这是一个Foo
伴生对象的手动实现:
implicit val barFmt = Json.format[Bar]
implicit val bazFmt = Json.format[Baz]
object Foo {
def unapply(foo: Foo): Option[(String, JsValue)] = {
val (prod: Product, sub) = foo match {
case b: Bar => (b, Json.toJson(b)(barFmt))
case b: Baz => (b, Json.toJson(b)(bazFmt))
}
Some(prod.productPrefix -> sub)
}
def apply(`class`: String, data: JsValue): Foo = {
(`class` match {
case "Bar" => Json.fromJson[Bar](data)(barFmt)
case "Baz" => Json.fromJson[Baz](data)(bazFmt)
}).get
}
}
sealed trait Foo
case class Bar(i: Int ) extends Foo
case class Baz(f: Float) extends Foo
implicit val fooFmt = Json.format[Foo]
验证:
val in: Foo = Bar(33)
val js = Json.toJson(in)
println(Json.prettyPrint(js))
val out = Json.fromJson[Foo](js).getOrElse(sys.error("Oh no!"))
assert(in == out)
或者选择直接格式定义:
implicit val fooFmt: Format[Foo] = new Format[Foo] {
def reads(json: JsValue): JsResult[Foo] = json match {
case JsObject(Seq(("class", JsString(name)), ("data", data))) =>
name match {
case "Bar" => Json.fromJson[Bar](data)(barFmt)
case "Baz" => Json.fromJson[Baz](data)(bazFmt)
case _ => JsError(s"Unknown class '$name'")
}
case _ => JsError(s"Unexpected JSON value $json")
}
def writes(foo: Foo): JsValue = {
val (prod: Product, sub) = foo match {
case b: Bar => (b, Json.toJson(b)(barFmt))
case b: Baz => (b, Json.toJson(b)(bazFmt))
}
JsObject(Seq("class" -> JsString(prod.productPrefix), "data" -> sub))
}
}
理想情况下,我希望自动生成apply
和unapply
方法。看起来我需要使用反射或深入研究宏。