JSON2XML.scala

import scala.xml._
import scala.util.parsing.json.JSON

/**
 * The XML2JSON object will transform a string in json format to
 * a NodeSeq object.
 */
object JSON2XML {

  def apply(input:String):NodeSeq = {
    JSON.parse(input) match {
      case Some(json) => toXML(json)
      case _ => Seq.empty
    }
  }

  private def toXML(json:Any):NodeSeq = json match {
    case (k:String, v)  if !v.isInstanceOf[List[_]] =>
      toElem(k, Text(v.toString))
    case (k:String, Nil) => toElem(k, Nil:_*)
    case (k:String, v@(_,_)::_) =>
      toElem(k, v.flatMap(toXML(_)):_*)
    case (k:String, v:List[_]) => // array
      for(_v <- v) yield toElem(k, toXML(_v):_* )
    case l:List[_] => l.flatMap(toXML(_))
    case v => Text(v.toString)
  }

  private implicit def toSeq(n:Node):NodeSeq=List(n)

  private def toElem(label:String, child:Node*) =
      Elem(null, label, Null, TopScope, child:_*)
}

object JSON2XMLTest extends Application {
  val json="""                                                                  
{                                                                               
  "Image": {                                                                    
    "Width":  800,                                                              
    "Height": 600,                                                              
    "Title":  "View from 15th Floor",                                           
    "Thumbnail": {                                                              
      "Url":    "http://www.example.com/image/481989943",                       
      "Height": 125,                                                            
      "Width":  "100"                                                           
    },                                                                          
    "IDs": [116, 943, 234, 38793]                                               
  }                                                                             
}                                                                               
"""; // from http://tools.ietf.org/html/rfc4627                                 

  // Changing numberParser.                                                     
  // JSON#perThreadNumberParser has been introduces since 2.7.2.                
  // JSON.perThreadNumberParser = {_.toInt}                                     

  println(new PrettyPrinter(80, 2).formatNodes(JSON2XML(json)))
}