I have tomcat running on port 8080 and want a particular URL, lets say
http://example.com/app, to actually point to
I have other content on the website that should remain unchanged.
It sounds like what you want is not a redirect but actually a proxy. Check out the information found in the mod_proxy config page. You should end up with something like:
ProxyPass /app http://example.com:8080/app ProxyPassReverse /app http://example.com:8080/app