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Web Browser Java Plugin Issues

We've had problems on Athena with Java plugins in the past. A Java plugin is necessary for applets that require more advanced Java features than are supported by the base Java level incorporated in the browser. We have seen situations where the browser will sometimes recognize the plugin but not at other times, for no evident reason. For a plugin to be active, it should appear in the Firefox listing of plugins, and the enabled column on the right should say Yes for all features). We've also seen some applets that work with certain plugin versions but break with other ones.

Generally, a Java plugin is provided via the default Java version installed in the Athena release. You can see what Java version(s) this supports by typing about:plugins in the URL entry dialog in Firefox. It's possible to change the Java plugin used by Firefox, but the details are somewhat tricky; see discussion below:

A major change in how the Java plugin is implemented took place as of Firefox 3.6. The rest of this document applies only to Firefox 3.6 and later.

Setting correct tags for embedded applets that need to run in multiple browsers is tricky; see this page for advice, and also here.

You can only use the Java plugin from Java releases 1.6.0_10 or later. The plugin is located in the following directory:

/afs/athena.mit.edu/software/<Java version locker>/distrib/${ATHENA_SYS}/jre/lib/${ATHENA_SYS}

and is named libnpj2.so. The MOZ_PLUGIN_PATH environment variable can no longer be used to select the plugin. Instead, you must put a copy of it or a link to it in your ~/.mozilla/plugins directory within your home directory. The preferred way to do this, which will find the most current plugin on either 32 bit or 64 bit systems, is to make this link as follows:

libnpjp2.so -> /afs/athena.mit.edu/software/java/current/distrib/@sys/jre/lib/@sys/libnpjp2.so

This path will ensure that you are always using the most recent plugin version available. If you want to be sure that you are only using this plugin and no others, you may need to find and delete or rename all other copies of libnpjp2.so on your machine. You will generally need to sudo or be root to do this. You can use an older plugin if you replace the path in the libnpjp2.so link by one that is explicitly version-dependent (replace java/current by a version locker such as java_v1.6.0_38).

To enable the Firefox Java plugin, select Tools -> Add-ons -> Plugins -> Java Plug-in and make sure this feature is set to enabled (you may not see the plugin listed until you make the link described above and restart Firefox).

As of this writing, the default version of the plugin accessed through the "current" path above is in the java_v1.7.0_21 locker.

Oracle and Mozilla have articles supplying more information.

Java Web Start issues

It is possible that the javaws version in recent debathena releases will fail to launch applets in Firefox. To get around this, you can use the javaws version in the Athena java locker. To do this, select Edit -> Preferences -> Applications -> Java Web Start Document, select Use other... and enter /afs/athena.mit.edu/software/java/current/bin/javaws.

Users still having problems with our configurations can send questions or comments to the 3partysw@mit.edu mailing list.