GZIPFilter is a project mainly written in Java, it's free.
The project is jspbook and I commit it to my repo.
This project is a GZIPFilter project. The project could compress all non-compressed web file, etc. ext-all.js or ext-all.css just add a filter like this:
<filter-mapping>
<filter-name>GZIPFilter</filter-name>
<url-pattern>*.js</url-pattern>
</filter-mapping>
That's ok, and you can see the firebug's output.
Please try it yourself.