在 Java 程序中编译和运行 Scala 文件

Question

I am working on a Java program that takes a Scala program in a text file, compiles it (inside Java), then runs it (also inside Java). I could not figure out a clean way to implement this. To compile, I tried to use code as shown below:

import scala.collection.JavaConversions;
import scala.tools.nsc.Global;
import scala.tools.nsc.Settings;

Global g = new Global(new Settings());
Global.Run run = g.new Run();
List<String> fileNames = new ArrayList<String>(Arrays.asList("Hello.scala"));

run.compile(JavaConversions.asScalaBuffer(fileNames).toList());

However, I get an error (reduced for clarity):

error: error while loading Object, Missing dependency 'object scala in compiler mirror', required by C:\Program Files\Java\jdk1.7.0_79\jre\lib\rt.jar(java/lang/Object.class)

I did not understand what was causing this or how to fix. As a temporary workaround, I tried compiling the Scala code externally and calling that in Java via:

Runtime rt = Runtime.getRuntime();
Process pr = rt.exec("java -cp scala-library.jar;. Hello");

While I think the code runs, it is not interactive with the Java program as I would like. For example, when running the Scala program (inside Java) if the Scala program wanted the user to type a string into the console, the Java program should do the same essentially.

Any guidance is appreciated.

Answer 1

The easiest way is probably just to use a tiny wrapper library that takes care of things like class-paths etc. For example, there is a small library Twitter Util-Eval ( source ).

Here is an example:

package foo;

import com.twitter.util.Eval;

public class Test {
  public static void main(String[] args) {
    final Eval eval = new Eval();
    final int result = eval.apply("3 + 4", true);
    System.out.println("Result: " + result);
  }
}

---

If you want to bake your own compiler and runner wrapper, this involves a bit more, you will need to compile to virtual files and then load them into a class loader (see for example here and here ).