A Java Webstart application cannot be launch if there's no network connection even when "offline-allowed" is true.

The Java Webstart Launcher will thrown a FailedDownloadException:
com.sun.deploy.net.FailedDownloadException: Unable to load resource: http://<some domain and dir>/SwingHelloWorld3.jnlp
 at com.sun.deploy.net.DownloadEngine.actionDownload(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getCacheEntry(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getCacheEntry(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getResourceCacheEntry(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getResourceCacheEntry(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getResource(Unknown Source)
 at com.sun.deploy.net.DownloadEngine.getResource(Unknown Source)
 at com.sun.javaws.Launcher.updateFinalLaunchDesc(Unknown Source)
 at com.sun.javaws.Launcher.prepareToLaunch(Unknown Source)
 at com.sun.javaws.Launcher.launch(Unknown Source)
 at com.sun.javaws.Main.launchApp(Unknown Source)
 at com.sun.javaws.Main.continueInSecureThread(Unknown Source)
 at com.sun.javaws.Main$1.run(Unknown Source)
 at java.lang.Thread.run(Unknown Source)