liang, You should try two things to get the desired result. First, setup a welcome-file in your web.xml to remove the aaa.do. Then, configure jk2 (a webserver-to-webappserver connecter) to change http://www.aaaaa.com/web/ to http://www.aaaaa.com/.
Shed's tip about configuring jk2 only works if you have an Apache HTTP server in front of your web container. Also, adding a welcome file into your application's web.xml or configuring a servlet filter doesn't help unless your application is mapped to the "default context" of your container.
Could you describe what kind of server setup you're using? [ May 21, 2004: Message edited by: Lasse Koskela ]