val list = List("""{"name":"abc","salary":"2000","id":"1","timeStamp" : "1528725600000"}""")

"com.typesafe.play" %% "play-json" % "2.6.9"

list.map(x => Json.parse(x).as[Map[String,String]])
  .sortBy(y => y.getOrElse("timeStamp","0").toLong)