Strictly speaking, is this a Java exploit? I might be reading this wrong, but it seems to me the server needs to be previously compromised so that a file is deployed. Only then is tomcat/other told to install a web portal to give easy access to the server for miscreants.
I'm guessing the ease of installing WARs is what's being used as an easy way of giving access, but apart from that, it's hardly a Java exploit?
I could certainly be wrong, not many details in that article.