Question

我正在尝试在Scala中使用json4s解析以下Json，但由于嵌套结构而无法实现：

[
 {
    "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，我只能提取第一个案例类，而不能提取嵌套的类：

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

以下是上面的输出：

[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

我尝试使用json4s提取方法将其与下面列出的案例类和序列化程序一起提取。

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)
  }
))

我如何才能将嵌套的序列化案例类DucklingEntity也提取到DucklingList下？

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器。

问题在于，当您只需要放置适当的case类时，就已经在反序列化类中放置了JSON类型（JValue和JField）。这是您的类的修改后的版本，无需任何自定义序列化程序即可解析：

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]
)

还要注意，反序列化器是限制性的，因为它们要求字段以您指定的特定顺序出现。最好提取单个字段，如下所示：

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

这也允许字段以任何顺序排列。使用这种方法还使您可以处理简单的match表达式无法处理的可选字段等。

在Scala中将带有json4s的嵌套序列化json提取到case类中

1 个答案: