Groovy's XML capabilities are powerful enough that you may not need to consider other alternatives such as XQuery. If you wish to use XQuery though, it isn't hard to do. Here we just added mxquery.jar from the MXQuery project to our CLASSPATH. MXQuery is still under development and may not support all of XQuery yet but it appears to be making good progress and has a relatively small footprint.
Once our path is set up, we can run the following script:
Depending on your XQuery processor and operating system, you might be able to make use of XQuery directly from the command line instead of calling it from Java or Groovy.