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javajarjava-web-startjnlp

Web Start JAR downloads being blocked

I have an app that is deployed using Java Web Start. On certain client machines, as Web Start downloads the JAR files (about 60 of them), the downloads sporadically hang, and the app fails to launch.

To determine whether the problem was with Web Start directly or with the client network settings, we wrote a separate script to download the JARs in sequence using wget. The script also suffers from the same issue, eventually hanging after a few JARs have been successfully downloaded. Introducing a slight pause in between downloads allows the downloads to succeed.

So, the problem is not with Web Start directly, but unfortunately we're between a rock and a hard place. We have to use Web Start in the short term, and doing custom troubleshooting of client networks/firewalls is not ideal (it's happening on several networks).

I have two questions:

  • What typically blocks the download of a sequence of JAR files?
  • Is there a way to make Web Start download the JARs with slight pauses in between, as a way to work around the client network problems?

I would appreciate any tips from anyone who has encountered similar issues.

Solution

  • Common issues with downloading/launching Java Webstart apps:

    • Antivirus/firewall prevents download, either completely or typically freezing when the progress bar is nearing the end. Especially common with AVG and McAfee. Fix: whitelist javaws.exe + javaw.exe, turn off file transfer inspection. Some users have reported having to uninstall the antivirus completely before the issue would go away.
    • Wrong proxy settings: http://www.java.com/en/download/help/proxy_setup.xml (use direct connection if you don't need proxy)
    • Error message "Splash: recv failed": Often caused by Comodo firewall. Fix: you must add javaws.exe to trusted applications in Comodo firewall, see http://geekdrop.com/content/java-web-start-splash-recv-failed-fix . Could also be caused by wrong proxy settings, see above.
    • "MalformedURLException: unknown protocol: socket", bad proxy, see above.