title: Java - find tzdata version in use regardless of JRE version
body: <p>We have a simple utility app that reads all the time zone data used in a JRE and displays it all in a simple table. We need to use an older version of the JRE (6_24) for an upcoming product release (due to other issues apparently), but we also need to include newer time zone updates in that release (that would otherwise be included in, say, 6_29). We're already packaging a private JRE that will be installed, so getting the time zone updates into that private JRE using the <a href="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html" rel="noreferrer">TZUpdater tool</a> is not the issue - The issue is reading/verifying which version of the <a href="http://www.oracle.com/technetwork/java/javase/tzdata-versions-138805.html" rel="noreferrer">tzdata</a> (e.g. tzdata2010o, tzdata2011k) is being read with the utility app (i.e. which version is being used in the JRE the app is running in). The app currently displays the <em>JRE version</em> in the title bar, but with the time zone updates, that's no longer sufficient to determine which <em>time zone data</em> version is in use.</p>
  
  <p>I've looked into the <a href="http://download.oracle.com/javase/6/docs/api/java/util/TimeZone.html" rel="noreferrer">TimeZone</a> class, but it doesn't seem to provide this information - perhaps there is a system property that holds this info? The TZUpdater tool knows which version is being used, so it must be available somewhere - I can't imagine they would analytically determine which version is in use in the update tool... Anybody know where to locate this info?</p>