斯卡拉地图案例类转换

Question

我想Scala的地图[字符串，任何]转换为使用Scala的反射（斯卡拉2.11）的情况下，类如下 -

val m = Map("name" -> "ABC", "age" -> 7, "gender" -> "male") 
case class someCC(name: String, age: Int, gender: String) 

import scala.reflect.ClassTag 

    def createCaseClass[T](someMap : Map[String, Any])(implicit someClassTag : ClassTag[T]) = { 

    val ctor = someClassTag.runtimeClass.getConstructors.head 
    val args = someClassTag.runtimeClass.getDeclaredFields.map(x => someMap(x.getName)) 

     ctor.newInstance(args: _*).asInstanceOf[T] 
    } 

这个不幸导致编译错误 -

Name: Unknown Error 
Message: <console>:106: error: type mismatch; 
found : Array[Any] 
required: Array[_ <: Object] 
Note: Any >: Object, but class Array is invariant in type T. 
You may wish to investigate a wildcard type such as `_ >: Object`. (SLS 3.2.10) 
       ctor.newInstance(args: _*).asInstanceOf[T] 
         ^

我是相当新的使用ClassTags，我明白，这个错误主要是因为java.lang.Object继承是任何一个子集，任何可能包括非Java对象。

当我尝试将Any替换为AnyRef（它对应于JRE中的java.lang.Object）时，该函数调用会导致类型不匹配错误。

import scala.reflect.ClassTag 

    def createCaseClass[T](someMap : Map[String, AnyRef])(implicit someClassTag : ClassTag[T]) = { 

    val ctor = someClassTag.runtimeClass.getConstructors.head 
    val args = someClassTag.runtimeClass.getDeclaredFields.map(x => someMap(x.getName)) 

     ctor.newInstance(args: _*).asInstanceOf[T] 
    } 

val someCC = createCaseClass[someCC](m) 

Name: Unknown Error 
Message: <console>:106: error: type mismatch; 
found : scala.collection.immutable.Map[String,Any] 
required: Map[String,AnyRef] 
     val someCC = createCaseClass[someCC](m) 

解决此错误的最佳方法是什么？建议感激。谢谢！

更新1 - 更新此隐式地将Any转换为AnyRef导致函数调用时出现错误“java.util.NoSuchElementException”。

import scala.reflect.ClassTag 
import scala.reflect.runtime.universe._ 

    def createMyClass[T](someMap : Map[String, Any])(implicit someClassTag : ClassTag[T]) = { 

     val ctor = someClassTag.runtimeClass.getConstructors.head 

     val args = someClassTag.runtimeClass.getDeclaredFields.map(x => someMap(x.getName)) 

     ctor.newInstance(args.asInstanceOf[Seq[AnyRef]]: _*).asInstanceOf[T] 

} 

val m = Map("name" -> "ABC", "age" -> 7, "gender" -> "male") 
case class someCC(name: String, age: Int, gender: String) 

createMyClass[someCC](m) 

Name: java.util.NoSuchElementException 
Message: key not found: $outer 
StackTrace: at scala.collection.MapLike$class.default(MapLike.scala:228) 
    at scala.collection.AbstractMap.default(Map.scala:59) 
    at scala.collection.MapLike$class.apply(MapLike.scala:141) 
    at scala.collection.AbstractMap.apply(Map.scala:59) 
    at $$$e75186ae1b35495ffea8e318378149a$$$$anonfun$1.apply(<console>:135) 
    at $$$e75186ae1b35495ffea8e318378149a$$$$anonfun$1.apply(<console>:135) 
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) 
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) 
    at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33) 
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186) 
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:234) 
    at scala.collection.mutable.ArrayOps$ofRef.map(ArrayOps.scala:186) 
    at createMyClass(<console>:135) 

我在这里做错了什么？

Answer 1

使用强制：

ctor.newInstance(args.asInstanceOf[Seq[AnyRef]]: _*).asInstanceOf[T] 

请注意，您映射的情况下类的每个场构造PARAM。这是不正确的，因为case类可能有不在构造函数中的字段，并且您的代码会中断。

更好的方法是使用Scala的反思：

import reflect.runtime.universe._ 

def mkClassInstance[T: TypeTag](args: Map[String, Any]): T = { 
    val rMirror = runtimeMirror(getClass.getClassLoader) 
    val cMirror = rMirror.reflectClass(typeOf[T].typeSymbol.asClass) 
    // The primary constructor is the first one 
    val ctor = typeOf[T].decl(termNames.CONSTRUCTOR).asTerm.alternatives.head.asMethod 
    val argList = ctor.paramLists.flatten.map(param => args(param.name.toString)) 
    cMirror.reflectConstructor(ctor)(argList: _*).asInstanceOf[T] 
} 
def mkInnerClassInstance[T: TypeTag](outer: Any)(args: Map[String, Any]): T = { 
    val rMirror = runtimeMirror(getClass.getClassLoader) 
    val cMirror = rMirror.reflect(outer).reflectClass(typeOf[T].typeSymbol.asClass) 
    // The primary constructor is the first one 
    val ctor = typeOf[T].decl(termNames.CONSTRUCTOR).asTerm.alternatives.head.asMethod 
    val argList = ctor.paramLists.flatten.map(param => args(param.name.toString)) 
    cMirror.reflectConstructor(ctor)(argList: _*).asInstanceOf[T] 
}