code: public void setFilename(String filename)
      {
          if (filename!=null)
          {
              filename=filename.trim();
              if (filename.length()==0)
                  filename=null;
          }
          _filename=filename;        
      }
docs: Set the log filename.
  @see NCSARequestLog#setRetainDays(int)
  @param filename The filename to use. If the filename contains the
  string "yyyy_mm_dd", then a RolloverFileOutputStream is used and the
  log is rolled over nightly and aged according setRetainDays. If no
  filename is set or a null filename
  passed, then requests are logged to System.err.