// if the file is empty, the archiver prints an
// exception, so protect against that case and
// return null without updating either cache
if (stream.available() > 0)
{
XMLInputStream xmlInput = new XMLInputStream(stream,
getClass().getClassLoader());
mappingClass =
(MappingClassElement)xmlInput.readObject();
xmlInput.close();
// postUnarchive performs version number checking
// and possible format conversions
mappingClass.postUnarchive();