json4s：无法用重命名的字段解析 JSON

Question

我需要序列化然后反序列化 case class 对象，其字段 "name" 来自 JSON，它具有 "animalname" 字段而不是 "name"。序列化工作正常，但反序列化不行。我将 FieldSerializer 与 renameTo() 和 renameFrom():

一起使用

import org.json4s._
import org.json4s.FieldSerializer._
import org.json4s.jackson.Serialization._

case class WildDog(name: String)
val dogSerializer = FieldSerializer[WildDog](
  renameTo("name", "animalname"),
  renameFrom("animalname", "name"))
implicit val formats = DefaultFormats + dogSerializer
// serialize
val json = write(WildDog("beefy")) // {"animalname":"beefy"}, as expected
// try to deserialize
val dog = parse(json).extract[WildDog] // expected: Dog("beefy")

实际上，extract() 抛出异常：

org.json4s.package$MappingException: No usable value for name
Did not find value which can be converted into java.lang.String
    at org.json4s.reflect.package$.fail(ws.sc:94)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$buildCtorArg(ws.sc:409)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun.apply(ws.sc:417)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun.apply(ws.sc:417)
    at scala.collection.TraversableLike$$anonfun$map.apply(ws.sc:240)
    at scala.collection.TraversableLike$$anonfun$map.apply(ws.sc:240)
    at scala.collection.mutable.ResizableArray$class.foreach(ws.sc:55)
    at scala.collection.mutable.ArrayBuffer.foreach(ws.sc:43)
    at scala.collection.TraversableLike$class.map(ws.sc:240)
    at scala.collection.AbstractTraversable.map(ws.sc:101)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$instantiate(ws.sc:417)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result.apply(ws.sc:445)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result.apply(ws.sc:442)
    at org.json4s.Extraction$.org$json4s$Extraction$$customOrElse(ws.sc:454)
    at org.json4s.Extraction$ClassInstanceBuilder.result(ws.sc:442)
    at org.json4s.Extraction$.extract(ws.sc:304)
    at org.json4s.Extraction$.extract(ws.sc:38)
    at org.json4s.ExtractableJsonAstNode.extract(ws.sc:17)

如何正确反序列化此 JSON？

更新：我使用 Scala 2.10，json4s 3.2.5。

更新 2：我将此 Maven 依赖项用于 json4s：

<dependency>
    <groupId>org.json4s</groupId>
    <artifactId>json4s-jackson_2.10</artifactId>
    <version>3.2.5</version>
</dependency>

Answer 1

尝试 val dog = read[WildDog](json) 而不是 val dog = parse(json).extract[WildDog]

github 页面 - https://github.com/json4s/json4s 还有其他一些很好的示例。

编辑：

Working versions:
Scala 2.10 && org.json4s.jackson >= 3.5.0
Scala 2.11 && org.json4s.jackson >= 3.2.5

Scala 2.10之前的版本我没有查过，但是我用3.2.5的时候出现异常

另外，我可以让 val dog = parse(json).extract[WildDog] 工作，但你必须导入 JsonMethods -> import org.json4s.jackson.JsonMethods.parse

json4s：无法用重命名的字段解析 JSON

json4s: unable to parse JSON with renamed field

serialization

scala

json4s