Google-tasks is a project mainly written in Java, it's free.
Trying google Tasks API and OAuth 2
= Google Tasks =
Playing with Google Tasks API, at the moment I've implemented OAuth 2.
To configure the application, copy src/main/webapp/WEB-INF/app-config-template.xml to src/main/webapp/WEB-INF/app-config.xml and customize Google API Client Id, Google API Secret and callback URL within the application pointing to
/auth-response.Build with maven from command line or using m2eclipse plugin.
OAuth2 example program http://code.google.com/p/google-api-java-client/wiki/OAuth2Draft10