Scala 反射生成伴随的 object 并调用 apply 方法

Question

这是问题所在。

trait TestTrait[T, R] extends (T => R) 

// Class implementing TestTrait. This is one class, there are a number of class implementing TestTrait
class TestClass(val input: Map[String, String])extends ConfigurableDomainExtractor[String, String] {
  override def apply(value: String): String = ???
}

// Companion Object
object TestClass {
 def apply(properties: Map[String, String]): TestClass = TestClass(properties)
}

我想做的是在 util class 中定义一个方法让我们说

class CreateInstance {
  def getInstance(fullyQualifiedClassName: String, properties: Map[String, String]): TestTrait = ???

// fullyQualifiedClassName is the name of the class that needs to be instantiated using its companion object. It can be TestClass or any class implementing TestTrait
// properties is the map that needs to be pass to the apply method of the companion object.


}

which will when pass class name, will generate an object of the same class by first getting a companion object and then call apply on the companion object passing the map to generate the class instance.

我知道我们在 scala 中有反射，我尝试了几件事但无济于事。 这是我尝试过的几件事。

  import scala.reflect.runtime.universe

def getInstance(fullyQualifiedClassName: String, properties: Map[String, String]): TestTrait = {
val runtimeMirror = universe.runtimeMirror(getClass.getClassLoader)
    val module        = runtimeMirror.staticModule(fullyQualifiedClassName)
    val obj           = runtimeMirror.reflectModule(module)

      obj.instance
        .asInstanceOf[TestTrait[String, String]]
        .apply(properties)
        .asInstanceOf[TestTrait[String, String]]

}

有人可以帮我完成def getInstance方法。 ?

Answer 1

试试 Scala 反射

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

def getInstance(fullyQualifiedClassName: String, properties: Map[String, String]): TestTrait[String, String] = {
  val runtimeMirror = universe.runtimeMirror(getClass.getClassLoader)
  val objSymbol = runtimeMirror.staticModule(fullyQualifiedClassName)
  val objMirror = runtimeMirror.reflectModule(objSymbol)
  val obj = objMirror.instance
  val objTyp = objSymbol.typeSignature
  val methodSymbol = objTyp.decl(TermName("apply")).asMethod
  val instanceMirror = runtimeMirror.reflect(obj)
  val methodMirror = instanceMirror.reflectMethod(methodSymbol)
  methodMirror(properties).asInstanceOf[TestTrait[String, String]]
}

getInstance("pckg.App.TestClass", Map("a" -> "b"))

或 Java 反射

def getInstance(fullyQualifiedClassName: String, properties: Map[String, String]): TestTrait[String, String] = {
  val clazz = Class.forName(fullyQualifiedClassName)
  val moduleField = clazz.getDeclaredField("MODULE$")
  val obj = moduleField.get(null) // field MODULE$ is static
  val applyMethod = clazz.getDeclaredMethod("apply", classOf[Map[_, _]])
  applyMethod.invoke(obj, properties).asInstanceOf[TestTrait[String, String]]
}

getInstance("pckg.App$TestClass$", Map("a" -> "b"))