The chapter on integration with Spring and JPA/Hibernate is, in my opinion, deep enough for people who know those technologies, but not deep enough for someone who is not familiar with those technologies. The Spring integration is basically out of the box, but we walk you through how to declare some spring beans and how to let spring do autowiring and/or manage the creation of your framework components, such as actions and interceptors. We then show how to manage Spring's JPA/Hibernate support to quickly integrate JPA/Hibernate, using annotations, into our sample application.
As for Ajax, we have a great example of how to use Custom results that will return JSON or XML responses to your Ajax clients. You will be quite excited to see that struts 2 actions are so clean that you can re-use the same action for Ajax or classic web aplication request servicing. Just switch the result type, i.e. the language that the action speaks, with some configuration changes.