The book covers backend connectivity in great detail. Chapter 3 is an overview of the techniques you can use for connecting to a backend server. Chapters 6-10 are example applications, each dealing with a different type of backend. The application in chapter 6 looks a a serverless application that saves it's state as a browser cookie or using Google Gears offline storage. The application in chapter 7 connects to four different third party servers using JSONP as the method of communication. The application in chapter 8 connects to the Blogger web service which uses GData and Google's AuthSub. In chapter 9, the application connects to a Java servlet
using GWT RPC implementation. Chapter 10 looks at connecting to backends with an action based approach to connect to backends that may have been used with HTML forms previously, a REST approach for connecting to a stateless backend, and a typical Java approach using GWT RPC, a Servlet, and Hibernate.
I talk about how by using GWT you can shift your application away from a stateful server implementation towards a stateless server. GWT lets you put more application state in the client instead of on the server. Instead of making many round trips to the server for each action, as you would with a JSP based approach, you can manipulate the model through many actions in the client and commit the changes to the server in batches. Tis is a fundamental architectural difference between GWT and JSP which means that you will rely much less on session variables.
Of course you may still need session variables. The application in chapter 9 uses session variables to hold the currently logged in user's identity. But you will probably think less about translating session variables to GWT than you will about creating a programmatic interface for your GWT application to talk to your backend (using GWT RPC, XML, or JSON). Your GWT application is effectively decoupled from your server implementaton so any session variables will have to be sent over this type of interface.
[ November 13, 2007: Message edited by: Ryan Dewsbury ]