Java 1.4.2 Plug-in on Fedora Core 4
Lately I've been using several Linux distributions to test a Java Applet used in Documentum's Unified Client Facilities (UCF). I've tested Red Hat Enterprise 3 and Fedora Core 4 using Firefox 1.0.7 and the Java plug-in (1.4.2_09 and 1.5_05). In my testing, the Applet failed to load on Fedora Core 4 using JRE 1.4.2; however, JRE 1.5 on Fedora Core 4 worked fine.
The Applet is embedded in an HTML page using the standard "code" tag. The browser HTML engine encounters the tag and informs the Java plug-in that it has some work to do. The Java plug-in then attempts to download and execute the code archive referenced in the tag. The 1.4.2 plug-in was reporting an inability to download the Applet archive from the web server. I verified that the URL of the Applet archive (JAR file) was accessible through the browser. It was, so there was no reason that the Java plug-in should report an error while trying to download the archive. I was puzzled.
I googled the problem a bit and learned that it stems from the IPv6 support in the Java 1.4.2 plug-in. The JRE tries to create an IPv6 socket to the system hosting the JAR file, but screws up somewhere along the line and reports that the connection failed. It looks like the Java 1.5 plug-in might need to be the minimum requirement for browser-based Linux clients.
Here are some of the links I found documenting the bug in JRE 1.4.2:
JRoller posting
Sun Bug Entry