code: protected HttpURLConnection openConnection(String path, String query)
        throws IOException {
      try {
        final URL url = new URI("http", null, nnAddr.getAddress().getHostAddress(),
            nnAddr.getPort(), path, query, null).toURL();
        if (LOG.isTraceEnabled()) {
          LOG.trace("url=" + url);
        }
        return (HttpURLConnection)url.openConnection();
      } catch (URISyntaxException e) {
        throw (IOException)new IOException().initCause(e);
      }
    }
docs: Open an HTTP connection to the namenode to read file data and metadata.
  @param path The path component of the URL
  @param query The query component of the URL