Transmission, MIME-types, Java?

I'm posting this here for two reasons, a) the solution works but sounds like overkill and b) because I couldn't find any information on the interschnitzel directly -- it just happened to be a solution for another application that worked in this case too.

After updating Transmission (my favourite bittorrent client) on my Ubuntu 8.04 desktop machine, I found that torrent files I downloaded weren't appearing in my client, but they weren't appearing on my desktop either.

Sometimes they worked if I downloaded the .torrent file more than once, but more often than not, they didn't.

Looking through all the usual suspects (MIME-types in Nautilus, etc) proved unsatisfying, so I had a look in my .xsession-errors file (using: tail -f ~/.xsession-errors from a terminal while downloading a file, and found:

GCJ PLUGIN: thread 0x816c470: NP_GetMIMEDescription
GCJ PLUGIN: thread 0x816c470: NP_GetMIMEDescription return
GCJ PLUGIN: thread 0x816c470: NP_GetValue
GCJ PLUGIN: thread 0x816c470: NP_GetValue: returning plugin name.
GCJ PLUGIN: thread 0x816c470: NP_GetValue return
GCJ PLUGIN: thread 0x816c470: NP_GetValue
GCJ PLUGIN: thread 0x816c470: NP_GetValue: returning plugin description.
GCJ PLUGIN: thread 0x816c470: NP_GetValue return

GCJ?

Ah, the Open Java Variation of Sun's Java Runtime.

Turns out, if you have the Ubuntu Multiverse and Universe repositories configured & you install the ubuntu-restricted-extras package (the one that gives you multimedia encoding and playback capabilities, Java, Flashplayer amongst other things) it installs the Open Java (openjdk-6-jre) variations and not the Sun one.

To install the Sun Java Runtime from Multiverse, run the following from a terminal window:

sudo apt-get install sun-java6-bin

Then, to make Ubuntu use it, instead of the OpenJDK code, type:

sudo update-java-alternatives -s java-6-sun

Then restart Transmission & your chosen Web Browser and try downloading your .torrent files again.