Json4s在序列化期间忽略None字段（而不是使用'null'）

我假设您想将

None

null

DefaultFormats.preservingEmptyValues

import java.util.Dateimport org.json4s._import org.json4s.jackson.Serializationobject test extends App {  implicit val f = DefaultFormats.preservingEmptyValues // requires version>=3.2.11  case class JsonTest(x: String, y: Option[String], z: Option[Int], a: Option[Double], b: Option[Boolean], c:Option[Date], d: Option[Any])  val v = JsonTest("test", None, None, None, None, None, None);  // prints {"x":"test","y":null,"z":null,"a":null,"b":null,"c":null,"d":null}  println(Serialization.write(v))}