How To Install and manage Java JDK on Oracle Linux

taken from :
http://lorenzkeller.blogspot.ae/2015/01/how-to-install-and-manage-java-jdk-on.html

Every Time I set up an Oracle Linux server, I ask myself, how have I done it last time ...

1. Check which Java Version (JDK7, JDK8, ...) is certified with your software.
e.g. Oracle Fusion Middleware supported system configurations:
http://www.oracle.com/technology/software/products/ias/files/fusion_certification.html 

2. Check support policy, esp. end of life for your desired Java Version
http://www.oracle.com/technetwork/java/javase/downloads/eol-135779.html

3. Download JDK
http://www.oracle.com/technetwork/java/javase/downloads/index.html

4. Install JDK 

# ls -l jdk*
-rw-r--r--. 1 oracle oinstall 126679286 Jan  9 13:01 jdk-7u71-linux-x64.rpm
-rw-r--r--. 1 oracle oinstall 142191827 Jan  9 13:06 jdk-8u25-linux-x64.rpm

# rpm -Uhv jdk-7u71-linux-x64.rpm
Preparing...                ########################################### [100%]
   1:jdk                    ########################################### [100%]
Unpacking JAR files...
    rt.jar...
    jsse.jar...
    charsets.jar...
    tools.jar...
    localedata.jar...
    jfxrt.jar...

5. Check Java Version

# java -version
java version "1.7.0_71"
Java(TM) SE Runtime Environment (build 1.7.0_71-b14)
Java HotSpot(TM) 64-Bit Server VM (build 24.71-b01, mixed mode)

If this is your expected Java Version - fine! Your are done!
If you still have a pointer to an older version, move on ...

...

6. A non expected Java Version is present?     lets say, JDK8 is still present, but you need to move back to JDK7

# java -version
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

7. Check Java install locations

# ls -l /usr/java/
total 8
lrwxrwxrwx. 1 root root   16 Jan  9 13:24 default -> /usr/java/latest
drwxr-xr-x. 8 root root 4096 Jan  9 13:49 jdk1.7.0_71
drwxr-xr-x. 9 root root 4096 Jan  9 13:40 jdk1.8.0_25
lrwxrwxrwx. 1 root root   21 Jan  9 13:40 latest -> /usr/java/jdk1.8.0_25

8. Make use of alternatives system to switch between versions

8.1 Syntax of alternatives

# /usr/sbin/alternatives
alternatives version 1.3.49.3 - Copyright (C) 2001 Red Hat, Inc.
This may be freely redistributed under the terms of the GNU Public License.

usage: alternatives --install 
                    [--initscript ]
                    [--slave ]*
       alternatives --remove 
       alternatives --auto 
       alternatives --config 
       alternatives --display 
       alternatives --set 

common options: --verbose --test --help --usage --version
                --altdir --admindir 

8.2 Register your JDKs for alternatives

usage: alternatives --install 

# /usr/sbin/alternatives --install /usr/bin/java java /usr/java/jdk1.7.0_71/bin/java 17071

(where priority represents 17071 for jdk1.7.0_71)

# /usr/sbin/alternatives --install /usr/bin/java java /usr/java/jdk1.8.0_25/bin/java 18025

(where priority represents 18025 for jdk1.8.0_25)

8.3 Now to switch between the versions

8.3.1 Check current java version, again

# java -version
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

8.3.2 Change the current java version

 # /usr/sbin/alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
   1           /usr/java/jdk1.7.0_71/bin/java
*+ 2           /usr/java/jdk1.8.0_25/bin/java

Enter to keep the current selection[+], or type selection number: 1

8.3.3 Check your current java version has changed 

# java -version
java version "1.7.0_71"
Java(TM) SE Runtime Environment (build 1.7.0_71-b14)
Java HotSpot(TM) 64-Bit Server VM (build 24.71-b01, mixed mode)

9. Keep your path JDK dynamic

The idea is, when you install for example WebLogic Server, to use a dynamic location to your JDK.
I do this with a symbolic link.
I have a folder /opt/oracle/java where I create a symbolic link, that points to the jdk.
As normal user I create the symbolic link:

$ ln -s /usr/java/jdk1.8.0_25 /opt/oracle/java/java

When an updated jdk version in available, after install I only change the symbolic link:

$ rm /opt/oracle/java/java
$ ln -s /usr/java/jdk1.8.0_31 /opt/oracle/java/java

For the WebLogic Server, the path to java will remain. No reconfiguration is needed.
So I only have to restart the WebLogic Server to use the latest JDK.