scala 将字符串转换为泛型类型 [英] scala convert String to generic type

问题描述

我正在解析一个 json.我想将它的值转换为其他类型.即

I am am parsing a json. I would like to convert it's values to other types . i.e

//json = JSON String 
val seq = net.liftweb.json.parse(json).\\("seq").values.toString.toLong
val userName = net.liftweb.json.parse(json).\\("name").values.toString
val intNum = net.liftweb.json.parse(json).\\("intId").values.toInt

我想使用泛型方法更scala"的方式来转换它，我尝试了这样的事情:

I would like to cast it using generic method more "scala" way, I tried something like this:

object Converter{
  def JSONCaster[T](json:String,s:String):T={
    net.liftweb.json.parse(json).\\(s).values.toString.asInstanceOf[T]
  }
}

但是遇到了铸造错误:

java.lang.ClassCastException: java.lang.String 不能转换为java.lang.Long at scala.runtime.BoxesRunTime.unboxToLong(Unknown来源)

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long at scala.runtime.BoxesRunTime.unboxToLong(Unknown Source)

推荐答案

我遇到了同样的问题，我记得 Play 框架有一些功能可以做类似的事情.在挖掘源代码后，我发现了这个 课程.

I had the same problem and remembered that Play framework had some functionality that did something similar. After digging through the source I found this Class.

基本上，我们可以这样做:

Basically, we can do something like this:

object JSONCaster {

  def fromJson[T](json: String, s: String)(implicit converter: Converter[T]): T = {
    converter.convert(net.liftweb.json.parse(json).\\(s).values.toString)
  }

  trait Converter[T] { self =>
    def convert(v: String): T
  }

  object Converter{
    implicit val longLoader: Converter[Long] = new Converter[Long] {
      def convert(v: String): Long = v.toLong
    }

    implicit val stringLoader: Converter[String] = new Converter[String] {
      def convert(v: String): String = v
    }

    implicit val intLoader: Converter[Int] = new Converter[Int] {
      def convert(v: String): Long = v.toInt
    }

    // Add any other types you want to convert to, even custom types!
  }
}

可以这样称呼:

JSONCaster.fromJson[Long](json, "seq")

缺点是我们必须为我们想要转换的所有类型定义隐式转换器.这样做的好处是使界面非常干净且可重用.

The downside is we have to define implicit converters for all the types we want to cast to. The upside being this keeps the interface really clean and reusable.

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