code: public static DDFManager get(EngineType engineType) throws DDFException {
      if (engineType == null) {
        engineType = EngineType.fromString(ConfigConstant.ENGINE_NAME_DEFAULT.toString());
      }
  
      String className = Config.getValue(engineType.name(), ConfigConstant.FIELD_DDF_MANAGER);
      if (Strings.isNullOrEmpty(className)) {
        throw new DDFException("ERROR: When initializaing ddfmanager, class " +
                className + " not found");
      }
  
      try {
        DDFManager manager = (DDFManager) Class.forName(className).newInstance();
        if (manager == null) {
          throw new DDFException("ERROR: Initializaing manager fail.");
        }
        return manager;
  
      } catch (Exception e) {
        // throw new DDFException("Cannot get DDFManager for engine " + engineName, e);
        throw new DDFException(
            "Cannot get DDFManager for engine " + engineType.name() + " " +
                    "classname " + className + " " + e.getMessage());
  
      }
    }
docs: Returns a new instance of {@link DDFManager} for the given engine type
  
  @param engineType
  @return
  @throws Exception