Theoretically, you could deploy your application entirely on Tomcat. In fact, for low volume sites, this is entirely appropriate. For one of several reasons, however, you might want to layer Tomcat under Apache. These reasons are as follows:
To offload the mundane serving of static pages and images to the more efficient Apache server
Because you want to host sites under several virtual hostnames
Because you want to use SSL
Integrating Apache and Tomcat is fairly simple, if you follow the rules. First, you will need a copy of Apache for your architecture. If you're running Linux, you might already have it installed; otherwise, you can grab an RPM from one of the many sources on the Web (including www.apache.org) and install ...