There seems to be an omission in the instructions for setting up Joseki on Tomcat. Link here
In the JBoss section there is mention of ojdbc6.jar, that has to be copied someplace. I had to copy same file to a Tomcat "lib" folder either in the tomcat installation folder, or in the tomcat instance folder. In retrospect I see why this is so, but I think it would be appropriate with a hint on the step-by-step instructions.