hosting sub-domain to domain root in tomcat

Question

I have a domain(exmaple.com) and work correctly.
I want to hosting another sub-domain(sub.exmaple.com) to domain(example.com) in tomcat.
sub-domain and domain hosting to single app(directory) in tomcat.

I set server.xml with following:

 <Host name="example.com"  appBase="site"
        unpackWARs="true" autoDeploy="true"></host>

 <Host name="sub.example.com"  appBase="site"
        unpackWARs="true" autoDeploy="true"></host>

example.com working but sub.example.com not working.