使用json4s将嵌套的序列化json提取到Scala中的case类中

Question

我试图用Scala中的json4s解析以下Json，但我不能因为嵌套结构：

[
 {
    "body":"8",
    "start":29,
    "value":{
        "value":8,
        "type":"value"
        },
    "end":30,
    "dim":"number",
    "latent":false
 },
 {
    "body":"2",
    "start":42,
    "value":{
        "value":2,
        "type":"value"
        },
    "end":43,
    "dim":"number",
    "latent":false
 }
]

使用以下代码，我只能提取第一个case类，但不提取嵌套类：

println(stdout)
val obs = parse(stdout.toString())
val obs2 = parse(stdout.toString()).extract[DucklingList]
println(obs2.list)

以下是上述输出：

[0m[[0minfo[0m] [0m[{"body":"8","start":29,"value":{"value":8,"type":"value"},"end":30,"dim":"number","latent":false},{"body":"2","start":42,"value":{"value":2,"type":"value"},"end":43,"dim":"number","latent":false}][0m
[0m[[0minfo[0m] [0mList(JObject(List((body,JString(8)), (start,JInt(29)), (value,JObject(List((value,JInt(8)), (type,JString(value))))), (end,JInt(30)), (dim,JString(number)), (latent,JBool(false)))), JObject(List((body,JString(2)), (start,JInt(42)), (value,JObject(List((value,JInt(2)), (type,JString(value))))), (end,JInt(43)), (dim,JString(number)), (latent,JBool(false)))))[0m
[0m[[0minfo[0m] [0mJObject(List((value,JInt(8)), (type,JString(value))))[0m
[0m[[0minfo[0m] [0mDucklingList(List(JObject(List((body,JString(8)), (start,JInt(29)), (value,JObject(List((value,JInt(8)), (type,JString(value))))), (end,JInt(30)), (dim,JString(number)), (latent,JBool(false)))), JObject(List((body,JString(2)), (start,JInt(42)), (value,JObject(List((value,JInt(2)), (type,JString(value))))), (end,JInt(43)), (dim,JString(number)), (latent,JBool(false))))))[0m

我试图使用json4s提取方法使用下面列出的案例类和序列化程序来提取它。

case class DucklingValue(

    value: Int,
    typ: String
  )

  case class DucklingEntity(
    body: String,
    start: Int,
    end: Int,
    value: List[JField],
    dim: String,
    latent: Boolean
  )

  case class DucklingList(
    list: List[JValue]
  )

class DucklingEntitySerializer extends CustomSerializer[DucklingEntity](format => (
  {
    case JObject(
      JField("body", JString(body))
      :: JField("start", JInt(start))
      :: JField("end", JInt(end))
      :: JField("value", JObject(value))
      :: JField("dim", JString(dim))
      :: JField("latent", JBool(latent))
      :: Nil
    ) => DucklingEntity(body, start.toInt, end.toInt, value, dim, latent)
  },
  {
    case duckling_entity: DucklingEntity =>
      JObject(
        JField("body", JString(duckling_entity.body))
        :: JField("start", JInt(duckling_entity.start))
        :: JField("end", JInt(duckling_entity.end))
        :: JField("value", JObject(duckling_entity.value))
        :: JField("dim", JString(duckling_entity.dim))
        :: JField("latent", JBool(duckling_entity.latent))
        :: Nil
      )
  }
))

class DucklingValueSerializer extends CustomSerializer[DucklingValue](format => (
  {
    case JObject(
      JField("value", JInt(value))
      :: JField("type", JString(typ))
      :: Nil
    ) => DucklingValue(value.toInt, typ)
  },
  {
    case duckling_value: DucklingValue =>
      JObject(
        JField("value", JInt(duckling_value.value))
        :: JField("type", JString(duckling_value.typ))
        :: Nil
      )
  }
))


class DucklingListSerializer extends CustomSerializer[DucklingList](format => (
  {
    case JArray(list) => DucklingList(list)
  },
  {
    case duckling_list: DucklingList =>
      JArray(duckling_list.list)
  }
))

如何在Duckling List下提取嵌套的序列化案例类Duckling Entity？

Answer 1

json4s将递归地解析嵌套对象，因此您不需要自定义序列化程序。

问题是你应该在你的反序列化类中放入JSON类型（JValue和JField），你应该只放置适当的case类。以下是应该在没有任何自定义序列化程序的情况下解析的类的修改版本：

case class DucklingValue(
  value: Int,
  typ: String
)

case class DucklingEntity(
  body: String,
  start: Int,
  end: Int,
  value: DucklingValue,
  dim: String,
  latent: Boolean
)

case class DucklingList(
  list: List[DucklingEntity]
)

---

另请注意，反序列化器具有限制性，因为它们要求字段按您指定的特定顺序排列。最好提取单个字段，如下所示：

case obj: JObject =>
  DucklingValue(
    (obj \ "value").Extract[Int],
    (obj \ "type").Extract[String]
  )

这也允许字段按任何顺序排列。使用这种方法还允许您处理可选字段等，简单的match表达式不能。