StorageService.java

  public Mono<Blob> save(final FilePart filePart) {
    final var storageUUID = UUID.randomUUID();
    final var uploadDir = new File(UPLOAD_DIR + storageUUID);

    return filePart.transferTo(uploadDir).flatMap(unused -> {
      final var blobb = Blob.builder()
          .uuid(storageUUID)
          .originalFileName(filePart.filename())
          .extension(getExtension(filePart.filename()).orElse(null))
          .build();
      return blobRepository.save(blobb);
    });
  }