Subj : RE: Integrating Java Maps  in Rhino
To   : netscape.public.mozilla.jseng
From : Rod Macpherson
Date : Sat May 14 2005 03:07 pm


I started off wading through NativeJavaObject which as you know is a
full-on reflection of an arbitrary object. Separating the wheat from the
chaff was a little rough so I put that aside and started with a clean
implementation of Scriptable (plus Wrapper) with all of the methods
stubbed out. 

The Scriptable interface does a good job of spelling out the
requirements. After implementing the WrapperFatory.wrapAsJavaObject
override to test for Map instances, everything worked as advertised. 

I think I understand why they did not include this in the core. If they
did then anybody trying to use Map or Collection as a POJO would be
thwarted and there are many different ways to expose these classes to
JavaScript.

Thanks for the helpful hints. 

-----Original Message-----
From: Jan Grant [mailto:Jan.Grant@bristol.ac.uk] 
Sent: Wednesday, May 11, 2005 6:58 AM
To: Rod Macpherson
Cc: mozilla-jseng@mozilla.org
Subject: RE: Integrating Java Maps in Rhino

On Wed, 11 May 2005, Rod Macpherson wrote:

> Here is another way of stating the problem. 
> 
>  
> 
> We can dynamically add properties to a JavaScript object at will. How
> can we translate the key/value pairs in a Java Map to a set of
> properties on a JavaScript Object? The objective being the ability to
> use foo.bar syntax in JavaScript versus foo.get( "bar" ).

This is reasonably doable.

Look at org.mozilla.javascript.WrapFactory: in particular, 
wrapAsJavaObject.

This is called to wrap java objects that don't fall into other 
categories that are already special-cased, and just slaps a 
NativeJavaObject around.

You can subclass the WrapFactory and override this method; then install 
the result using org.mozilla.javascript.Context
#setWrapFactory(WrapFactory)

A NativeJavaMap implementation is pretty straightforward: see 
NativeJavaObject for hints, and the Rhino documentation on java host 
objects: there are only a few methods you need to implement, since a 
java Map is very close indeed to a javascript object.

(The trick is to remember to wrap objects on the way out of the map, and

to unwrap them on the way back in.)

Hope this is a sufficient pointer (don't have time to write the code 
right now) -

Cheers,
jan

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44 (0)117 9287088 (with luck)   http://ioctl.org/jan/
It's a sad fact that the word "semantics" seems to have lost all
meaning.

.