fancyFunction.groovy

    def dataSource    

    String fancyFunction(String jsonInput) {
        String result = ''

        Clob jsonInput = dataSource.getConnection().createClob()
        clob.setString(1, jsonInput)

        try {
            new Sql(dataSource).call("{? = call pkg.fancy_procedure_input_output_clob(in_json => ?)}",
                    [Sql.CLOB,
                     clob])
                    { jsonOutput -> result = jsonOutput?.characterStream?.text }
        } catch (SQLException ex) {
            log.error('Error during executing fancy procedure: ', ex)
        }

        return result
    }