using System properties in application vs. Singleton class?

[bb]

What are the advantages and/or disadvantages in using
System.setProperties(map) for values read from an xml config file for
'global' use in an application vs. creating a Singleton class to store
the same values? I've gone the Singleton route in the past but I'm not
totally clear on the difference with System.properties . The values
will be read-only after they are read from the config file.

Thanks,
Bill