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.

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?
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

ozarov ozarov · Accepted Answer · 2015-11-04T03:38:36

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.

Server side upload to Blobstore - Java Google Appengine

1 Answers