public interface IndexExportFormatter {

    /**
     * Returns the file extension for this format (e.g. ".html", ".json").
     *
     * @return the file extension including the leading dot
     */
    String getFileExtension();

    /**
     * Returns the default index file name for this format (e.g. "index.html", "index.json").
     *
     * @return the index file name
     */
    String getIndexFileName();

    /**

    /**
     * Creates a new HtmlIndexExportFormatter instance.
     */
    public HtmlIndexExportFormatter() {
        // default constructor
    }

    @Override
    public String getFileExtension() {
        return ".html";
    }

    @Override
    public String getIndexFileName() {
        return "index.html";
    }

    @Override

    /**
     * Creates a new JsonIndexExportFormatter instance.
     */
    public JsonIndexExportFormatter() {
        // default constructor
    }

    @Override
    public String getFileExtension() {
        return ".json";
    }

    @Override
    public String getIndexFileName() {
        return "index.json";
    }

    @Override

         * The checksum extension SHOULD NOT contain dot (".") character.
         * Example: "sha1".
         */
        @Nonnull
        String getFileExtension();

        /**
         * Each invocation of this method returns a new instance of calculator, never {@code null} value.
         */
        @Nonnull
        ChecksumCalculator getCalculator();
    }

    assertThat(Files.getFileExtension(".")).isEqualTo("");
    assertThat(Files.getFileExtension("..")).isEqualTo("");
    assertThat(Files.getFileExtension("...")).isEqualTo("");
    assertThat(Files.getFileExtension("blah")).isEqualTo("");
    assertThat(Files.getFileExtension("blah.")).isEqualTo("");
    assertThat(Files.getFileExtension(".blah.")).isEqualTo("");

    assertThat(MoreFiles.getFileExtension(root())).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath(".."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("..."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("blah"))).isEqualTo("");

    assertThat(MoreFiles.getFileExtension(root())).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath(".."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("..."))).isEqualTo("");
    assertThat(MoreFiles.getFileExtension(FS.getPath("blah"))).isEqualTo("");

   * href="https://learn.microsoft.com/en-us/archive/blogs/askcore/alternate-data-streams-in-ntfs">Alternate
   * Data Streams</a>.
   *
   * @since 11.0
   */
  public static String getFileExtension(String fullName) {
    checkNotNull(fullName);
    String fileName = new File(fullName).getName();
    int dotIndex = fileName.lastIndexOf('.');
    return (dotIndex == -1) ? "" : fileName.substring(dotIndex + 1);

                return Paths.get(exportPath, "_invalid", hashString(url) + formatter.getFileExtension());
            }
            return resolved;
        } catch (final Exception e) {
            logger.debug("Failed to parse URL: {}", url, e);
            return Paths.get(exportPath, "_invalid", hashString(url) + formatter.getFileExtension());
        }
    }

    private String hashString(final String input) {

   * filesystem due to NTFS's <a
   * href="https://learn.microsoft.com/en-us/archive/blogs/askcore/alternate-data-streams-in-ntfs">Alternate
   * Data Streams</a>.
   */
  public static String getFileExtension(Path path) {
    Path name = path.getFileName();

    // null for empty paths and root-only paths
    if (name == null) {
      return "";
    }

    String fileName = name.toString();