Error while starting jenkins

Today, when I install and setup Jenkins, I am getting the following error while starting the jenkins service.

OS : CentOS release 6.8 (Final)

Following is the error:

Running from: /usr/lib/jenkins/jenkins.war
May 21, 2017 7:38:37 PM Main deleteWinstoneTempContents
WARNING: Failed to delete the temporary Winstone file /tmp/winstone/jenkins.war
Jenkins requires Java7 or later, but you are running 1.7.0_131-mockbuild_2017_02_13_15_19-b00 from /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.131.x86_64/jre
java.lang.UnsupportedClassVersionError: winstone/Launcher : Unsupported major.minor version 52.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:803)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:442)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:64)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:354)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:348)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:347)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
        at Main._main(Main.java:224)
        at Main.main(Main.java:112)

Solution to fix the issue:

1. Take the backup of /etc/init.d/jenkins to a safe location.
2.  update-alternatives --config java (to the latest java) 
3. Update the file /etc/init.d/jenkins after candidates with your result of echo $JAVA_HOME

The  /etc/init.d/jenkins snippet is below
# Search usable Java as /usr/bin/java might not point to minimal version required by Jenkins.
# see http://www.nabble.com/guinea-pigs-wanted-----Hudson-RPM-for-RedHat-Linux-td25673707.html
candidates="
/usr/java/latest/bin/java
/etc/alternatives/java
/usr/lib/jvm/java-1.8.0/bin/java
/usr/lib/jvm/jre-1.8.0/bin/java
/usr/lib/jvm/java-1.7.0/bin/java
/usr/lib/jvm/jre-1.7.0/bin/java
/usr/bin/java


4. Restart jenkins

Patching 0 for a variable in python

As part of a program logic, i need to patch 0 for a variable to make sure the total length of the string is 3.

Here the variable name is shivin

shivin = shivin.zfill(3)
return shivin