Don't know if anybody still having problems launching jar files, but I was able to create an app that uses the Terminal command "java -jar file.jar" to launch a jar and made a simple app that permits the user to again launch with only a double click. One just needs to right click jar->get info->set Dot-Jar as default for all, and the rest is history. The app "may" have some since I can't test every scenario, but should work. I only been able to test it on my Mac OS X Mountain Lion, but I believe it should work for Lion also. For more info if you're interested, contact me to get the Dot-Jar(BETA) app, send me an email to [email protected]
Btw, I'm an computer engineer student and I made this app to help others and it free.
And it's completely related to this post since he is asking for the script which I used to make this simple app. If nobody finds this useful then sorry for that...