code: public static Collection<GobblinInstancePluginFactory> instantiatePluginsFromSysConfig(Config config)
        throws ClassNotFoundException, InstantiationException, IllegalAccessException {
      String pluginsStr = config.getString(PLUGINS_KEY);
      List<GobblinInstancePluginFactory> plugins = Lists.newArrayList();
      for (String pluginName : Splitter.on(",").split(pluginsStr)) {
        plugins.add(instantiatePluginByAlias(pluginName));
      }
      return plugins;
    }
docs: Parse a collection of {@link GobblinInstancePluginFactory} from the system configuration by reading the key
  {@link #PLUGINS_KEY}.