How to iterate through Java collection in Javascript

Question

I'm trying to do scripting with Javascript in a Java program. I haven't found a way to iterate through a Java collection in Javascript. If I call the iterator() method for the collection, I get the method names instead of the elements.

Here's a sample code:

function getValue(row, components) {
    var apartment = components.get(0);
    var rooms = apartment.getRooms();
    for (var room in rooms.iterator()) {
        println(room);
    }
    return rooms.toString();
}

The apartment.getRooms() returns a collection of rooms. When I study the value returned by this function, I know that its content are correct, but the values that get printed are the method names.

I invoke the Javascript from my Java program like this:

getInvocable().invokeFunction("getValue", row, components);

@TechExchange Why did you edit question? Are you sure collection is not java collection? — Mikita Belahlazau
– Mikita Belahlazau, Commented Jan 16, 2013 at 13:17
@user1983702 please post more code. What is getInvocable()? What libraries do you use? Edit your question — Mikita Belahlazau
– Mikita Belahlazau, Commented Jan 16, 2013 at 13:22

user1983702 · Accepted Answer · 2013-01-16 13:40:30Z

7

It seems that if I do the iteration as follows:

function getValue(row, components) {
    var apartment = components.get(0);
    var rooms = apartment.getRelated();
    for (var iterator = rooms.iterator(); iterator.hasNext();) {
        var room = iterator.next();
        println(room);
    }
    return rooms.toString();
}

It works.

answered Jan 16, 2013 at 13:40

user1983702

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6 Comments

soulcheck Over a year ago

if that worked you could probably try for (var room in rooms) as well

Mikita Belahlazau Over a year ago

Hm. Yes. As I know javascript's for in loop iterates through object properties. methods are also properties - then why you getting list of methods. I'm not sure for in loop works well with java collections.

soulcheck Over a year ago

@NikitaBeloglazov i was guessing, without knowing anything about the environment. What's treaten as properties when you're dealing with java objects in js? Everything? java properties with get/set? What about Maps?

Mikita Belahlazau Over a year ago

@soulcheck I checked and it seems it iterates through public methods and properties. For map it returned only all public methods without any data that contained in private properties.

soulcheck Over a year ago

@NikitaBeloglazov ah, ok. What env is that? rhino?

|

McDowell · Accepted Answer · 2013-01-17 21:35:05Z

4

To use for in you will have to convert it to an array first:

Collection<String> coll = Arrays.asList("foo", "bar", "baz");

String script = "var arr = coll.toArray();\n"
    + "for(var idx in arr) println(arr[idx]);\n";

ScriptEngine engine = new ScriptEngineManager()
    .getEngineByName("ECMAScript");
engine.getContext().setAttribute("coll", coll, ScriptContext.ENGINE_SCOPE);
engine.eval(script);

Otherwise you will iterate over the object properties.

If you are using Rhino 1.7 or above, you can use its non-standard iterator support:

for (i in Iterator(coll)) print(i);

edited Jan 17, 2013 at 21:35

answered Jan 16, 2013 at 13:48

McDowell

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