I'm writing some code that requires a configuration file to be edited by
the end user.  The end user may also provide classes for describing
problems to be solved by the software.  There are a number of such classes
describing problems and algorithms already provided.  I would like the end
users to be able to use custom configuration options in the same file that
the system configuration options are provided.  

This works fine with properties files, but then I have to have generic
methods to get the properties back, things like getConfigurationInt().
This is a bit annoying and looks bad in the code.  One would prefer that
the user be able to register their own properties to be retrieved and the
defaults for these properties, and even possibly the method names to get
and set them.  One would also wish to be able to print out a file that
includes all the properties that are in use by the program including those
that are not set, but defaulted.  The idea being that one would be able to
duplicate the run at some future date by using the resulting configuration
file, or understand exactly what options the user had when using the
program.  

There are other problems too.  Ideally this would all be easy to use in
testing.  Right now I have a singleton class that wraps around the
properties and provides getters and setters for some of them.  It just
doesn't work well for testing.  

So some framework that would ease testing would be preferred.  

Is there something out there that I might want to try?  

Any ideas?  

Thanks.