如何解析scala中的mutableList作为播放框架2.0上的JSON？

Question

I am working on Play Framework 2.0 and it uses Jerkson to parse JSON strings. I was using it successfully to parse Immutable Lists of strings like so:

Json.parse( jsonStr ).as[ List[String] ]

But this code doesn't work for me when I try

Json.parse( jsonStr ).as[ MutableList[String] ]

Does anyone know how I can do this easily?

Answer 1

Your second line will work as it is in a future version of Play 2.0, thanks to the replacement of seqReads by traversableReads in the current trunk :

implicit def traversableReads[F[_], A](implicit bf: generic.CanBuildFrom[F[_], A, F[A]], ra: Reads[A]) = new Reads[F[A]] {
  def reads(json: JsValue) = json match {
    case JsArray(ts) => {
      val builder = bf()
      for (a <- ts.map(fromJson[A](_))) {
        builder += a
      }
      builder.result()
    }
    case _ => throw new RuntimeException("Collection expected")
  }
}

So if you're willing to build Play from source , or to wait, you're fine. Otherwise you should be able to drop the method above somewhere in your own code to get an appropriate Reads instance in scope, or—even better—just use Alexey Romanov's solution, or—best of all—don't use MutableList .

Answer 2

Eg new MutableList[String]() ++= Json.parse( jsonStr ).as[ List[String] ] (assuming @DanSimon is correct about which MutableList you mean). But the most used mutable list-like collection in Scala is a Buffer which could be obtained as Buffer(Json.parse( jsonStr ).as[ List[String] ] or Json.parse( jsonStr ).as[ List[String] ].toBuffer .