问题描述
我得到了像 {"name":"susan","age":25} 这样的 json，以及像 "name:String,age:Int" 这样的 json 键集的提示，如何从那个json?
I got json like {"name":"susan","age":25},and a hint to json keyset like "name:String,age:Int",how to create a HList from that json?
推荐答案
基于您添加然后删除的代码，似乎有一个运行时字符串提示 "name:String,age:Int" 和运行时字符串 json {"name":"susan","age";:25}，你想得到一个 HList 和 运行时反射.您可以按以下方式执行此操作
Based on the code you added and then deleted, it seems, having a runtime-string hint "name:String,age:Int" and runtime-string json {"name":"susan","age":25}, you want to get an HList with runtime reflection. You can do this as follows
import shapeless.HList
import scala.reflect.runtime
import scala.reflect.runtime.universe._
import scala.tools.reflect.ToolBox
val tb = runtime.currentMirror.mkToolBox()
val jsonStr = """{"name":"susan","age":25}"""
val hint = "name:String,age:Int"
val classType = tb.define(tb.parse(s"case class Test($hint)").asInstanceOf[ImplDef]).asClass.toType
val hlist = tb.eval(q"""
import io.circe.generic.auto._
import io.circe.parser.decode
val classInstance = decode[$classType]($jsonStr)
import shapeless.Generic
Generic[$classType].to(classInstance.toOption.get)
""").asInstanceOf[HList]
println(hlist) // susan :: 25 :: HNil
请注意，您在运行时执行所有操作，因此您将无法在编译时访问 String :: Int :: HNil 类型，而 hlist 仅具有静态类型HList (not String :: Int :: HNil) 和 HList 实际上并不比 List[Any] 好>.
Please notice that you do everything at runtime so you'll have no access to type String :: Int :: HNil at compile time and hlist has static type just HList (not String :: Int :: HNil) and HList is actually not better than just List[Any].
build.sbt
libraryDependencies ++= Seq(
scalaOrganization.value % "scala-reflect" % scalaVersion.value,
scalaOrganization.value % "scala-compiler" % scalaVersion.value,
"com.chuusai" %% "shapeless" % "2.4.0-M1",
"io.circe" %% "circe-core" % "0.13.0",
"io.circe" %% "circe-parser" % "0.13.0",
"io.circe" %% "circe-generic" % "0.13.0"
)
实际上，我想我们做了一些奇怪的事情.我们使用高度类型级别的库(shapeless、circe) 旨在实现静态类型安全，然后在运行时通过反射运行它们，忽略类型安全并实际获取 List[Any] (HList).
Actually, I guess we do someting strange. We use highly type-level libraries (shapeless, circe) aimed to static type safety and then run them at runtime with reflection ignoring type safety and getting actually List[Any] (HList).
我想如果 List[Any](字段值列表)对你来说足够了，那么你只需要使用更多的运行时库.例如，使用 json4s
I guess that if List[Any] (list of field values) is enough for you then you just need to use a more runtime library. For example, with json4s
import org.json4s.{JInt, JObject, JString, JValue}
import org.json4s.jackson.JsonMethods._
val jsonStr: String = """{"name":"susan","age":25}"""
val json: JValue = parse(jsonStr) //JObject(List((name,JString(susan)), (age,JInt(25))))
val l: List[JValue] = json.asInstanceOf[JObject].obj.map(_._2) //List(JString(susan), JInt(25))
val res: List[Any] = l.map {
case JString(s) => s
case JInt(n) => n
} //List(susan, 25)
build.sbt
libraryDependencies += "org.json4s" %% "json4s-jackson" % "3.6.9"
其实用Circe也可以做到，只是用parse代替decode[A]
import io.circe.{Json, JsonNumber}
import io.circe.parser.parse
val jsonStr: String = """{"name":"susan","age":25}"""
val json: Json = parse(jsonStr).toOption.get //{"name":"susan","age":25}
val l: List[Json] = json.asObject.get.values.toList //List("susan", 25)
val res: List[Any] = l.map(_.fold[Any](null, null, (_: JsonNumber).toInt.get, identity[String], null, null)) //List(susan, 25)
如果你需要一个 case 类的实例或者一个元组而不是 HList 替换
tb.eval(q"""
import io.circe.generic.auto._
import io.circe.parser.decode
val classInstance = decode[$classType]($jsonStr)
import shapeless.Generic
Generic[$classType].to(classInstance.toOption.get)
""").asInstanceOf[HList] // susan :: 25 :: HNil
与
tb.eval(q"""
import io.circe.generic.auto._
import io.circe.parser.decode
decode[$classType]($json).toOption.get
""").asInstanceOf[Product] //Test(susan,25)
或
tb.eval(q"""
import io.circe.generic.auto._
import io.circe.parser.decode
val classInstance = decode[$classType]($json)
import shapeless.Generic
Generic[$classType].to(classInstance.toOption.get).tupled
""").asInstanceOf[Product] //(susan,25)
相应地.
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