使用Json4s时，如何从json中删除空/无效字段？

Question

如果我有以下内容：

object Json4sTest extends App {
  val info = new TestObject("Johnny", "USA")
  println(info)
}

case class TestObject(
  name: String,
  companyName: String,
  var countryCode: Option[String] = None,
  var countryName: Option[String] = None,
  var zip: Option[Int] = None
) {

  override def toString: String = {
    compact(render(
      ("name" -> name) ~
      ("companyName" -> countryCode) ~
      ("countryCode" -> (if (countryCode.isDefined) countryCode.get else StringUtils.EMPTY)) ~
      ("countryName" -> (if (countryName.isDefined) countryName.get else StringUtils.EMPTY)) ~
      ("zip" -> (if (zip.isDefined) zip.get else -1))
    ))
  }
}

那将输出类似：

{"name":"Johnny","companyName":"Some Company","countryCode":"","countryName":"","zip":-1}

我想要的预期输出是：

{"name":"Johnny","companyName":"Some Company"}

我该怎么做？

这行得通，但是想像一下，如果我有一个带有15个字段的值对象，那么字符串就会变得很大。

Answer 1

根据您的预期响应，您可以使用Json4s的内置方法write 。

  override def toString: String = {
      implicit val formats = DefaultFormats
      write(this)
    }
 val info = new TestObject("Johnny", "USA")

//> info  : TestObject = {"name":"Johnny","companyName":"USA"}
 

您需要的进口是

import org.json4s.native.Serialization.write                                          

Answer 2

事实证明，Json4s足够聪明，可以忽略“无”字段

所以最终结果超过了

override def toString: String = {
   compact(render(
    ("name" -> name) ~
    ("companyName" -> companyName) ~
    ("countryCode" -> countryCode) ~
    ("countryName" -> countryName) ~
    ("zip" -> zip)
  ))
}