One way to start the tomcat on the startup is to run it using croncron using the @reboot@reboot attribute:
open up a terminal and type :
sudo crontab -e
at the end of the file enter the command:
@reboot /`PATH_TO_WHERE_TOMCAT_INSTALLED`/bin/startup.sh
@reboot PATH_TO_WHERE_TOMCAT_INSTALLED/bin/startup.sh
save the file and exit.
The above command will run the command once everytime computer boots up.