Getting field values of a javascript object

Question

I've been using rhino to allow the customization of some applications. Here is an example of JavaScript function that is called from Java:

        function() {
            var phone = this.telephoneNumber;
            phone = phone.replace(/[^+0-9]/g,"");
            if (phone.indexOf("+") == 0) {
                phone = "00" + phone.substring(1);
            }
            if (phone.indexOf("0041") == 0) {
                phone = "0" + phone.substring(4);
            }
            if (phone.indexOf("0") == 0) {
                phone = "0" + phone;
            }
            return {
                Name: this.sn + " " + this.givenName,
                firstName: this.givenName || "",
                lastName: this.sn || "",
                phone: phone,
                service: "",
                info: ""
            };
        }

The java application can then get the values of the returned object for whatever it needs to do.

Now that rhino is part of the JVM, I would like to use the scripting API instead of the Rhino API, but I haven't found how to get the field values of a JavaScript object from Java code.

Rhino is not part of the JVM; it's part of the runtime. It's like how Java just uses a patched version of Xalan for XSLT. You're not going to get any significant improvements in performance unless they heavily optimized the version of Rhino in the runtime, but failed to contribute the optimizations back to Rhino. Moreover, you're getting an old version of Rhino. — David Ehrmann
– David Ehrmann, Commented May 26, 2014 at 6:46
@DavidEhrmann Yes, the objective is not to get performance improvements, but to use the standard script engine API, so that switching to another script language would be easier. — Maurice Perry
– Maurice Perry, Commented May 26, 2014 at 7:12

David Ehrmann · Accepted Answer · 2014-05-26 07:45:04Z

1

+50

This loosely couples the scripting language, but with the caveats that the functions need to be named, and the returned object needs to be a Map (Rhino does this, but I'm not sure about JRuby).

    ScriptEngineManager factory = new ScriptEngineManager();
    ScriptEngine engine = factory.getEngineByName("JavaScript");
    engine.eval("function x() { return { foo: 10 } }");

    Object o = ((Invocable)engine).invokeFunction("x");
    if (o instanceof Map) {
    Map m = (Map<Object, Object>)o;
        System.out.println(m.get("foo"));
    }

or

    CompiledScript script = ((Compilable)engine).compile("(function() { return {bar:20} })()");
    System.err.println(((Map)script.eval()).get("bar"));

But you have to cheat and call your function by padding it with (...)().

edited May 26, 2014 at 7:45

answered May 26, 2014 at 7:32

David Ehrmann

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3 Comments

Maurice Perry Over a year ago

Fair enough. It only works with 1.7+ though... I guess it's time to stop supporting older versions... Funny detail: 1.7 returns a Double whereas 1.8 returns an Integer.

David Ehrmann Over a year ago

You should be able to run it in Java 6 if you find the approriate JSR JAR. I remember having to do that with StAX and Java 5. Interesting find with the double. Javascript numbers are technically all doubles, so I suppose it makes sense. When you type check, be sure to use Number, then intValue().

Maurice Perry Over a year ago

Well it works with java 6, except that the object is not a Map.

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