CODEWITHSUNDEEP
javaapplet
pkalinow
pkalinow

Reputation: 1741

Java applet fails to reload on Internet Explorer

I have an applet that has a logout"button. The button ends the session by calling a CGI script and then kills Java VM by calling System.exit(). The problem is when a user tries to log in again in the same browser window - the applet fails to load with ClassNotFoundException:

load: class lucent/fm/parts/BlankPage.class not found.
java.lang.ClassNotFoundException: lucent.fm.parts.BlankPage.class
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: open HTTP connection failed:http://example.com/html/lucent/fm/parts/BlankPage/class.class
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more
Exception: java.lang.ClassNotFoundException: lucent.fm.parts.BlankPage.class

It appears only on Internet Explorer, not in Firefox. Java Plugin is:
Java Plug-in 1.6.0_20
Using JRE version 1.6.0_20-b02 Java HotSpot(TM) Client VM

The direct scenario is the following:
1. Log in to the system (load the applet).
2. Log out (it closes the applet, but the browser window persists).
3. Click on the address bar and press Enter.
4. The applet fails to load and the ClassNotFoundException can be seen in Java Console.
5. Refresh the page - the server redirects to the login page; after logging in, the applet again does not load and throws the exception.

Looking at the Apache access log proved that in the step 4 that the browser (or plugin) tries to load jar files and gets a HTTP error. It is OK because the session has expired. The strange thing happens in the 5th point - there is no request for jars! It seems that the browser or plugin remembers failed attempts and does not even try to load jar files. It only tries to load a raw .class file, which is not present on the server.

Is my conclusion correct? How can I deal with such an error? Is it possible to force Java plugin to load jar files?

I checked that enabling caching in Java Control Panel does not help. Setting the codebase_lookup parameter to "false" is not helpful, too. It only prevents from trying to load the "class" file directly.

Thanks in advance for any suggestions.

Upvotes: 3

Views: 4026

Answers (2)

Andrew Thompson
Andrew Thompson

Reputation: 168825

I have an applet that has a "logout" button. The button ends the session by calling a CGI script and then kills Java VM by calling System.exit().

An applet calling System.exit(anyNumber) is crudely equivalent to a guest burning down the house of their host. Applets (even trusted applets) should never try to end the VM. The VM will be ended by the browser when all applets in a page that share the VM have finished their destroy() methods and a subsequent period of time as chosen by the browser.

BTW - I recall one version of Mozilla/FF where calling System.exit(int) not just ended the VM, but also crashed the browser!

Upvotes: 2

Michał Šrajer
Michał Šrajer

Reputation: 31182

If your html with applets is not static (cgi, php, etc), then after logging out, you can try to force different URL pointing to the jar file (i.e. instead of "my.jar" use "my.jar?random=1235232").

Also, you can try to play with cache HTTP headers.

Another potential workaround will be to reconfigure apache to serve the jars always - even when session has been closed (if that's acceptable).

Upvotes: 1

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