You can get start with the next one:

make sure your Java application is using JDK 8 binary to run Java programs compiled on Java 8. If your application is using JAVA_HOME environment variable to locate Java then make sure you set it correctly to point JDK 8 installation

export JAVA_HOME=/usr/lib/jvm/java-8-oracle

Make sure JAVA_HOME is pointing to correct JDK 8 installation directory.

Also,add JAVA_HOME on PATH as shown below:

export PATH = $PATH:$JAVA_HOME;