[英]Scala to JSON in Play Framework 2.1
我正試圖在2.1RC Play Framework中將Scala轉換為JSON。
我可以執行以下操作並獲取JSON:
import play.api.libs.json._
val a1=Map("val1"->"a", "val2"->"b")
Json.toJSon(a1)
因為a1只是Map [String,String]才能正常工作。
但是,如果我有更復雜的東西,比如我有Map [String,Object],那就不行了:
val a = Map("val1" -> "xxx", "val2"-> List("a", "b", "c"))
Json.toJSon(a1)
>>> error: No Json deserializer found for type scala.collection.immutable.Map[String,Object]
我發現我可以做以下事情:
val a2 = Map("val1" -> Json.toJson("a"), "val2" -> Json.toJson(List("a", "b", "c")))
Json.toJson(a2)
這很有效。
但是我怎么能以一般的方式做到這一點? 我以為我可以做以下事情:
a.map{ case(k,v)=> (k, Json.toJson(v) )}
>>> error: No Json deserializer found for type Object
但我仍然得到一個錯誤,它無法反序列化
附加信息:
Json.toJson可以將Map [String,String]轉換為JsValue:
scala> val b = Map( "1" -> "A", "2" -> "B", "3" -> "C", "4" -> "D" )
b: scala.collection.immutable.Map[String,String] = Map(1 -> A, 2 -> B, 3 -> C, 4 -> D)
scala> Json.toJson(b)
res31: play.api.libs.json.JsValue = {"1":"A","2":"B","3":"C","4":"D"}
但是,它無法嘗試轉換Map [String,Object]:
scala> a
res34: scala.collection.immutable.Map[String,Object] = Map(val1 -> xxx, val2 -> List(a, b, c))
scala> Json.toJson(a)
<console>:12: error: No Json deserializer found for type scala.collection.immutable.Map[String,Object]. Try to implement an implicit Writes or Format for this type.
Json.toJson(a)
使用此Play Framework頁面中的'提示'將Scala轉換為Json,我找到了以下內容( http://www.playframework.org/documentation/2.0.1/ScalaJson ):
如果不是Map [String,Object],而是Map [String,JsValue],那么Json.toJson()將起作用:
scala> val c = Map("aa" -> Json.toJson("xxxx"), "bb" -> Json.toJson( List("11", "22", "33") ) )
c: scala.collection.immutable.Map[String,play.api.libs.json.JsValue] = Map(aa -> "xxxx", bb -> ["11","22","33"])
scala> Json.toJson(c)
res36: play.api.libs.json.JsValue = {"aa":"xxxx","bb":["11","22","33"]}
所以,我想要的是,給定一個Map [String,Object],我知道Object值最初都是String或List [String]類型,如何將函數Json.toJson()應用於all map中的值並獲取Map [String,JsValue]。
我還發現我可以過濾掉那些純粹是字符串的值和那些類型為List [String]的值:
scala> val a1 = a.filter({case(k,v) => v.isInstanceOf[String]})
a1: scala.collection.immutable.Map[String,Object] = Map(val1 -> xxx)
scala> val a2 = a.filter({case(k,v) => v.isInstanceOf[List[String]]})
<console>:11: warning: non-variable type argument String in type List[String] is unchecked since it is eliminated by erasure
val a2 = a.filter({case(k,v) => v.isInstanceOf[List[String]]})
^
a2: scala.collection.immutable.Map[String,Object] = Map(val2 -> List(a, b, c))
List [String]過濾會發出警告,但似乎給出了我想要的答案。 如果可以應用兩個過濾器,然后在結果的值上使用Json.toJson(),並且結果合並,也許這會起作用?
但過濾后的結果仍然是Map [String,Object]類型,這會導致問題:
scala> Json.toJson(a1)
<console>:13: error: No Json deserializer found for type scala.collection.immutable.Map[String,Object]. Try to implement an implicit Writes or Format for this type.
Json.toJson(a1)
Play 2.1 JSON API不為Type Map[String, Ojbect]
提供序列化程序。
定義特定類型的case class
和Format
,而不是Map[String, Object]
:
// { "val1" : "xxx", "val2" : ["a", "b", "c"] }
case class Hoge(val1: String, val2: List[String])
implicit val hogeFormat = Json.format[Hoge]
如果您不想創建案例類。 以下代碼為Map [String,Object]提供了JSON序列化器/反序列化器:
implicit val objectMapFormat = new Format[Map[String, Object]] {
def writes(map: Map[String, Object]): JsValue =
Json.obj(
"val1" -> map("val1").asInstanceOf[String],
"val2" -> map("val2").asInstanceOf[List[String]]
)
def reads(jv: JsValue): JsResult[Map[String, Object]] =
JsSuccess(Map("val1" -> (jv \ "val1").as[String], "val2" -> (jv \ "val2").as[List[String]]))
}
import play.api.libs.json._
import play.api.libs.json.Reads._
import play.api.libs.json.Json.JsValueWrapper
implicit val objectMapFormat = new Format[Map[String, Object]] {
def writes(map: Map[String, Object]): JsValue =
Json.obj(map.map{case (s, o) =>
val ret:(String, JsValueWrapper) = o match {
case _:String => s -> JsString(o.asInstanceOf[String])
case _ => s -> JsArray(o.asInstanceOf[List[String]].map(JsString(_)))
}
ret
}.toSeq:_*)
def reads(jv: JsValue): JsResult[Map[String, Object]] =
JsSuccess(jv.as[Map[String, JsValue]].map{case (k, v) =>
k -> (v match {
case s:JsString => s.as[String]
case l => l.as[List[String]]
})
})
}
示例代碼:
val jv = Json.toJson(Map("val1" -> "xxx", "val2" -> List("a", "b", "c"), "val3" -> "sss", "val4" -> List("d", "e", "f")))
println(jv)
val jr = Json.fromJson[Map[String, Object]](jv)
println(jr.get)
輸出:
> {"val1":"xxx","val2":["a","b","c"],"val3":"sss","val4":["d","e","f"]}
> Map(val1 -> xxx, val2 -> List(a, b, c), val3 -> sss, val4 -> List(d, e, f))
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