How to convert unix timestamp to date in Spark

I have a data frame with a column of unix timestamp(eg.1435655706000), and I want to convert it to data with format 'yyyy-MM-DD', I've tried nscala-time but it doesn't work.

val time_col = sqlc.sql("select ts from mr").map(_(0).toString.toDateTime)
time_col.collect().foreach(println)

and I got error: java.lang.IllegalArgumentException: Invalid format: "1435655706000" is malformed at "6000"

Here it is using Scala DataFrame functions: from_unixtime and to_date

// NOTE: divide by 1000 required if milliseconds
// e.g. 1446846655609 -> 2015-11-06 21:50:55 -> 2015-11-06 
mr.select(to_date(from_unixtime($"ts" / 1000))) 

Since spark1.5 , there is a builtin UDF for doing that.

val df = sqlContext.sql("select from_unixtime(ts,'YYYY-MM-dd') as `ts` from mr")

Please check Spark 1.5.2 API Doc for more info.