Nashorn two-way binding

Script.java

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.lang.reflect.InvocationTargetException;

public class Script {

    public static void main(String... args) throws ScriptException, IllegalAccessException, InvocationTargetException, InstantiationException {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        engine.eval("" +
                        "var Integration = Java.type('Script.Integration');\n" +
                        "var intObject = new Integration();\n" +
                        "print('SCRIPT Return from echo: ' + intObject.echo('Hello world'));\n" +
                        "intObject.info('someInfo');\n" +
                        "intObject.callback = function(name,info){print('SCRIPT callback{name:\"'+name+'\",info:\"'+info+'\"}')}\n" +
                        "intObject.info('someInfo');\n"
        );
    }

    public static class Integration {
        Callback callback;
        String info;

        public String echo(String out) {
            System.out.println("JAVA echo");
            return out;
        }

        public void info(String info) {
            System.out.println("JAVA setInfo");
            this.info = info;
            if (callback != null) {
                callback.onEvent("callback method", info);
            } else {
                System.out.println("JAVA No callback registered");
            }
        }

        public void setCallback(Callback callback) {
            System.out.println("JAVA setCallback");
            this.callback = callback;
        }

        public Callback getCallback() {
            System.out.println("JAVA getCallback");
            return callback;
        }
    }

    @FunctionalInterface
    public interface Callback {
        public abstract void onEvent(String name, String param);
    }
}