Scala为Map播放Json格式[Locae，String]

Question

我有类型的对象

Map[java.util.Locale, String] 

如何对此进行Json写入/读取？我已经研究了其他几个问题，但自己无法想出解决方案。我得到了（但还没有测试）Locale 的一些东西

implicit val localeReads: Reads[Locale] = new Reads[Locale] {
  def reads(json: JsValue): JsResult[Locale] =
    json match {
      case JsString(langString) => JsSuccess(new Locale(langString))
      case _ => JsError("Locale Language String Expected")
    }
}
implicit val localeWrites: Writes[Locale] = new Writes[Locale] {
  def writes(locale: Locale) = JsString(locale.toString)
}

然后我如何在中使用它

implicit val myMapReads: Reads[Map[Locale, String]] = ???
implicit val myMapWrites: Writes[Map[Locale, String]] = ???

Answer 1

这应该有效：

implicit val localeReads: Reads[Locale] = new Reads[Locale] {
  def reads(json: JsValue): JsResult[Locale] =
    json match {
      case JsString(langString) => JsSuccess(new Locale(langString))
      case _ => JsError("Locale Language String Expected")
    }
}
implicit val localeWrites: Writes[Locale] = new Writes[Locale] {
  def writes(locale: Locale) = JsString(locale.toString)
}
implicit val myMapWrites: Writes[Map[Locale, String]] = new Writes[Map[Locale, String]] {
  override def writes(o: Map[Locale, String]): JsValue = Json.toJson(o)
}
implicit val myMapRead: Reads[Map[Locale, String]] = new Reads[Map[Locale, String]] {
  override def reads(json: JsValue): JsResult[Map[Locale, String]] = JsSuccess {
    json.as[JsObject].value.map {
      case (k, v) => (new Locale(k), v.as[String])
    }.toMap
  }
}

基本上play已经知道如何将Locale转换为json，因为您提供了Writes，所以只需调用toJson就可以了。

对于Reads，它有点复杂，并且您必须进行映射，.value返回一个Map[String, JsValue]，其中第一个表示Locale对象，第二个表示简单字符串，因此调用as[String]已经可以得到您想要的内容。

请注意，我已经将所有内容都封装在JsSuccess中，但您可能会认为您得到的json无法转换为JsObject，应用try/catch，并决定是返回成功还是失败。

Answer 2

如果K串行化为JsString，以下是一个将为您创建Format[K,V]的函数：

/** Play Json only supports Map[String,V]. This function creates a format for Map[K,V]. The type K should produce a JsString.
 * Otherwise the serialisation will fail. Which should be good enough since in valid json keys can only be strings. 
*/
def mapFormat[K, V](implicit fk: Format[K], fv: Format[V]): Format[Map[K, V]] = 
  new OFormat[Map[K, V]] {
    override def writes(o: Map[K, V]): JsObject = {
      val stringMap = o.map { case (k, v) => (Json.toJson[K](k).as[JsString].value, v) }
      Json.toJson(stringMap).as[JsObject]
    }
    override def reads(json: JsValue): JsResult[Map[K, V]] = {
      for {
        stringMap <- Json.fromJson[Map[String, V]](json)
        _         <- Json.fromJson[Set[K]](Json.toJson(stringMap.keySet))
      } yield stringMap.map { case (k, v) => (Json.fromJson[K](JsString(k)).get, v) }
    }
  }