Yes, you can do this by submitting a cURL request to the github API that is documented here: https://developer.github.com/v3/.
EX:
curl -G https://api.github.com/repos/{repo-owner}/{repo-name}
(where in your case repo-name and owner are both radiant)
This will return a JSON object with a bunch of links to fetch whatever information you want associated with the repo.
I know offhand that there is a short description field in the response, as well as a bunch of *_url fields that contain urls to fetch other pieces of information associated with the repo like contents_url, comments_url, git_tags_url, and many more.
To access these you would just send a similar get request to the one above to the url stored in the field.
If you need information on how to make cURL requests in java, there's a a good SO post on it already here.