code: @Override
      public synchronized void shutdown() {
          try {
              if (open) {
                  open = false;
                  FileWriter logWriter = new FileWriter(logFile);
                  logWriter.write(buffer.toString());
                  logWriter.close();
              }
          } catch (IOException e) {
              logger.error("Error shutting down", e);
          }
      }
docs: On the first call to this method, write the buffer to the log file. Set
  the flag so no more logging calls will be accepted.