@Override
          public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
              throws IOException {
            if (SnapshotFileSet.isDataFile(file.toFile())) {
              fileList.add(file.toFile());
            }
            return FileVisitResult.CONTINUE;
          }
Search all data files in one directory recursively.

@return
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/snapshot/SnapshotLoader.java