code: public static IGroupMappingServiceProvider GetGroupMappingServiceProviderPlugin(Map storm_conf) {
          IGroupMappingServiceProvider gmsp = null;
          try {
              String gmsp_klassName = (String) storm_conf.get(Config.STORM_GROUP_MAPPING_SERVICE_PROVIDER_PLUGIN);
              Class klass = Class.forName(gmsp_klassName);
              gmsp = (IGroupMappingServiceProvider) klass.newInstance();
              gmsp.prepare(storm_conf);
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
          return gmsp;
      }
docs: Construct a group mapping service provider plugin
  
  @param conf storm configuration
  @return the plugin