> requestUrls) throws SmartsheetException
      {
          Util.throwIfNull(requestUrls);
  
          HttpRequest request;
          request = createHttpRequest(smartsheet.getBaseURI().resolve("imageurls"), HttpMethod.POST);
  
          ByteArrayOutputStream baos = new ByteArrayOutputStream();
          this.smartsheet.getJsonSerializer().serialize(requestUrls, baos);
          HttpEntity entity = new HttpEntity();
          entity.setContentType("application/json");
          entity.setContent(new ByteArrayInputStream(baos.toByteArray()));
          entity.setContentLength(baos.size());
          request.setEntity(entity);
  
          HttpResponse response = this.smartsheet.getHttpClient().request(request);
  
          ImageUrlMap obj = null;
  
          switch (response.getStatusCode()) {
              case 200:
                  try {
                      obj = this.smartsheet.getJsonSerializer().deserialize(ImageUrlMap.class,
                              response.getEntity().getContent());
                  } catch (JsonParseException e) {
                      throw new SmartsheetException(e);
                  } catch (JsonMappingException e) {
                      throw new SmartsheetException(e);
                  } catch (IOException e) {
                      throw new SmartsheetException(e);
                  }
                  break;
              default:
                  handleError(response);
          }
          smartsheet.getHttpClient().releaseConnection();
          return obj;
      }
docs: Gets URLS that can be used to retieve the specified cell images.
  
  It mirrors to the following Smartsheet REST API method: POST /imageurls
  
  @param requestUrls array of requested Images ans sizes.
  @return the ImageUrlMap object (note that if there is no such resource, this method will throw
  ResourceNotFoundException rather than returning null).
  @throws JSONSerializerException
  @throws IllegalArgumentException if any argument is null or empty string
  @throws InvalidRequestException if there is any problem with the REST API request
  @throws AuthorizationException if there is any problem with  the REST API authorization (access token)
  @throws ResourceNotFoundException if the resource cannot be found
  @throws ServiceUnavailableException if the REST API service is not available (possibly due to rate limiting)
  @throws SmartsheetException if there is any other error during the operation