code: public static boolean isUptodate( PlexusIoResource source, long destinationDate )
      {
          final long s = source.getLastModified();
          if ( s == PlexusIoResource.UNKNOWN_MODIFICATION_DATE )
          {
              return false;
          }
  
          if ( destinationDate == 0 )
          {
              return false;
          }
  
          return destinationDate > s;
      }
docs: Queries, whether the given source is up-to-date relative to
  the given modification date.