Question

我正在尝试使用Lift-Json自动将json对象反序列化为scala类，其中一个坐标类用于存储GeoJson信息。

case class Request(name:String, geometry:Geometry)

sealed abstract class Geometry

case class Point(coordinates:(Double,Double)) extends Geometry
case class LineString(coordinates:List[Point]) extends Geometry
case class Polygon(coordinates:List[LineString]) extends Geometry

我想反序列化一个像这样的json字符串：

{
name:"test",
geometry:{
   "type": "LineString",
   "coordinates": [ [100.0, 0.0], [101.0, 1.0] ]
  }
}

在Geometry字段中使用正确的LineString运行时类进入Request case类。我想我应该使用TypeHint但是怎么样？这是正确的方法还是应该创建三个不同的Request（RequestPoint，RequestLineString和RequestPolygon）？这将是反序列化的Scala代码：

val json = parse(message)
json.extract[Request]

Answer 1

是的，您需要对像Geometry这样的和类型使用类型提示。这是一个例子：

implicit val formats = DefaultFormats.withHints(ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon])))

val r = Request("test", LineString(List(Point(100.0, 0.0), Point(101.0, 1.0))))

Serialization.write(r)

{
"name":"test",
"geometry":{
  "jsonClass":"LineString",
  "coordinates":[{"jsonClass":"Point","coordinates":{"_1$mcD$sp":100.0,"_2$mcD$sp":0.0}},{"jsonClass":"Point","coordinates":{"_1$mcD$sp":101.0,"_2$mcD$sp":1.0}}]}
}

不完全是你想要的。由于您要更改Points的默认序列化方案，因此需要为该类型提供自定义序列化程序。

class PointSerializer extends Serializer[Point] {
  private val Class = classOf[Point]

  def deserialize(implicit format: Formats) = {
    case (TypeInfo(Class, _), json) => json match {
      case JArray(JDouble(x) :: JDouble(y) :: Nil) => Point(x, y)
      case x => throw new MappingException("Can't convert " + x + " to Point")
    }
  }

  def serialize(implicit format: Formats) = {
    case p: Point => JArray(JDouble(p.coordinates._1) :: JDouble(p.coordinates._2) :: Nil)
  }
}

// Configure it
implicit val formats = DefaultFormats.withHints(ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon]))) + new PointSerializer

Serialization.write(r)

{
  "name":"test",
  "geometry":{
    "jsonClass":"LineString",
    "coordinates":[[100.0,0.0],[101.0,1.0]]
  }
}

更好，但如果您需要将名为'jsonClass'的默认字段更改为'type'，则还需要一个配置：

implicit val formats = new DefaultFormats { 
  override val typeHintFieldName = "type" 
  override val typeHints = ShortTypeHints(List(classOf[Point], classOf[LineString], classOf[Polygon]))
} + new PointSerializer

Serialization.write(r)

{
  "name":"test",
  "geometry":{
    "type":"LineString",
    "coordinates":[[100.0,0.0],[101.0,1.0]]
  }
}

组合类中的多态lift-json反序列化

1 个答案: