Server side upload to Blobstore - Java Google Appengine

Question

I create data in the server (gae) and I want to store it in Blobstore. I saw many answers on how to do this giving a BlobStore URL to the client, but there is no client or HTTP request: it's just an asynchronous task.

1. Then I guess I should use createUploadUrl(), and instead of giving this URL to a client, from my code HTTP Post my data to it via URL Fetch. This looks weird, isn't there another API for this?

2. Let's say that the files I want in Blobstore are already stored in my GCS default bucket. Can I just tell Blobstore about them using the gcs location "/gs/bucketname/file"? I tried this by

GcsFilename filename = new GcsFilename(bucketName, fileId);
String gcsKey = "/gs/" + bucketName + "/" + filename.getObjectName();
BlobKey blobKey = blobstoreService.createGsBlobKey(gcsKey);
GcsOutputChannel outputChannel = gcsService.createOrReplace(filename, GcsFileOptions.getDefaultInstance());
ObjectOutputStream oout = new ObjectOutputStream(Channels.newOutputStream(outputChannel));
oout.writeObject(myDataObjectToPersist);
oout.close();

// ...at some other point I have checked the file is correctly stored in
// GCS and I can fetch it using /gs/bucket/fileId
// but it doesn't seem to be in Blobstore, so when
InputStream stream = new BlobstoreInputStream(new BlobKey(blobKey.keyString))
// ... this gives a BlobstoreInputStream$BlobstoreIOException: BlobstoreInputStream received an invalid blob key...

Is this something conceptually wrong - like if I use GcsOutputChannel to save it I will not get it from Blobstore even if I create a BlobKey, or is it something that could work but I just did something wrong?

1K thanks

Answer 1

Why would you want to store the file in blobstore as opposed to writing and reading it directly from GCS?

Yes, you can create a BlobKey for a file stored in GCS, and can use the key in some of the blobstore API (such as fetchData and serve ) but unfortunately not in all. Some of the blobstore API (such as BlobstoreInputStream ) depends on BlobInfo and that is not created when using the GCS client.