default void transform(Column[] columns, ColumnBuilder timesBuilder, ColumnBuilder valuesBuilder)
      throws Exception {
    throw new UnsupportedOperationException();
  }
This method is mainly used to customize UDTF. In this method, the user can do the following
things:

<ul>
  <li>Use UDFParameters to get the time series paths and parse key-value pair attributes
      entered by the user.
  <li>Set the strategy to access the original data and set the output data type in
      UDTFConfigurations.
  <li>Create resources, such as establishing external connections, opening files, etc.
</ul>

<p>This method is called after the UDTF is instantiated and before the beginning of the
transformation process.

@param parameters used to parse the input parameters entered by the user
@param configurations used to set the required properties in the UDTF
@throws Exception the user can throw errors if necessary
iotdb-api/udf-api/src/main/java/org/apache/iotdb/udf/api/UDTF.java