public void addFunctionAndClass(Model model, String functionName, Class<?> clazz) {
    functionToClassMap.get(model).put(functionName.toUpperCase(), clazz);
  }
maintain a map for creating instance, model -> functionName -> class
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/udf/UDFTable.java