Scribe is an OAuth library for Java, written by the asker himself. 😉
Note: I post this here as an answer so that other googlers have a choice of alternatives.
For another library-based alternative, see my other answer “Jersey OAuth signature library”.
Some code to illustrate usage:
OAuthService service = new ServiceBuilder()
.provider(TwitterApi.class)
.apiKey("your_api_key")
.apiSecret("your_api_secret")
.build();
...
Token requestToken = service.getRequestToken();
String your_token = requestToken.getToken();
...
Verifier verifier = new Verifier("your_previously_retrieved_verifier");
Token accessToken = service.getAccessToken(requestToken, verifier);
Creating the request:
OAuthRequest request = OAuthRequest(Verb.GET, "http://api.twitter.com/1/direct_messages.json");
service.signRequest(accessToken, request);
Response response = request.send();