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Although Java seems to be past its height, there are still loads of applications out there that need Java. And unfortunately lots of them won't work with the open alternatives. To make the installation of Java possible in Debian (Wheezy or newer) the program make-jpkg is provided in the package java-package.
Somehow though, there seems to be a bug in installing the browser plugin in the correct path, after installing the created .deb package the plugin won't work. The correct alternative will be set (i.e. linking /etc/alternatives/iceweasel-javaplugin.so to /usr/lib/jvm/j2re1.7-oracle/lib/amd64/libnpjp2.so), but this link is used in /usr/lib/iceweasel/plugins instead of /usr/lib/mozilla/plugins. To fix this situation and make the Java plugin work again there are two different approaches.
Personally I prefer this method. The disadvantage is that you'll need to repeat this every time Java gets an update. Simply create the symbolic link in the correct place (as 'root'):
# ln -s /etc/alternatives/iceweasel-javaplugin.so /usr/lib/mozilla/plugins
The disadvantage of this method is that you need to do it for every user, and that you'll have to remember to undo this once there is another alternative. Create the necessary plugin directory in your home directory (as user):
% mkdir -p ~/.mozilla/plugins
Create the symbolic link to the Java plugin:
% ln -s /etc/alternatives/iceweasel-javaplugin.so ~/.mozilla/plugins