Recently Google announced its support for OpenID, called "Federated Login", to let any site enable their users to sign on by their Google accounts, without registrations.
This is really a good news, and for Java developers they can write some code to make the 3rd-part site to connect to Google. There are already lots of libaries that can be used in J2EE. However, after I do some evaluation of these libaries, I do not find a suitable libary. The well-known "OpenID4Java", is too large (46MB!), with dependencies on many other libaries. So I decided to write a small, but very lightweight libary to support OpenID 2.0 spec, called "JOpenID".
It is very small, with only 48KB including both source & binary. You can download from http://code.google.com/p/jopenid/downloads/list.
Sample code is also provided:
http://code.google.com/p/jopenid/source/browse/trunk/JOpenId/src/com/javaeedev/openid/Main.java
http://code.google.com/p/jopenid/source/browse/trunk/JOpenId/src/com/javaeedev/openid/Main.java
It has been fully tested based on Google accounts. However, I think it also can support Yahoo! OpenID, but with little information provided by Yahoo! I do not test yet.