code: public void setLevel(String logger, Level level) {
        Logger log = getLogger(logger);
        log.setLevel(level);
        for (String loggerName : getLoggerNames()) {
           if (loggerName.startsWith(logger) && !loggerName.equals(logger)) {
              getLogger(loggerName).setLevel(level);
           }
        }
     }
docs: Sets the level of a logger
  
  @param logger The name of the logger to set the level for.
  @param level  The level to set the logger at