Accessing java Maps & Lists as JavaScript Objects in Rhino

Take a look at RingoJS. It has convenient wrappers for list and map for Rhino such as this one

iterators seem to be the key!

if you want to iterate over all entries of a map, you could do the following

JAVA

//pass  the map and map.keySet().iterator() to the javascript
Object wrappedParameterMap = Context.javaToJS(parameterMap, scope);
ScriptableObject.putProperty(scope, "parameterMap", wrappedParameterMap);
Object wrappedParameterNames = Context.javaToJS(parameterMap.keySet().iterator(), scope);
ScriptableObject.putProperty(scope, "parameterNames", wrappedParameterNames);

JAVASCRIPT

while(parameterNames.hasNext()) {
  key = parameterNames.next();
  value = parameterMap.get(key);
}

https://developer.mozilla.org/en/New_in_Rhino_1.7R3#JS.c2.a0Objects_implement_Java_collections claims that JS objects resp. arrays can now be cast to Map resp. List, but this does not seem like it would work for your use case.

I had a similar problem that may be useful. I tried created native rhino objects and copied data into them.

Since Rhino 1.7.12 you can create ES6 lambdas and therefore create your own utility function like this:

function iterateMap(map, callback) {
    var iter = map.keySet().iterator();
    while(iter.hasNext()) {
        var key = iter.next();
        var value = map.get(key);
        callback(key, value);
    }
}

And then iterate like this

iterateMap(map, (key, value)=>{
    //...
});

The way to achieve this since Rhino 1.7.14 is to enable Context.FEATURE_ENABLE_JAVA_MAP_ACCESS.

This requires implementing a custom ContextFactory:

public class MyContextFactory extends ContextFactory {
    @Override
    protected boolean hasFeature(Context cx, int featureIndex) {
        switch (featureIndex) {
            case Context.FEATURE_ENABLE_JAVA_MAP_ACCESS:
                return true;
        }
        return super.hasFeature(cx, featureIndex);
    }
}

Then, this factory can be used to instantiate contexts that has this feature enabled:

Map<String, String> myMap = Map.of("message", "Hello from JavaScript");

ContextFactory ctxFactory = new MyContextFactory();
try (Context ctx = ctxFactory.enterContext()) {
    Scriptable scope = ctx.initSafeStandardObjects();
    ScriptableObject.putProperty(scope, "myMap", Context.javaToJS(myMap, scope));
    
    // Now map properties are accessible via `[key]` or `.key`:
    Object result = ctx.evaluateString(scope, "myMap.message", "<sample>", 1, null);
    String message = Context.jsToJava(result, String.class);
    System.out.println(message); // prints "Hello from JavaScript"
}