I used XStream many years ago, but I see that the libraries is not updated since 2008 (latest news). Is there now a more modern and up to dates Java XML serialization libra
The fact that something hasn't been updated for 3 years doesn't mean that it is out of date. It might simply mean that there has been no need to update it. If there is no need to change a project, why change it?
Another explanation for the apparent lack of "progress" is that changing library APIs tends to be disruptive to projects that depend on them. This is particularly problematic for projects that combine lots of third-party components and libraries into one Java application.
Looking for alternatives to a library is a good thing, but simply doing this because the library hasn't been updated recently is not. If XStream does what you need, stick with it. Newer doesn't necessarily mean better.
UPDATE - 2019
XStream has been receiving updates with a new release at least once a year since 2011. Refer to the Changes page for details, and look at the activity on the Github repository for the project. As of now, the theory that XStream is not being maintained is (IMO) thoroughly debunked.