scala - 如何使用 Scala ScriptEngine 调用函数或模块

Question

如何使用 ScriptEngine 调用函数或模块。

这是我的示例代码，编译良好，但在运行时抛出异常 scalaVersion := "2.12.4"and sbt.version = 0.13.16, java is jdk1.8.0_131

import java.io.FileReader
import javax.script._

object DemoApp extends App {
    val engine: ScriptEngine with Compilable with javax.script.Invocable  = new ScriptEngineManager()
    .getEngineByName("scala")
    .asInstanceOf[ScriptEngine with javax.script.Invocable with Compilable]
    val reader = new FileReader("src/main/scala/Demo.sc")
    engine.compile(reader).eval()
    val result = engine.invokeFunction("fun")
}

下面是Demo.sc

def fun: String = {
"Rerutn from Fun"
}

以下是运行时的异常

Exception in thread "main" java.lang.ClassCastException: scala.tools.nsc.interpreter.Scripted cannot be cast to javax.script.Invocable
at DemoApp$.delayedEndpoint$DemoApp$1(DemoApp.scala:13)
at DemoApp$delayedInit$body.apply(DemoApp.scala:5)
at scala.Function0.apply$mcV$sp(Function0.scala:34)
at scala.Function0.apply$mcV$sp$(Function0.scala:34)
at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
at scala.App.$anonfun$main$1$adapted(App.scala:76)
at scala.collection.immutable.List.foreach(List.scala:389)
at scala.App.main(App.scala:76)
at scala.App.main$(App.scala:74)
at DemoApp$.main(DemoApp.scala:5)
at DemoApp.main(DemoApp.scala)

Answer 1

我认为问题在于 Scala 脚本引擎实现了 Compilable ，但不是 Invocable ，这就是为什么你会得到一个类型转换异常。

无论如何，当您调用 eval在编译的结果上，你的代码被执行了，所以你不需要通过 Invocable 调用任何东西.

使用 asInstanceOf有点皱眉头，所以以下更惯用。

试试这个:

import java.io.FileReader
import javax.script._

object DemoApp extends App {
  // Get the Scala engine.
  val engine = new ScriptEngineManager().getEngineByName("scala")

  // See if the engine supports compilation.
  val compilerEngine = engine match {
    case c: Compilable => Some(c)
    case _ => None
  }

  // If the engine supports compilation, compile and run the program.
  val result = compilerEngine.map {ce =>
    val reader = new FileReader("src/main/scala/Demo.sc")
    ce.compile(reader).eval()
  }

  println(result.fold("Script not compilable")(_.toString))
}

或者，如果您只想让原始代码正常工作，您应该这样做:

import java.io.FileReader
import javax.script._

object DemoApp extends App {
  val engine = new ScriptEngineManager()
    .getEngineByName("scala")
    .asInstanceOf[ScriptEngine with Compilable]
  val reader = new FileReader("src/main/scala/Demo.sc")
  val result = engine.compile(reader).eval()
  // Output the result
  println(result.toString)
}