JSON4S 类型提示不起作用

Question

以下测试片段

implicit val formats = DefaultFormats + FullTypeHints(Contacts.classList)

val serialized = Serialization.write(List(Mail(field = "random@mail.com", note = "Random note.")))
println(serialized)

Serialization.read[List[Contact[_]]](serialized).isInstanceOf[List[Mail]] should be (true)

失败

Can't find constructor for Contact[Object]
org.json4s.package$MappingException: Can't find constructor for Contact[Object]
    at org.json4s.reflect.package$.fail(package.scala:95)
    at org.json4s.reflect.ScalaSigReader$$anonfun$5.apply(ScalaSigReader.scala:21)
    at org.json4s.reflect.ScalaSigReader$$anonfun$5.apply(ScalaSigReader.scala:21)
    at scala.Option.getOrElse(Option.scala:121)
    at org.json4s.reflect.ScalaSigReader$.readConstructor(ScalaSigReader.scala:21)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder.ctorParamType(Reflector.scala:93)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder$$anonfun$createConstructorDescriptors$3$$anonfun$15.apply(Reflector.scala:156)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder$$anonfun$createConstructorDescriptors$3$$anonfun$15.apply(Reflector.scala:142)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
    at scala.collection.AbstractTraversable.map(Traversable.scala:104)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder$$anonfun$createConstructorDescriptors$3.apply(Reflector.scala:142)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder$$anonfun$createConstructorDescriptors$3.apply(Reflector.scala:136)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
    at scala.collection.mutable.ArraySeq.foreach(ArraySeq.scala:74)
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
    at scala.collection.AbstractTraversable.map(Traversable.scala:104)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder.createConstructorDescriptors(Reflector.scala:136)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder.constructorsAndCompanion(Reflector.scala:121)
    at org.json4s.reflect.Reflector$ClassDescriptorBuilder.result(Reflector.scala:183)
    at org.json4s.reflect.Reflector$.createDescriptor(Reflector.scala:53)
    at org.json4s.reflect.Reflector$$anonfun$describe$1.apply(Reflector.scala:48)
    at org.json4s.reflect.Reflector$$anonfun$describe$1.apply(Reflector.scala:48)
    at org.json4s.reflect.package$Memo.apply(package.scala:36)
    at org.json4s.reflect.Reflector$.describe(Reflector.scala:48)
    at org.json4s.Extraction$$anonfun$extract$6.apply(Extraction.scala:393)
    at org.json4s.Extraction$$anonfun$extract$6.apply(Extraction.scala:392)
    at org.json4s.Extraction$.customOrElse(Extraction.scala:606)
    at org.json4s.Extraction$.extract(Extraction.scala:392)
    at org.json4s.Extraction$CollectionBuilder$$anonfun$7.apply(Extraction.scala:410)
    at org.json4s.Extraction$CollectionBuilder$$anonfun$7.apply(Extraction.scala:410)
    at scala.collection.immutable.List.map(List.scala:284)
    at org.json4s.Extraction$CollectionBuilder.mkCollection(Extraction.scala:410)
    at org.json4s.Extraction$CollectionBuilder.result(Extraction.scala:430)
    at org.json4s.Extraction$$anonfun$extract$5.apply(Extraction.scala:382)
    at org.json4s.Extraction$$anonfun$extract$5.apply(Extraction.scala:382)
    at org.json4s.Extraction$.customOrElse(Extraction.scala:606)
    at org.json4s.Extraction$.extract(Extraction.scala:382)
    at org.json4s.Extraction$.extract(Extraction.scala:39)
    at org.json4s.ExtractableJsonAstNode.extract(ExtractableJsonAstNode.scala:21)
    at org.json4s.jackson.Serialization$.read(Serialization.scala:50)
    at org.json4s.Serialization$class.read(Serialization.scala:30)
    at org.json4s.jackson.Serialization$.read(Serialization.scala:17)

哪里Contact是

abstract class Contact[Field : Validable](
  val field: Field,
  val created: Long,
  val updated: Long,
  val note: String) { }

和 Mail是

case class Mail(
  override val field: String,
  override val created: Long = System.currentTimeMillis(),
  override val updated: Long = System.currentTimeMillis(),
  override val note: String)
extends Contact[String](field, created, updated, note)(Mail)

case object Mail extends Validable[String] {
  override def valid(field: String): Boolean = {
    Validator.email(field)
  }
}

和测试输出是

[{"jsonClass":"whatever.core.entities.utility.contact.Mail","field":"random@mail.com","created":1508428385266,"updated":1508428385266,"note":"Random note."}]

深入研究 JSON4S 的代码库表明根本没有使用类型提示。

如何强制 JSON4S 使用类型提示？

干杯

Answer 1

实现 Contact使用 trait s，它会起作用。