ClassNotFoundException running applets when updating to Java7 jre

One day I got this message that said ”do you want to update java to the latest version”, which I then accepted. However, after the update everything ”java” running in Internet Explorer and Firefox stopped working. The testpages (JavaTest 1,
JavaTest 2) did not work, all they said was ”JavaVersionDisplayApplet.class ClassNotFoundException” and ”testjava2_1.testvmapplet.class ClassNotFoundException”.

I then tried to uninstall and reinstall everything Java on my Windows 7 64-bit machine. Tried both the 32 and 64 bit Java version, tried both the jdk and the jre. Nothing worked! After a couple of hours I found this thread that lead me in the right direction.

Solution
1) Go to the ”windows control panel” and press the Java icon. Alternatively, go to your jre folder and execute ”javacpl.exe”. If you have multiple jre’s installed then only change one of them because I think they overwrite eachothers settings.

2) Go to the Java-tab and change ”settings for java runtime environment”. Add ”-Djava.net.preferIPv4Stack=true” to the run paramaters for your jre. When you are done with this step it should work again. Restart your browser and test your java.

It should look like this (in swedish)
jre-control-panel

3) If you are still having problem, check the ”network settings” in the java control panel.

4) A good way to ”debug” java jre trouble like this is to enable the java console. This can be done in the ”advanced” tab of the java control panel. By enabling the console you get a window which shows valuable debug information.

I think this problem is somehow related to our network at work which is IPv6 enabled. Or perhaps it is our VPN that uses IPv6. Well, I have given this problem to much attention. Back to work…

3 reaktioner till “ClassNotFoundException running applets when updating to Java7 jre”

  1. This is life-saving article….I must thank you for this. This is my problem since 3-4 months long….

    I’ve tried a lot of suggestion to make my Java running such as: disabling firewall, remove older java, installing 32 bit and 64 bit java, tried almost all types of browser, etc…but no one seems working.

    But by simply adding the parameter, my Java working instantly!

    Again, thank you

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