public static String keyOfIdGenerator(Class<?> clazz){
  try {
    return ID_GENERATOR_KEY_CACHE.get(clazz);
  }
 catch (  ExecutionException e) {
    throw new KeyException(e);
  }
}

public static String keyOfIdGenerator ( Class < ? > clazz ) { try { return ID_GENERATOR_KEY_CACHE . get ( clazz ) ; } catch ( ExecutionException e ) { throw new KeyException ( e ) ; } }
the key of id generator
