code: public BoxRequestsFile.DownloadFile getDownloadUrlRequest(File target, String url) throws IOException{
          if (!target.exists()){
              throw new FileNotFoundException();
          }
          BoxRequestsFile.DownloadFile request = new BoxRequestsFile.DownloadFile(target, url,mSession);
          return request;
      }
docs: Gets a request that downloads a given asset from the url to a target file
  This is used to download miscellaneous url assets for instance from the representations endpoint.
  @param target    target file to download to, target can be either a directory or a file
  @param url    url of the asset to download
  @return  request to download a file to a target file
  @throws IOException throws FileNotFoundException if target file does not exist.