Tomcat

If you are going to serve only static(such as HTML) pages then Apache webserver would suffice but if the pages being (dynamically) served are in JSP/Servlet then you need a container that can interpret them, for which you can use Tomcat. Tomcat is a close relation of apache.

So if you see loads of Java processes open there a good chance tomcat is installed

Tomcat runs on port 8080 by default.

To check if your server is up and running correctly, use:
$ ps -ef | grep java | grep 8080

Logs are stored in /usr/local/jboss/server/default/log/

In some cases apache will be running and will redirect traffic to tomcat.