start tomcat using the following command
$CATALINA_HOME/bin/catalina.sh jpda start
then in Eclipse, Click Debug->Debug Configurations
Add a new Remote Java Application, and put in the IP and port. The defaults will work (localhost 8000) in a simple development environment.
Switch the to debug perspective, you can see the threads, and you can set breakpoints by dbl clicking line numbers. When the code is executed Eclipse will alert you. You can then step code, inspect variables, etc
