Facebook connect  and rest of API
see it here http://restfb.com/ and it works on the GAE

client side http://code.google.com/p/facebook4gwt/

and http://code.google.com/p/gwt-facebook/

and some sampe

Facebook Java api example to publish on Wall

http://blog.theunical.com/facebook-integration/facebook-java-api-example-to-publish-on-wall/