How to unbox values returned by javascript (nashorn) in Java object?

Question

I have the following program, which executes Javascript in Java (nashorn) . The Javascript code is returning an object.

public Object execute(){
        ScriptEngineManager sem = new ScriptEngineManager();
        ScriptEngine e = sem.getEngineByName("nashorn");  
        Invocable invocable = (Invocable)e;
        ScriptEngineFactory f = e.getFactory();
        Object result;
        try {
            String statement = "function fetch(value, count) { count++ ; return {'value': value,'count' : count} }; } ; ";
            CompiledScript cs = ((Compilable)e).compile(statement);
            cs.eval();
            result = invocable.invokeFunction("fetch", 10,2);

        }   
        catch (Exception se ) {
            String version = System.getProperty("java.version");
            System.out.println(version);
            result = "script exception ";
        }

How do I access the object values in my result object in Java? Initially, I tried using result.toString() to get results. Seems to return [Object Object]

Is there a way, where I could return the results to result object such that I could get values equivalent to result.value , and result.count (similar to Javascript) .

Answer 1

You don't return a JSObject from the JavaScript function. Valid would be

{
  value: value,
  count : count
}

So you could use this Java code.

package de.lhorn.so;

import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import jdk.nashorn.api.scripting.JSObject;

public class SOPlayground {

    public static void main(String[] args) throws Exception {
        SOPlayground sop = new SOPlayground();
        JSObject jso = sop.execute();
        System.out.println("value=" + jso.getMember("value"));
        System.out.println("count=" + jso.getMember("count"));
    }

    public JSObject execute() throws ScriptException, NoSuchMethodException {
        final ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        final Compilable compilable = (Compilable) engine;
        final Invocable invocable = (Invocable) engine;

        final String statement =
          "function fetch(value, count) { count++ ; return {value: value, count : count} };";
        final CompiledScript compiled = compilable.compile(statement);

        compiled.eval();

        return (JSObject) invocable.invokeFunction("fetch", 10, 2);
    }
}

Output:

value=10
count=3.0

Answer 2

If the return value of your program is a JavaScript object, you should be able to cast it to jdk.nashorn.api.scripting.JSObject in Java and then use its methods (e.g. getMember()) to query and manipulate it.