How can I use JNLP to download Java 7?

I'm developing a rich Internet application that requires a Java 7 platform. How can its associated JNLP file ensure the installation of that platform?

I've tried several variations on the following in the JNLP file (mostly playing with the URL in the "href" attribute):

<jnlp ...>
  ...
  <resources>
    <java version="1.7+" href="http://download.java.net/jdk7/m5"/>
    ...
  </resources>
</jnlp>

but nothing seems to work -- I always wind up being sent her开发者_Go百科e, where there is no Java 7 release.

As far as a quick google search says, Java 7 has not offically been "released" yet -- you can get the latest early access snapshots, but it seems September 2010 or later is the release date.

Java Web Start is not open sourced with the JDK (alas), so this is still implementation dependent and we cannot refer to the official Oracle Java source to indicate how this should be done.

There are developer builds of Java 7 out in the wild now. You can start experimenting with it to at least get this right for when it is officially released.