I think it is a common practice to initiate resumable uploads on the server side, and hand the session URL to clients.
However, it seems that java-storage does not expose any methods to get the session URL for a resumable upload.

Describe alternatives you've considered
One can use Signed URL with single-request upload. However, for large files, resumable upload is preferable.

https://cloud.google.com/storage/docs/access-control/signed-urls#signing-resumable