TwelveMonkeys: Unable to modify a JPEGImage10Metadata comment value

I am trying to modify the JFIF comment (note: not an EXIF tag, but the comment in the JFIF metadata) of an image and am running into the issue that the JPEGImage10Metadata object is readonly.

I am trying the approach of getting the metadata as a tree, walking the tree, replacing an attribute and setting the metadata as a tree, as outlined here: https://stackoverflow.com/a/9508479

Is there another way?

I have looked for ways to copy-and-mutate the JPEGImage10Metadata object, but not found any?

(I can see the existing value in the debugger so that it feels kind of annoying not to be able to change it… I’ve even considered using reflection… 😄 )

Here is the code that I’m trying to run:

    File downloadImageUrlToTempFile(AlbumEntry albumEntry, Path tempDir) {
        var imageUrl = albumEntry.getImageUrl();
        if (imageUrl == null || imageUrl.isEmpty()) {
            throw new OldAlbumException(String.format("Unable to download album entry matching id=%d, imageUrl is missing", albumEntry.getId()));
        }

        var fileName = findFileNamePartOfUrl(imageUrl);
        var tempfile = tempDir.resolve(fileName).toFile();
        IIOImage image = null;
        ImageWriter writer = null;
        try {
            HttpURLConnection connection = getConnectionFactory().connect(imageUrl);
            connection.setRequestMethod("GET");
            try(var inputStream = ImageIO.createImageInputStream(connection.getInputStream())) {
                var readers = ImageIO.getImageReaders(inputStream);
                if (readers.hasNext()) {
                    var reader = readers.next();
                    writer = ImageIO.getImageWriter(reader);
                    reader.setInput(inputStream);
                    image = reader.readAll(0, null);
                }
            }
        } catch (IOException e) {
            throw new OldAlbumException(String.format("Unable to download album entry matching id=%d from url=\"%s\"", albumEntry.getId(), albumEntry.getImageUrl()), e);
        }

        var metadata = image.getMetadata();
        var metadataAsTree = metadata.getAsTree("javax_imageio_1.0");
        findJfifCommentNode(metadataAsTree)
            .ifPresent(node -> node.setAttribute("value", albumEntry.getDescription()));
        try {
            metadata.setFromTree("javax_imageio_1.0", metadataAsTree);
        } catch (IIOInvalidTreeException e) {
            throw new OldAlbumException(String.format("Failed to replace comment in local copy of album entry matching id=%d from url=\"%s\"", albumEntry.getId(), albumEntry.getImageUrl()), e);
        }

        try (var outputStream = ImageIO.createImageOutputStream(new FileOutputStream(tempfile))){
            writer.setOutput(outputStream);
            writer.write(image);
            Files.setLastModifiedTime(tempfile.toPath(), FileTime.from(albumEntry.getLastModified().toInstant()));
            return tempfile;
        } catch (IOException e) {
            throw new OldAlbumException(String.format("Unable to save local copy of album entry matching id=%d from url=\"%s\"", albumEntry.getId(), albumEntry.getImageUrl()), e);
        }
    }

    Optional<IIOMetadataNode> findJfifCommentNode(Node metadataAsTree) {
        return StreamSupport.stream(iterable(metadataAsTree.getChildNodes()).spliterator(), false)
            .filter(n -> "Text".equals(n.getNodeName()))
            .findFirst()
            .flatMap(n -> StreamSupport.stream(iterable(n.getChildNodes()).spliterator(), false).findFirst());
    }

    public static Iterable<IIOMetadataNode> iterable(final NodeList nodeList) {
        return () -> new Iterator<IIOMetadataNode>() {

                private int index = 0;

                @Override
                public boolean hasNext() {
                    return index < nodeList.getLength();
                }

                @Override
                public IIOMetadataNode next() {
                    if (!hasNext())
                        throw new NoSuchElementException();
                    return (IIOMetadataNode) nodeList.item(index++);
                }
            };
    }