多个不同类型对象如何统一JSon序列化小技巧

object JsonUtils {
  /** Used to convert between classes and JSON. */
  val mapper = new ObjectMapper with ScalaObjectMapper
  mapper.setSerializationInclusion(Include.NON_ABSENT)
  mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
  mapper.registerModule(DefaultScalaModule)

  def toJson[T: Manifest](obj: T): String = {
    mapper.writeValueAsString(obj)
  }

  def toPrettyJson[T: Manifest](obj: T): String = {
    mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj)
  }

  def fromJson[T: Manifest](json: String): T = {
    mapper.readValue[T](json)
  }
}

sealed trait Action {
  def wrap: SingleAction
  def json: String = JsonUtils.toJson(wrap)
}

override def wrap: SingleAction = SingleAction(add = this)

/** A serialization helper to create a common action envelope. */
case class SingleAction(
    txn: SetTransaction = null,
    add: AddFile = null,
    remove: RemoveFile = null,
    metaData: Metadata = null,
    protocol: Protocol = null,
    commitInfo: CommitInfo = null) {

  def unwrap: Action = {
    if (add != null) {
      add
    } else if (remove != null) {
      remove
    } else if (metaData != null) {
      metaData
    } else if (txn != null) {
      txn
    } else if (protocol != null) {
      protocol
    } else if (commitInfo != null) {
      commitInfo
    } else {
      null
    }
  }
}