How do I run a jar when I double-click it?
You can prepend a short script to the .jar to make it executable via double click. In Terminal do the following:

$ cat &gt; header-template &lt;&lt;"EOF"
#!/bin/sh

exec java -jar $0 "$@" &gt; /dev/null

EOF
$ cat header-template "System FRONT.jar" &gt; executable_app
$ chmod +x executable_app


Double-clicking executable_app should now launch the application.



Why does this work in the first place? Well, a .jar is just a .zip archive which gets unpacked and executed by java. And the zip format allows to prepend additional stuff in front of the actual archive. Any zip unarchiver skips this part until it finds the start of the archive (indicated by PK...).