Hello,
Just to share, got the same problem after upgrading two from my xwiki from 7.x to 8..1
Since 24/05/2016 with xwiki 8.1 java runtime Java is 8 (before 7).
To solve it fast :
vi /etc/apt/sources.list
Just add :
deb http:~/~/ftp.fr.debian.org/debian/ <http://ftp.fr.debian.org/debian/>
jessie-backports main
Then
sudo apt-get update
apt-get install openjdk-8-jre-headless
apt-get install openjdk-8-jdk
Then if Java7 was installed previously, change main 'java’ and 'javac’ command to
point to Java8
sudo /usr/sbin/update-java-alternatives -s java-1.8.0-openjdk-amd64
Then everything works fine for me.
Regards,
zoldax