GWT“数据库”存储数据服务器端

I'm looking for the easiest way to store data on the server-side of the GWT app. The application is typical: consists of the client-side interface and server-side that performs all the calculations. I just need to store the data on the server. The application would be deployed to google code so the solution must obey the app engine limitations.I'm looking for the easiest way to store data o