Put java class to nashorn's global scope

Question

I use sandboxed Nashorn like this:

ScriptEngine engine = new NashornScriptEngineFactory().getScriptEngine(
            new String[]{"--no-java", "--no-syntax-extensions", "--optimistic-types=true", "--language=es6"},
            null);

But I want to use a single particular class in my javascript. How to do that? For example, I have a class:

class MyClass
{
    public void m1()
    {
        System.out.println("This is m1");
    }
    public void m2()
    {
        System.out.println("This is m2");
    }
}

And I want to use it in the script like

let a=new MyClass();
a.m1();
a.m2();

How to do that? Thank you

Answer 1

you can use Bindings to provide java objects to the ScriptEngine:

import jdk.nashorn.api.scripting.NashornScriptEngineFactory;

import javax.script.Bindings;
import javax.script.ScriptEngine;
import javax.script.ScriptException;


public class MyClass {
    public static void main(String[] args) {

     ScriptEngine engine = new NashornScriptEngineFactory().getScriptEngine(
            new String[]{"--no-java", "--no-syntax-extensions", "--optimistic-types=true", "--language=es6"},
            null);

    Bindings bindings = engine.createBindings();
    bindings.put("myclass", new MyClass());
    engine.setBindings(bindings, ScriptContext.GLOBAL_SCOPE);

    String code = "myclass.m1();";

    try {
        engine.eval(code, bindings);
    } catch (ScriptException e) {
        e.printStackTrace();
    }
    }

    public void m1() {
        System.out.println("This is m1");
    }

    public void m2(String str) {
        System.out.println("This is m2 " + str);
    }

    public void m3(Class claz) {
        System.out.println(claz);
    }

}

or if MyClass really needs to be instantiated in the JS code you could do (works with Java >=9):

    Bindings bindings = engine.createBindings();
    bindings.put("myclass", StaticClass.forClass(MyClass.class));

    var code = "var a = new myclass(); a.m1();";

    try {
        engine.eval(code, bindings);
    } catch (ScriptException e) {
        e.printStackTrace();
    }