Tomcat is a per-requiisite. To be precise, the requirement is for a servlet engine, and Apache HTTP server is not one.
Note that Tomcat can be installed and configured to run "behind" the Apache HTTP server, so that the HTTP server answers requests from the network, and forwards certain requests to Tomcat and thereby the Tersus server and application. See http://tomcat.apache.org/connectors-doc/webserver_howto/apache.html for details.
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