I already now how to deploy a Java web application (and who doesn't?) but I'm looking to be a Tomcat power user/admin.
Stuffs like monitoring Tomcat, dumbing Tomcat heap, solving runtime errors and other tricks.
Where to start? any resources and tools?
Ah, grasshopper, but you you know all the ways to deploy a Java web application?
#1 place to obtain knowledge is the documentation at tomcat.apache.org.
From there, you can work you way to becoming expert in the various testing and measuring tools. These come from various sources and include things like Cactus and JMeter. A lot of that stuff is not Tomcat-specific, or even J2EE-specific. Some of my best metrics come from the Firebug browser plug-in.
Obviously it pays to develop expertise in the general care and tuning of JVMs themselves, using stuff like JMS, the management EJB and jconsole.
For the really dirty stuff, be wise in the ways of logging and developing internal metric and diagnostic code.
Then there's clustering and High Availability
In the Real World, you'll probably need to learn about how to link Apache or IIS to Tomcat - what the options are and how to use them effectively.
Never hurts to know about networking in general, and DNS in particular.
And, of course, when you get bored, you can always read the Tomcat source code!
An IDE is no substitute for an Intelligent Developer.