private void loadBackupFiles() {
      logger.info("Loading mysql monthly storage usage backup file from directory {}", backupDirPath);
      File backupDir = backupDirPath.toFile();
      // First remove all the temp files
      FileFilter tempFileFilter = (File pathname) -> tempFilenamePattern.matcher(pathname.getName()).matches();
      File[] files = backupDir.listFiles(tempFileFilter);
      if (files != null) {
        for (File file : files) {
          logger.trace("Delete temp file {}", file.getName());
          tryDeleteFile(file.toPath());
        }
      }

      // Then add all the files
      FileFilter fileFilter = (File pathname) -> filenamePattern.matcher(pathname.getName()).matches();
      files = backupDir.listFiles(fileFilter);
      if (files != null) {
        for (File file : files) {
          backupFiles.add(file.getName());
        }
      }
      logger.info("Loaded {} backup files", backupFiles.size());
      logger.trace("Backup files {}", backupFiles);
    }
Load all the backup files under the backup directory to a list.
ambry-quota/src/main/java/com/github/ambry/quota/storage/MySqlStorageUsageRefresher.java