code: public static String relativize(File baseDir, File file) {
          try {
              baseDir = baseDir.getCanonicalFile();
              file = file.getCanonicalFile();
  
              return baseDir.toURI().relativize(file.toURI()).getPath();
          } catch (IOException e) {
              throw new DockerClientException(e.getMessage(), e);
          }
      }
docs: Return the relative path. Path elements are separated with / char.
  
  @param baseDir
  a parent directory of {@code file}
  @param file
  the file to get the relative path
  @return the relative path