GWT "database" to store data server-side

I'm looking for the easiest way to store data on the server-side of the GWT app. The application is typical: consists of th开发者_开发技巧e 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.

Thanks for any hints, Rafal

One option is the AppEngine DataStore. You can use it through the JDO and JPA APIs. If you want a simpler API for the AppEngine DataStore, try Objectify.