val todaydate = LocalDate.now().toString()
println(todaydate)  // o/p: 2016-12-10

val todayrec_cutoff = todaydate + (" ") + df.col("colname")

2016-12-10 05:00
2016-12-10 22:30

import java.time.LocalDate

val df = Seq(("05:00"), ("22:30")).toDF("time")
df.show
val todaydate = LocalDate.now().toString()
val df2 = df.select(concat(lit(todaydate+ " "),df.col("time"))).toDF("datetime");
df2.show

+----------------+
|        datetime|
+----------------+
|2016-12-10 05:00|
|2016-12-10 22:30|
+----------------+

val prefixVal= "PrefixArkay " //variable string
val prefixVal= " PostfixArkay"

//Prefix
val finalPreDF = ipDF.withColumn("EMP", concat(lit(prefix),empDF.col("EMP")) )
println("finalPreDF.show-> " + finalPreDF.show())

//Output will be as below
+-------------------+
|                EMP|
+-------------------+
|PrefixArkay DineshS|
|+------------------+


val finalPostDF = ipDF.withColumn("EMP", concat(empDF.col("EMP"),lit(prefix)) )
println("finalPostDF.show-> " + finalPostDF .show())

//Output will be as below
+--------------------+
|                 EMP|
+--------------------+
|DineshS PostfixArkay|
|+-------------------+