As many others did, I also upgraded OS X to Yosmite, losing java 6. Because we are using some software still depending on java 6, I have no other choice than to install java 6 on my Mac Pro. First thing I did, was downloading a version that seems to work fine on my Mac: http://support.apple.com/kb/DL1572

Just install as usual. When you're done, you'll need to do some terminal-work too:
sudo mkdir -p /Library/Internet\ Plug-Ins/disabled

sudo mv /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin /Library/Internet\ Plug-Ins/disabled/

sudo ln -sf /System/Library/Java/Support/Deploy.bundle/Contents/Resources/JavaPlugin2_NPAPI.plugin/ /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin

That's it, you can test your version on: http://www.java.com/nl/download/installed8.jsp?detect=jre