출처 : http://tomcat.apache.org/tomcat-8.0-doc/class-loader-howto.html

      Bootstrap
          |
       System
          |
       Common
       /     \
  Webapp1   Webapp2 ...

Therefore, from the perspective of a web application, class or resource loading looks in the following repositories, in this order:

• Bootstrap classes of your JVM
• /WEB-INF/classes of your web application
• /WEB-INF/lib/*.jar of your web application
• System class loader classes (described above)
• Common class loader classes (described above)