Question

After using the ImagesService to transform an uploaded image, I would like to store it back into a new Blob file and make it available through getServingUrl() as provided by the ImagesService.

Storing the image in a new AppEngineFile as described here works fine and I am able to open and view it locally using the dev server.

However when passing the blobKey for the new AppEngineFile to ImagesService.getServingUrl() a

java.lang.IllegalArgumentException: Could not read blob.

exception is thrown. Any ideas what the problem could be? This is the code I use to transform and store an uploaded image (blobKey and blobInfo correspond to the uploaded file, not the newly created one).

/* Transform image in existing Blob file */
Image originalImage = ImagesServiceFactory.makeImageFromBlob(blobKey);
Transform verticalFlip = ImagesServiceFactory.makeVerticalFlip();
ImagesService imagesService = ImagesServiceFactory.getImagesService();
Image newImage = imagesService.applyTransform(verticalFlip, originalImage);

/* Store newImage in an AppEngineFile */
FileService fileService = FileServiceFactory.getFileService();
AppEngineFile file = fileService.createNewBlobFile(blobInfo.getContentType());
FileWriteChannel writeChannel = fileService.openWriteChannel(file, true);
ByteBuffer buffer = ByteBuffer.wrap(newImage.getImageData());
writeChannel.write(buffer);

/* closeFinally assigns BlobKey to new file object */
writeChannel.closeFinally();
BlobKey newBlobKey = fileService.getBlobKey(file);

Edit:

The above code is correct, the problem was storing a String representation of the new blob key using newBlobKey.toString() instead of newBlobKey.getKeyString().

Answer 1

The following works fine when executed at the end of the code posted in the question:

String url = imagesService.getServingUrl(newBlobKey)

The URL can then be used to scale and crop the new image as described in the docs
http://code.google.com/appengine/docs/java/images/overview.html#Transforming_Images_from_the_Blobstore