使用方法如下：

val df = List((1,2,3,5,"a"),(4,2,3,1,"a"),(1,20,3,1,"a"),(1,22,22,2,"a")).toDF("mycol1","mycol2","mycol3","mycol4","mycol5")

//list all your columns among which you want to find the max value
    val colGroup = List(df("mycol1"),df("mycol2"),df("mycol3"),df("mycol4"))

//list column value -> column name of the columns among which you want to find max value column NAME
    val colGroupMap = List(df("mycol1"),lit("mycol1"),
df("mycol2"),lit("mycol2"),
df("mycol3"),lit("mycol3"),
df("mycol4"),lit("mycol4"))

    var maxcol =  udf((colVal: Map[Int,String]) => {
      colVal.max._2  //you can easily find the column name of the max column value
    })

    df.withColumn("maxColValue",greatest(colGroup:_*)).withColumn("maxColVal_Name",maxcol(map(colGroupMap:_*))).show(false)

    +------+------+------+------+------+-----------+--------------+
    |mycol1|mycol2|mycol3|mycol4|mycol5|maxColValue|maxColVal_Name|
    +------+------+------+------+------+-----------+--------------+
    |1     |2     |3     |5     |a     |5          |mycol4        |
    |4     |2     |3     |1     |a     |4          |mycol1        |
    |1     |20    |3     |1     |a     |20         |mycol2        |
    |1     |22    |22    |2     |a     |22         |mycol3        |
    +------+------+------+------+------+-----------+--------------+