Major Description
The com.opensymphony.xwork2.inject.ContainerImpl class uses a ThreadLocal that contains an InternalContext array. Because of this, the InternalContext class (and everything it references transitively) cannot be garbage collected. A very similar issue is described in further detail here: http://www.szegedi.org/articles/memleak.html
I'm submitting a patch which simply changes the type of the array from InternalContext to Object. This appears to fix the issue.