appender.setMaxFileSize(DEF_APPENDER_MAXFILESIZE);
appender.setMaxBackupIndex(DEF_APPENDER_MAXBACKUP);
PatternLayout layout = new PatternLayout(DEF_APPENDER_PATTERN);
appender.setLayout(layout);
appender.setFile(filename);
appender.activateOptions();
//add into the logger
logger.addAppender(appender);
}
//keep the logfile name