Why is the REST API of Android able to connect to a GAE web application directly?

I 开发者_开发知识库have been trying to find a way to implement a RESTful web service and then consume this service from an Android REST client. The reason is that Android intrinsically only supports consuming a RESTful web service.

However, when I came across this web site, I got totally confused! The author is using the org.apache.http.client API to connect to a web application built by Google App Engine. I tested it and it worked!

But, to my understanding, isn't Google App Engine a RPC-styled web service? Doesn't it need external libraries such as Restlet to convert to a RESTful web service? Why is the REST API of Android able to connect to a GAE web application directly?

Could someone explain this to me?

Google App Engine is just an web app server. As long as a framework only uses classes in GAE's JRE White List then it should be usable on the server. This includes Spring mVC, Jersey, Restlet and other tools on this list. For one of my Android apps I use a GAE server to run RESTful Web Services with Spring MVC and it works great.