On upgrading to xenial, the package tzdata-java was removed and is indeed no longer available. I managed to install older JDK versions (still needed for some development) from the openjdk-r PPA, but tzdata-java isn't in there either. I have seen some unit tests fail because the timezone data isn't available.
Why was tzdata-java removed, and more importantly, how can I install some kind of reasonably up-to-date timezone information for Java?