Getting a blobKey after writing byte-array to Google Cloud Storage

Question

I'm writing a byte-array from an image to Google Cloud Storage, how do I prevent accidentally overwriting some other file in GCS and how do I retreive the blobKey after I've written this byte-array to GCS?

GcsFilename fileName = new GcsFilename("my-bucket-name", "someFileName.jpg");
GcsOutputChannel outputChannel = GcsServiceFactory.createGcsService().createOrReplace(fileName, GcsFileOptions.getDefaultInstance());
outputChannel.write(ByteBuffer.wrap(bytearray));
outputChannel.close();