如何解决为什么我的重写规则没有被apache应用？

I've got a tomcat 6 web app running with apache httpd as the front end. I'm using mod_proxy and mod_proxy_ajp to forward the requests to tomcat. My server is running ubuntu. Now I'm trying to use mod_rewrite to remove the leading www, so that my canonical website url is I've got a tomcat 6 web app running with apache