Short PSA. If you want to set up Tomcat for debugging, set up JPDA.
To do so, simply open the startup.sh file, which is somewhere in TOMCAT/bin folder.
Add these two lines near the top
export JPDA_ADDRESS=7000 export JPDA_TRANSPORT=dt_socket
Then modify the exec line (usually the last line in the file) from this:
exec "$PRGDIR"/"$EXECUTABLE" start "$@"
exec "$PRGDIR"/"$EXECUTABLE" jpda start "$@"