The Prefuse toolkit haven't been updated since 2009 and the last build is from 2007. Is there any other Java visualization packages as powerful as Prefuse but has active community support/development?
Protovis is the successor of Prefuse (and now, D3 is under active development). Protovis-Java is a partial implementation of the Protovis toolkit in Java. There's a nice example gallery, but I have no experience with the Java side.
As an alternative, you might consider Processing, with some example of use in Java here, or its Javascript counterpart, Processing.js. There were even a port for Scala + Processing: Spde.