Nashorn JavaScript Invocable.getInterface在Web应用程序中的类加载器中失败

Question

I need to invoke (with Nashorn) from Java code a function defined in JavaScript and to pass there some parameters. Instead of using Invocable.invokeFunction("Foo", arg1, arg2), I was going to define an interface, then request Invocable to produce its implementation, just like Oracle suggests here , "Embedding Oracle Nashorn":

package mypackage;
public final class MyClass {
  public interface Composer {
    void compose(final StringBuilder subject, final StringBuilder body);
  }

  public void composeEmail(...) {
      ...
      final ScriptEngineManager engineManager = new ScriptEngineManager();
      final ScriptEngine engine = engineManager.getEngineByName("nashorn");
      engine.eval(scriptText);
      final Invocable invocable = (Invocable) engine;
      final Composer composer = (Composer)invocable.getInterface(Composer);
      composer.compose(subject, body);
      ...
  }
}

Problem is, since I am doing this in a web application running in Tomcat, my Composer gets loaded by app-level classloader, while nashorn classes were loaded by extensions class loader. So getInterface fails saying a TypeError: Can not find a common class loader for ScriptObject and mypackage.Composer

Any ideas how to overcome that? I could, of course, try to load Composer in a parent classloader, in an assumption (hack-like) that it is actually an ext loader, but there is at least one problem with that: it cannot find my class. I suppose it's quite right: my package resides in my web application, and extension loader does not look there. Any other great ideas?

PS And now I noticed that this message is weird: if an app classloader delegates to ext classloader, then of course the latter is the common classloader for them. Maybe they were trying to say that the target interfaces's classloader must be equal to actual implementation's classloader, or the implementation's classloader must delegate to the target's (but not vice versa)?

Answer 1

直接创建jdk.nashorn.api.scripting.NashornScriptEngineFactory的实例而不是执行engineManager.engineByName() ，然后通过调用NashornScriptEngineFactory.getScriptEngine(ClassLoader appLoader)并将其传递给应用程序级加载器来创建ScriptEngine 。