访问Companion对象中的专用字段
我有一个类陪同对象的TestClass 。 如何在scala中使用运行时反射来访问私有字段，例如在类中设置私有字段时，在配对对象中声明xyz ，如下所示。
class TestClass { TestClass.xyz = 100 }
object TestClass { private var xyz: Int = _ }
我尝试了以下
import scala.reflect.runtime.{currentMirror, universe => ru}
val testModuleSymbol = ru.typeOf[TestClass.type].termSymbol.asModule
val moduleMirror = currentMirror.reflectModule(testModuleSymbol)
val instanceMirror = currentMirror.reflect(moduleMirror.instance)
val xyzTerm = ru.typeOf[TestClass.type].decl(ru.TermName("xyz")).asTerm.accessed.asTerm
val fieldMirror = instanceMirror.reflectField(xyzTerm)
val context = fieldMirror.get.asInstanceOf[Int]
但我得到了下面的错误。
scala> val fieldMirror = instanceMirror.reflectField(xyzTerm)
scala.ScalaReflectionException: Scala field xyz of object TestClass isn't represented as a Java field, nor does it have a
Java accessor method. One common reason for this is that it may be a private class parameter
not used outside the primary constructor.
at scala.reflect.runtime.JavaMirrors$JavaMirror.scala$reflect$runtime$JavaMirrors$JavaMirror$$abort(JavaMirrors.scala:115)
at scala.reflect.runtime.JavaMirrors$JavaMirror.scala$reflect$runtime$JavaMirrors$JavaMirror$$ErrorNonExistentField(JavaMirrors.scala:127)
at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaInstanceMirror.reflectField(JavaMirrors.scala:242)
at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaInstanceMirror.reflectField(JavaMirrors.scala:233)
... 29 elided
只有当我引用TestClass中的变量xyz （即TestClass.xyz = 100 ）时才引发此异常。 如果这个引用从类中删除，那么我的示例代码就可以正常工作。
得到这个工作：
import scala.reflect.runtime.universe._
import scala.reflect.runtime.{universe => ru}
val runMirror = ru.runtimeMirror(getClass.getClassLoader)
val objectDef = Class.forName("org.myorg.TestClass")
val objectTypeModule = runMirror.moduleSymbol(objectDef).asModule
val objectType = objectTypeModule.typeSignature
val methodMap = objectType.members
.filter(_.isMethod)
.map(d => {
d.name.toString -> d.asMethod
})
.toMap
// get the scala Object
val instance = runMirror.reflectModule(objectTypeModule).instance
val instanceMirror = runMirror.reflect(instance)
// get the private value
val result = instanceMirror.reflectMethod(methodMap("xyz")).apply()
assert(result == 100)