具有以下格式的json结构。如何提取col1和col2字段。
root
|-- F1: array (nullable = true)
| |-- element: string (containsNull = true)
|-- F3: array (nullable = true)
| |-- element: struct (containsNull = true)
| | |-- Columns: array (nullable = true)
| | | |-- element: struct (containsNull = true)
| | | | |-- Col1: string (nullable = true)
| | | | |-- Col2: string (nullable = true)