在GAE BlobStore中旋转图像

Question

I'm trying to rotate an image that is in the blobstore and then save it back to the blobstore, but I can't figure out how to save it back to the blobstore? I did find this , but it looks like the FileService API is deprecated, so what do I use instead? Here's my code so far:

// Get image from blobstore
Image img = ImagesServiceFactory.makeImageFromBlob(new BlobKey(document.blobstoreKey));

// Rotate 90 degrees
Transform transform = ImagesServiceFactory.makeRotate(90);
img = ImagesServiceFactory.getImagesService().applyTransform(transform, img);

// HERE: How to save back to the blobstore?
...

Answer 1

Unfortunately, you're running into one the limitations of blobstore as documented at https://cloud.google.com/appengine/docs/java/blobstore/ ...:

An application cannot create or modify Blobstore values except through files uploaded by the user.

...and that's exactly what you want to do -- create a blobstore value, not by having the user upload a file, but rather by saving the byte[] returned by img.getImageData() .

If you're in control of the client (Javascript app on the browser) you could hack some trick around this, sending the bytes down to the browser and having Javascript immediately turn around and "upload" the new blobstore. But this is really hacky -- and inherently slow, adding a "round trip" to the browser and back for potentially large-ish image data.

Rather, in your shoes, I'd take this as one more inducement to leave blobstore behind and move instead to google cloud storage -- specifically https://cloud.google.com/appengine/docs/java/googlecloudstorageclient/ .

With GCS, you could for example just use the service's createOrReplace method, documented at https://cloud.google.com/appengine/docs/java/googlecloudstorageclient/javadoc/ , passing it a ByteBuffer.wrap of that byte[] , and voila, it's all done for you, simply, rapidly, without complications.