>>why u want to set virtual host for tomcats
I use it because it works, but I wonder if there is another way.

Virtual Hosts are described in the web site you suggested to me,
see '6. Configuring Private JVMs' at http://raibledesigns.com/tomcat/index.html

Like you I use the mod_jk.dll but I have never heard of "channel sockets".
can you describe this channelsocket method?

Apache, the web server holds the static web pages. Tomcat, the servlet container, holds the webapps. The only way for the user to reach the webapps is to have them defined in the Apache conf as Virtual Hosts.
If not how are they linked to the webserver?
Do your Tomcats also work as webservers at 8080?