Classpath subtlety when using tomcat inside Eclipse

First, an eclipse dynamic web project only recognized classes produced by source folders configured in Java Build Path->Source and classes in the libraries under WebContent/WEB-INF/lib folder. The locations of source folders and class output folders do not matter if they are inside this project. The count of source folders and output folders also does not matter. By default, the output class folder is build/classes. It does not recognize the jar libraries which are not under WebContent/WEB-INF/lib and class folder configured in Java Build Path->Libraries. For class compilation, it is Ok. ClassNotFound exception will be thrown if you begin to use Run on server.