I decided to put together a simple web app on my way to learning Java and Spring. Tirtle allows users to track daily numbers such as how many calories they eat in a day. The project uses the Spring Web MVC framework and is running on Google App Engine.
The most frustrating part of the project was just getting everything configured and getting a working server up and running. I feel there is a lack of documentation aimed at beginners, although part of my problems may have been related to jumping right in with Spring + GAE. I chose Spring Framework version 3.0 (the latest version), but there seemed to be more documentation and blog tutorials available for version 2.5. I found an official Web MVC tutorial on the Spring Source site, but it only covered version 2.5.
I had several problems figuring out the base configuration settings, and getting all the correct .jar files in my classpath. webmvc.jar was especially mysterious, because it is not included in the Spring Framework distribution. I ended up finding it via a Google search, but I have yet to find the official download from Spring Source.
Once I got a basic server running, the available documentation for how to actually use Spring seemed pretty good. The Web MVC framework works similar to every other MVC framework you have used. Classes are annotated to turn them into controllers, and controller methods are annotated to turn them into request handlers. You can use either JSPs (Java Server Pages: Java embedded in HTML similar to PHP) or a templating system for your view layer.
The Web MVC stuff is all built on top of Spring's dependency injection framework, so the simple MVC annotations you use are actually shortcuts to lots of complicated XML configuration. Spring's standard DI tools can be used to inject other non-mvc dependencies into your controllers. I used the DI features to configure a simple authentication object (didn't have time to figure out how to get Spring Security working) and also an ORM interface to Google's DataStore (objectify-appengine with the help of objectify-appengine-spring).