code: public static <K, V> ImmutableMap<K, V> loadMap(final File file,
        final Function<String, K> keyFunction, final Function<String, V> valueFunction)
        throws IOException {
      return loadMap(Files.asCharSource(file, Charsets.UTF_8), keyFunction, valueFunction);
    }
docs: Reads an {@link ImmutableMap} from a {@link File}, where each line is a key, a tab
  character ("\t"), and a value. Blank lines and lines beginning with "#" are ignored.