Polymorphic lift-json deserialization in a composed class

Yes, you need to use type hints for sum types like Geometry. Here's one example:

implicit val formats = DefaultFormats.withHints(ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon])))val r = Request("test", LineString(List(Point(100.0, 0.0), Point(101.0, 1.0))))Serialization.write(r){"name":"test","geometry":{  "jsonClass":"LineString",  "coordinates":[{"jsonClass":"Point","coordinates":{"_1$mcD$sp":100.0,"_2$mcD$sp":0.0}},{"jsonClass":"Point","coordinates":{"_1$mcD$sp":101.0,"_2$mcD$sp":1.0}}]}}

Not quite what you wanted. Since you want to change the default serialization scheme for Points, you need to provide a custom serializer for that type.

class PointSerializer extends Serializer[Point] {  private val Class = classOf[Point]  def deserialize(implicit format: Formats) = {    case (TypeInfo(Class, _), json) => json match {      case JArray(JDouble(x) :: JDouble(y) :: Nil) => Point(x, y)      case x => throw new MappingException("Can't convert " + x + " to Point")    }  }  def serialize(implicit format: Formats) = {    case p: Point => JArray(JDouble(p.coordinates._1) :: JDouble(p.coordinates._2) :: Nil)  }}// Configure itimplicit val formats = DefaultFormats.withHints(ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon]))) + new PointSerializerSerialization.write(r){  "name":"test",  "geometry":{    "jsonClass":"LineString",    "coordinates":[[100.0,0.0],[101.0,1.0]]  }}

Better, but you need one more configuration if you need to change the default field named as 'jsonClass' to 'type':

implicit val formats = new DefaultFormats {   override val typeHintFieldName = "type"   override val typeHints = ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon]))} + new PointSerializerSerialization.write(r){  "name":"test",  "geometry":{    "type":"LineString",    "coordinates":[[100.0,0.0],[101.0,1.0]]  }}