- WEB-INF/classes/ (.class files go here)
- WEB-INF/lib/ (.jar files go here)
- External Libraries (only for apps with SE Extensions enabled)
- The main SE classpath (-classpath argument passed to the JVM (this is visible on the Classpath page of the SE admin UI)
- The JVM's boot classpath, extensions folder, & endorsed folder
as mentioned here
(check your JVM documentation to learn in what order the JVM searches those locations).