Code splitting in cross domain GWT components

I just upgraded to GWT 2.1.  Lots of new features, though they are mostly aimed at building webapps (as opposed to enhancing websites).

The upgrade process was pretty painless.  A couple of notable changes (for my app):

• <code>DeferredCommand</code> has been deprecated, and replaced with <code>Scheduler.get().scheduleDeferred</code>.  However, the API didn’t really change all that much, so this update is a simple search and replace (looks like the documentation has not yet been updated).
• <code>HTTPRequest.getAsync</code>, which has been deprecated for years, finally disappeared.

The big win for me was code splitting when using the cross site (xs) linker.  This means that code served from one host can run on other domains and can include code splitting in the same manner as code that runs on the original host.

Why is this a big deal?  Two of our key widgets run on both our main host and subsidiary hosts.  These widgets are relatively complex, and it would be great for performance to split out that code so it wouldn’t be loaded on pages where it wasn’t shown.  This wasn’t really possible before GWT 2.1.  I’m still in the process of putting in the code split calls, but will let you know what the savings are when I’m done.

Update Jan 8, 2011: I was able to cut about 18% off the initial and leftover code download size.