Parsing an array of json objects to scala objects with pickling

Question

I'm trying to convert an array of JSON objects from a key to an array of objects in Scala...

Here is the code:

case class RoomList(val rooms : Array[Room])
case class Room(val name : String)

val json = "{\"rooms\" : [{\"name\" : \"Test\"}]}"

println(json.unpickle[RoomList])

Here is the exception

Exception in thread "main" java.lang.InstantiationException: [Lhipchat.Room;
  at sun.misc.Unsafe.allocateInstance(Native Method)
    at hipchat.HipChat$HipchatRoomListUnpickler1$2$ScalaArray$u005BhipchatRoom$u005DUnpickler1$2$.unpickle(HipChat.scala:46)
    at hipchat.HipChat$HipchatRoomListUnpickler1$2$.unpickle(HipChat.scala:46)
    at hipchat.HipChat.getRooms(HipChat.scala:46)
    at bot.Bot$.main(Bot.scala:11)
    at bot.Bot.main(Bot.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)    

Here is a RoomList:

val room = new Room("test")
val rooms = Array(room)
val rl = new RoomList(rooms)
println(rl.pickle)

Pickled:

JSONPickle({
  "tpe": "hipchat.RoomList",
  "rooms": {

  }
})

And a pickled Room:

JSONPickle({
  "tpe": "hipchat.Room",
  "name": "test"
})

Answer 1

Yep, you're correct that there was a period of time when scala/pickling had some trouble dealing with certain collection types of objects. Though, it's worth noting that this has been fixed for a little while now.

Given:

case class Room(val name: String)
case class RoomList(val rooms: Array[Room])

And some RoomList , rl , for example,

val rl = RoomList(Array(Room("foo"), Room("biz"), Room("bang")))

In the REPL, you get:

scala> val p = rl.pickle
p: scala.pickling.json.JSONPickle = 
JSONPickle({
  "tpe": "RoomList",
  "rooms": {
    "elems": [
      {
      "tpe": "Room",
      "name": "foo"
    },
      {
      "tpe": "Room",
      "name": "biz"
    },
      {
      "tpe": "Room",
      "name": "bang"
    }
    ]
  }
})

We can check in the REPL to make sure that the pickled/unpickled version and the original version of rl have the same elements:

scala> rl.pickle.unpickle[RoomList].rooms.sameElements(rl.rooms)
res0: Boolean = true

Added this to the scala/pickling test suite as well :) https://github.com/scala/pickling/blob/2.10.x/core/src/test/scala/pickling/roomlist-object-array.scala

Answer 2

"Collections of non-primitive types are not supported" (yet)

https://github.com/scala/pickling/issues/6

From what I can see, scala.pickling is still very rough around the edges.

Furthermore, the default pickling format JSONPickleFormat requires some meta-data (the tpe field) and I'm guessing won't be parsing arbitrary JSON objects.