A much-anticipated feature was successfully implemented this week - bundled JRE. Gradle now automatically bundles any given JRE with the generated application package.
To test this feature, you'll need any JRE 8 distribution with JavaFX in it. Grab a package from these vendors:
Extract the downloaded files and use
gradlew clean build -PbundleJre=/path/to/jre to generate the ZIP packages inside ./build/distributions. Try them in any system, it'll execute the bundled JRE only.
The generated launcher packages now include the JRE. After executing the startup script, you can have a look at the generated log files to get more information about the bundled JRE.
Be sure to check out this post on my weekly GSoC forum thread.