Java8_Ubuntu14

The PPA has the instructions, more detail at Redmine #7905.

Basically:

sudo apt-get install software-properties-common
sudo add-apt-repository ppa:openjdk-r/ppa
sudo apt-get update
sudo apt-get install openjdk-8-jdk
sudo update-alternatives --config java
sudo update-alternatives --config javac
sudo update-alternatives --config keytool

Tomcat 7

1. Edit /etc/init.d/tomcat7:

find_openjdks()
{
        for jvmdir in /usr/lib/jvm/java-8-openjdk-*
        do
                if [ -d "${jvmdir}" -a "${jvmdir}" != "/usr/lib/jvm/java-8-openjdk-common" ]
                then
                        OPENJDKS=$jvmdir
                fi
        done
        for jvmdir in /usr/lib/jvm/java-7-openjdk-*
        do
                if [ -d "${jvmdir}" -a "${jvmdir}" != "/usr/lib/jvm/java-7-openjdk-common" ]
                then
                        OPENJDKS="${OPENJDKS} ${jvmdir}" 
                fi
        done
        for jvmdir in /usr/lib/jvm/java-6-openjdk-*
        do
                if [ -d "${jvmdir}" -a "${jvmdir}" != "/usr/lib/jvm/java-6-openjdk-common" ]
                then
                        OPENJDKS="${OPENJDKS} ${jvmdir}" 
                fi
        done
}

2. Make Apache jk module use openjdk-1.8, in /etc/libapache2-mod-jk/workers.properties or /etc/apache/workers.properties file:

   workers.java_home=/usr/lib/jvm/java-8-openjdk-amd64

3. Restart Apache2

4. Restart Tomcat7