从包含Some和None值的列表中使用Json4S生成Json字符串 [英] Generating Json string using Json4S from a list containing Some and None values

问题描述

我正在使用Scalatra，后者又使用Json4S生成Json字符串.我收到

I am using Scalatra, which in turn uses Json4S to generate Json string. I receive

["A"，"B"]

["A","B"]

对于

List(Some("A")，None，Some("B"))

List(Some("A"),None,Some("B"))

我想收到

["A"，未定义，"B"]

["A",undefined,"B"]

如何解决?

推荐答案

undefined即使在javascript中有效，也不是有效的json值. 来自 rfc4627 (应用程序/json):

undefined is not a valid json value, even though it is valid in javascript. From rfc4627 (application/json):

JSON值必须是对象，数组，数字或字符串，或者是以下之一 以下三个文字名称:

A JSON value MUST be an object, array, number, or string, or one of the following three literal names:

false null真

false null true

(未提及未定义)

但是，与null而不是undefined相比，这很简单.在scala控制台中，首先导入几个:

However this is fairly straight-forward to do with null instead of undefined. In the scala console, first a couple imports:

scala> import org.json4s._
scala> import org.json4s.native.Serialization.write

客户序列化程序:

scala> class NoneJNullSerializer extends CustomSerializer[Option[_]](format => ({ case JNull => None }, { case None => JNull }))

瞧，

scala> implicit val formats = DefaultFormats + new NoneJNullSerializer()
scala> val ser = write(List(Some("A"), None, Some("B")))
ser: String = ["A",null,"B"]

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