如何通过字符串名称及其原始类型来获取字段值的Reflection

Question

尝试通过其字符串名称获取对象字段时,返回的值不是正确的scala类型.如:

import scala.language.reflectiveCalls
import scala.language.implicitConversions

case class Intity(flag: Boolean, id: Int, name: String)
val inty =  Intity(false, 123, "blue")

implicit def reflect(r: AnyRef) = new {
  def get(n:String) = {
    val c = r.getClass.getDeclaredField(n)
    c.setAccessible(true); c}
  def getVal(n: String) = get(n).get(r)
  def getType (n:String) = get(n).getType
 }

然后使用这个

inty.getType("flag")     // res0: Class[_] = boolean  --not Boolean
inty.getVal("id")        // res1: Object = 123    --Object not Int

任何有效的方法来执行上述实现？

Answer 1

不确定,如何从单个函数返回不同类型.但是你可以使用scala反映api来推断任何Class属性的正确类型.

import scala.reflect.runtime.{universe => ru}
implicit class ForAnyInstance[T: ru.TypeTag](i: T)(implicit c: scala.reflect.ClassTag[T]) {

    /* a mirror sets a scope of the entities on which we have reflective access */
    val mirror = ru.runtimeMirror(getClass.getClassLoader)

    /* here we get an instance mirror to reflect on an instance */
    val im = ru.runtimeMirror(i.getClass.getClassLoader)

    def fieldInfo(name: String) = {
      ru.typeOf[T].members.filter(!_.isMethod).filter(_.name.decoded.trim.equals(name)).foreach(s => {
        val fieldValue = im.reflect(i).reflectField(s.asTerm).get

        /* typeSignature contains runtime type information about a Symbol */
        s.typeSignature match {
          case x if x =:= ru.typeOf[String] => /* do something */
          case x if x =:= ru.typeOf[Int] => /* do something */
          case x if x =:= ru.typeOf[Boolean] => /* do something */
        }
      })
    }
}

然后将其调用为:

case class Entity(flag: Boolean, id: Int, name: String)
val e = Entity(false, 123, "blue")
e.fieldInfo("flag")
e.fieldInfo("id")

Answer 2

您可以在编译时使用 shapeless 执行类似的操作。

scala> import shapeless._
import shapeless._

scala> val inty = Intity(false, 123, "blue")
inty: Intity = Intity(false,123,blue)        

scala> val intyGen = LabelledGeneric[Intity].to(inty)
intyGen: shapeless.::[Boolean with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("flag")],Boolean],shapeless.::[Int with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("id")],Int],shapeless.::[String with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("name")],String],shapeless.HNil]]] = false :: 123 :: blue :: HNil

scala> import shapeless.record._
import shapeless.record._

scala> intyGen.get('flag)
res10: Boolean = false

scala> intyGen.get(Symbol("id"))
res11: Int = 123