||Utility class that represents either an available "Optional Package"
(formerly known as "Standard Extension") as described in the manifest
of a JAR file, or the requirement for such an optional package.
||Subclass implementation of java.net.URLClassLoader that knows how
to load classes from disk directories, as well as local and remote JAR
||Specialized web application class loader.
||Classloader implementation which is specialized for handling web
applications in the most efficient way, while being Catalina aware (all
accesses to resources are made through the DirContext interface).