如何解决在任意Scala对象中调用私有方法
object SomeObject {
private def someMethod(msg: String): Unit = println(msg)
}
我可以使用以下代码调用someMethod
:
import scala.reflect.runtime.{universe => ru}
import scala.reflect.classtag
def invokeObjectPrivateMethod[R](methodName: String,args: AnyRef*): R = {
val rm = ru.runtimeMirror(getClass.getClassLoader)
val instanceMirror = rm.reflect(SomeObject)
val methodSymbol = ru.typeOf[SomeObject.type].decl(ru.TermName(methodName)).asMethod
val method = instanceMirror.reflectMethod(methodSymbol)
method(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod("someMethod","it works")
但是在上面,我已经将SomeObject
硬编码到函数中。我真正想要的是传递一个任意的对象名称/类标记/任何内容,这样我就可以在ANY对象中通用地调用私有函数。
这些尝试无效:
// With explicit classtag parameter
def invokeObjectPrivateMethod2[R](classtag: classtag[_],methodName: String,args: AnyRef*): R = {
val rm = ru.runtimeMirror(getClass.getClassLoader)
val instanceMirror = rm.reflect(classtag)
val methodSymbol = ru.typeOf[classtag.type].decl(ru.TermName(methodName)).asMethod
val method = instanceMirror.reflectMethod(methodSymbol)
method(args: _*).asInstanceOf[R]
}
// This fails at runtime with: `scala.ScalaReflectionException: <none> is not a method`
invokeObjectPrivateMethod2[Unit](classtag(SomeObject.getClass),"someMethod","it doesn't work")
// With implicit classtag/TypeTag
def invokeObjectPrivateMethod3[T: classtag,S: ru.TypeTag,R](methodName: String,args: AnyRef*)(implicit ct: classtag[T]): R = {
val rm = ru.runtimeMirror(getClass.getClassLoader)
val instanceMirror = rm.reflect(ct)
val methodSymbol = ru.typeOf[S].decl(ru.TermName(methodName)).asMethod
val method = instanceMirror.reflectMethod(methodSymbol)
method(args: _*).asInstanceOf[R]
}
// This fails at compile time: `not found: type SomeObject`
invokeObjectPrivateMethod3[SomeObject,SomeObject,Unit]("someMethod","it also doesn't work")
我有点不了解,所以我尝试使用第三个选项可能甚至没有意义。
谢谢!
解决方法
如果对象名称为String
,请尝试以下操作
def invokeObjectPrivateMethod[R](objectName: String,methodName: String,args: AnyRef*): R = {
val rm = scala.reflect.runtime.currentMirror
val moduleSymbol = rm.staticModule(objectName)
val classSymbol = moduleSymbol.moduleClass.asClass
val moduleMirror = rm.reflectModule(moduleSymbol)
val objectInstance = moduleMirror.instance
val objectType = classSymbol.toType
val methodSymbol = objectType.decl(ru.TermName(methodName)).asMethod
val instanceMirror = rm.reflect(objectInstance)
val methodMirror = instanceMirror.reflectMethod(methodSymbol)
methodMirror(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod("com.example.App.SomeObject","someMethod","it works") //it works
或者如果您有对象ClassTag
def invokeObjectPrivateMethod[R](classTag: ClassTag[_],args: AnyRef*): R = {
val rm = scala.reflect.runtime.currentMirror
val clazz = classTag.runtimeClass
val classSymbol = rm.classSymbol(clazz)
val moduleSymbol = classSymbol.owner.info.decl(classSymbol.name.toTermName).asModule //see (*)
val moduleMirror = rm.reflectModule(moduleSymbol)
val objectInstance = moduleMirror.instance
val objectType = classSymbol.toType
val methodSymbol = objectType.decl(ru.TermName(methodName)).asMethod
val instanceMirror = rm.reflect(objectInstance)
val methodMirror = instanceMirror.reflectMethod(methodSymbol)
methodMirror(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod(classTag[SomeObject.type],"it works") //it works
或者如果您有对象TypeTag
def invokeObjectPrivateMethod[R](typeTag: TypeTag[_],args: AnyRef*): R = {
val rm = scala.reflect.runtime.currentMirror
val objectType = typeTag.tpe
val clazz = rm.runtimeClass(objectType) // see (**)
val classSymbol = rm.classSymbol(clazz)
val moduleSymbol = classSymbol.owner.info.decl(classSymbol.name.toTermName).asModule // see (*)
val moduleMirror = rm.reflectModule(moduleSymbol)
val objectInstance = moduleMirror.instance
val methodSymbol = objectType.decl(ru.TermName(methodName)).asMethod
val instanceMirror = rm.reflect(objectInstance)
val methodMirror = instanceMirror.reflectMethod(methodSymbol)
methodMirror(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod(typeTag[SomeObject.type],"it works") //it works
或者如果您有对象Class
def invokeObjectPrivateMethod[R](clazz: Class[_],args: AnyRef*): R = {
val rm = scala.reflect.runtime.currentMirror
val classSymbol = rm.classSymbol(clazz)
val moduleSymbol = classSymbol.owner.info.decl(classSymbol.name.toTermName).asModule //see (*)
val moduleMirror = rm.reflectModule(moduleSymbol)
val objectInstance = moduleMirror.instance
val objectType = classSymbol.toType
val methodSymbol = objectType.decl(ru.TermName(methodName)).asMethod
val instanceMirror = rm.reflect(objectInstance)
val methodMirror = instanceMirror.reflectMethod(methodSymbol)
methodMirror(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod(SomeObject.getClass,"it works") //it works
或者如果您有对象Type
def invokeObjectPrivateMethod[R](typ: Type,args: AnyRef*): R = {
val rm = scala.reflect.runtime.currentMirror
val classSymbol = typ.typeSymbol.asClass
val moduleSymbol = classSymbol.owner.info.decl(classSymbol.name.toTermName).asModule //see (*)
val moduleMirror = rm.reflectModule(moduleSymbol)
val objectInstance = moduleMirror.instance
val methodSymbol = typ.decl(ru.TermName(methodName)).asMethod
val instanceMirror = rm.reflect(objectInstance)
val methodMirror = instanceMirror.reflectMethod(methodSymbol)
methodMirror(args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod(typeOf[SomeObject.type],"it works") //it works
(*)Get the module symbol,given I have the module class,scala macro
(**)How to get ClassTag form TypeTag,or both at same time?
我认为该方法没有重载版本,否则您应该使用typ.decl(...).alternatives.find(...).get.asMethod
或typ.decl(...).alternatives.head.asMethod
。
使用Java反射
def invokeObjectPrivateMethod[R](packageName: String,objectName: String,args: AnyRef*): R = {
val javaClassName = s"$packageName.${objectName.replace('.','$')}$$"
val clazz = Class.forName(javaClassName)
val method = clazz.getDeclaredMethods.find(_.getName == methodName).get
method.setAccessible(true)
val field = clazz.getField("MODULE$")
val instance = field.get(null) // null because field is static
method.invoke(instance,args: _*).asInstanceOf[R]
}
invokeObjectPrivateMethod("com.example","App.SomeObject","it works") //it works
使用Java方法句柄
def invokeObjectPrivateMethod[R](packageName: String,'$')}$$"
val clazz = Class.forName(javaClassName)
val lookup = MethodHandles.lookup
val field = clazz.getField("MODULE$")
val fieldMethodHandle = lookup.unreflectGetter(field)
val instance = fieldMethodHandle.invokeWithArguments()
val method = clazz.getDeclaredMethods.find(_.getName == methodName).get
method.setAccessible(true)
val methodHandle = lookup.unreflect(method)
methodHandle.invokeWithArguments(instance +: args : _*).asInstanceOf[R]
}
invokeObjectPrivateMethod("com.example","it works") //it works
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