How to convert Rhino-JavaScript arrays to Java-Arrays

I'm not sure if it was the case when this question was first asked, but NativeArray implements the java.util.List interface. A simple way to convert to a real Java array is therefore:

Object[] array = ((List<?>) result).toArray();

If the Javascript is under your control, you could do the transformation there, as per this document. So to adapt your example, something like:

ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine jsEngine = mgr.getEngineByName("JavaScript");
jsEngine.eval("function getArray() {return [1,2,3,4,5];};");
String convertFuncSrc =
     "function convertArray(type, arr) {"
   + "  var jArr = java.lang.reflect.Array.newInstance(type, arr.length);"
   + "  for (var i = 0; i < arr.length; i++) { "
   + "    jArr[i] = arr[i];"
   + "  }"
   + "  return jArr;"
   + "};";
jsEngine.eval(convertFuncSrc);
Object result = jsEngine.eval("convertArray(java.lang.Integer.TYPE, getArray());");
int[] javaArray = (int[])result;

Although, if you can't change the Javascript this approach won't work, and you [i]will[/i] have an instance of sun.org.mozilla.javascript.internal.NativeArray as your result variable. At which point I think you just need to cast and deal with it directly, using whatever public methods it exposes; it's probably not pretty but I don't see any other options. In particular I think the only thing you can guarantee at the nice Rhino level is that it will be an instance of Scriptable (and probably ScriptableObject), which doesn't help you use it as an Array.

Kevin's answer looks like a good way to go here (and is similar to what I was just about to edit in! :-))

In my case I wanted to produce a Java array within the script. (This use case also matches the question.)

Following Creating Java Arrays, I came up with

var javaArray = java.lang.reflect.Array.newInstance(java.lang.Integer, jsArray.length);
for (var i = 0; i < javaArray.length; i++) {
  javaArray[i] = new java.lang.Integer(jsArray[i]);
}

General solution using JASON as data intermediate:

Object result = jsEngine.eval("JSON.stringify(getArray())");    
JsonReader jsonReader = Json.createReader(new StringReader(result.toString()));
JsonArray jsonArray = jsonReader.readArray();
jsonReader.close();
int[] numbers = new int[jsonArray.size()];
int index = 0;
for(JsonValue value : jsonArray){
    numbers[index++] = Integer.parseInt(value.toString());
}