This week's book giveaway is in the Java in General forum. We're giving away four copies of Think Java: How to Think Like a Computer Scientist and have Allen B. Downey & Chris Mayfield on-line! See this thread for details.
The classpath for a web app is (at least)
plus all the JARs in the WEB-INF/lib/
In addition, servers may add further directories to the classpath to give access to shared resources between web apps and provid system / server resources.