使用json4s序列化时删除json字段（当为空值时）

Question

使用json4s序列化删除json字段（空值时）的最佳做法是什么？

val json = ("foo" -> "bar") ~ ("fizz" -> "buzz")
compact(render(json))
""" {"foo":"bar","fizz":"buzz"} """


val json = ("foo" -> "bar") ~ ("fizz" -> "")
compact(render(json))
""" {"foo":"bar"} """

Answer 1

1. 使用EmptyValueStrategy（如果序列化JValue）

val formats = DefaultFormats.withEmptyValueStrategy(new EmptyValueStrategy {

  def noneValReplacement = None

  def replaceEmpty(value: JValue): JValue = {
    case JString("") => JNothing
    case JArray(items) => JArray(items map replaceEmpty)
    case JObject(fields) => JObject(fields map {
      case JField(name, v) => JField(name, replaceEmpty(v))
    })
    case oth => oth
  }
})
compact(render(("foo" -> "bar") ~ ("fizz" -> "")))

1. 使用CustomSerializer（如果序列化案例类）

val customSerializer = new CustomSerializer[String](_ => ({ case JString(s) => s }, { case "" => JNothing case s: String => JString(s) }))
implicit val jsonFormat = DefaultFormats + customSeirializer

case class Foo(a: Int, b: String)
Serialization.write(Foo(42, ""))