You can clone with
HTTPS or Subversion.
Both the zip and tarball download links for the 2.0.4 release tag return "Not found" instead of the expected file.
Somehow I managed to set the tag for JDOM-2.0.4 to be the same as JDOM 1.1.1 ... this is why those links don't work properly. I will fix that.
For the moment, you realize that those links are "source code" links and not the actual product download? For the full (compiled) JDOM project go to http://jdom.org/downloads/index.html
Regardless, I will clean up the tag, and as a result, the source tarball/zip should work. This will take me a little time because I am also going to sort out the repository in terms of branching in preparation for JDOM 2.1.x
In the interim, you can just pull the code from github....
Tag JDOM-2.0.4 now point to a valid location (the correct location), and work
I'm fully aware those are "source code" links since that's what I want and was trying to package for Gentoo. :)