The Resources element represents the web
  application static resources, from which classes will be loaded,
  HTML, JSP and the other static files will be served. This allows the webapp
  to reside on various mediums other than the filesystem, like compressed
  in a WAR file, in a JDBC database, or in a more advanced versioning
  repository.
  A unified caching engine is provided for all accesses to the webapp
  resources made by the servlet container and web applications which use the
  container provided mechanisms to access such resources, such as classloader
  access, access through the ServletContext interface, or native
  access through the DirectoryContext interface.
  Note: Running a webapp with non-filesystem based
  Resources implementations is only possible when the webapp does not
  rely on direct filesystem access to its own resources, and uses the methods
  in the ServletContext interface to access them.
  A Resources element MAY be nested inside a
  Context component.  If it is not included,
  a default filesystem based Resources will be created automatically,
  which is sufficient for most requirements.