code: public static String makeAbsolute(String path, String rootPath) {
      if (!isAbsolute(path)) {
        path = rootPath + "/" + path;
      }
      return collapseDots(path);
    }
docs: Converts the given path into an absolute one. This prepends the given
  rootPath and removes all .'s from the path. If an absolute path is given,
  it will not be prefixed.
  
  <p>Unlike File.getAbsolutePath(), this function does remove .'s from the
  path and unlike File.getCanonicalPath(), this function does not resolve
  symlinks and does not use filesystem calls.</p>
  
  @param rootPath The path to prefix to path if path is not already absolute.
  @param path The path to make absolute.
  @return The path made absolute.