Get a Google Cloud Storage file from its BlobKey

Question

I wrote a Google App Engine application that makes use of Blobstore to save programmatically-generated data. To do so, I used the Files API, which unfortunately has been deprecated in favor to Google Cloud Storage. So I'm rewriting my helper class to work with GCS.

I'd like to keep the interface as similar as possible as it was before, also because I persist BlobKeys in the Datastore to keep references to the files (and changing the model of a production application is always painful). When i save something to GCS, i retrieve a BlobKey with

BlobKey blobKey = blobstoreService.createGsBlobKey("/gs/" + fileName.getBucketName() + "/" + fileName.getObjectName());

as prescribed here, and I persist it in the Datastore.

So here's the question: the documentation tells me how to serve a GCS file with blobstoreService.serve(blobKey, resp); in a servlet response, BUT how can I retrieve the file content (as InputStream, byte array or whatever) to use it in my code for further processing? In my current implementation I do that with a FileReadChannel reading from an AppEngineFile (both deprecated).

Answer 1

Here is the code to open a Google Storage Object as Input Stream. Unfortunately, you have to use bucket name and object name and not the blob key

GcsFilename gcs_filename = new GcsFilename(bucket_name, object_name);
GcsService service = GcsServiceFactory.createGcsService();
ReadableByteChannel rbc = service.openReadChannel(gcs_filename, 0);
InputStream stream = Channels.newInputStream(rbc);