protected function registerPsr(array $composer_config) {
    $psr0 = $psr4 = array();
    if (!empty($composer_config['psr-0'])) {
      $psr0 = (array) $composer_config['psr-0'];
    }
    if (!empty($composer_config['psr-4'])) {
      $psr4 = (array) $composer_config['psr-4'];
    }
    if (empty($psr4) && empty($psr0)) {
      return;
    }
    $this->loader->setPsrClassMap(array(
      'psr-0' => $psr0,
      'psr-4' => $psr4,
    ));
    $this->loader->registerPsr($this->classLoader);
  }