code: @Override
      public InputStream getInputStream(String relativePath) throws IOException {
          File file = new File(folder, relativePath);
          if( !file.exists() )                      {
              String msg = String.format("Can't find any file with relative path = `%s` in folder: `%s`",
                                         relativePath, folder.getAbsolutePath());
              throw new IllegalArgumentException(msg);
          }
          return new FileInputStream(file);
      }
docs: //////////////////////////////////////////////////////////////////////////////////////////////////////////