spark dataframe map field to json

方法1：
import org.apache.spark.sql.functions.to_json

countDF.withColumn("mapfield", to_json($"mapfield"))
方法2：
import org.apache.spark.sql.functions.udf

val convert_map_to_json = udf(
  (map: Map[String, Object]) => convertMapToJSON(map).toString
)

countDF.withColumn("mapfield", convert_map_to_json($"mapfield"))