A Loader represents a Java ClassLoader implementation that can
be used by a Container to load class files (within a repository associated
with the Loader) that are designed to be reloaded upon request, as well as
a mechanism to detect whether changes have occurred in the underlying
repository.
In order for a Loader implementation to successfully operate
with a Context implementation that implements reloading, it
must obey the following constraints:
Must implement Lifecycle so that the Context can indicate
that a new class loader is required.
The start() method must unconditionally create a new
ClassLoader implementation.
The stop() method must throw away its reference to the
ClassLoader previously utilized, so that the class loader,
all classes loaded by it, and all objects of those classes, can be
garbage collected.
Must allow a call to stop() to be followed by a call to
start() on the same Loader instance.
Based on a policy chosen by the implementation, must call the
Context.reload() method on the owning Context
when a change to one or more of the class files loaded by this class
loader is detected.