When changing environments for certain applications, Java being a key one which has many different files and variables to be configured you want to be able to gt the full environment changed in one go, rather than having to set different paths, etc.
The RHEL alternatives command does just that, allowing you to change your Java environment so that java, javac, javadoc all get set to the correct location without having to change your PATH and other environment variables.
Here's how you can set Java to the Oracle version after you have installed it on to your RHEL system. You'll note that if you use the alternatives command you will get the JRE rather than the JDK, and if you're developing or require the JDK you will want to change the settings.
Before we can add a new option, we need to find out the next available number to use;
sudo alternatives --config java
There are 3 programs which provide 'java'.
Selection Command
-----------------------------------------------
1 java-1.7.0-openjdk.x86_64 (/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.141-2.6.10.1.el7_3.x86_64/jre/bin/java)
+ 2 java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.el7_3.x86_64/jre/bin/java)
3 /usr/java/jdk1.8.0_131/jre/bin/java
Enter to keep the current selection[+], or type selection number:
From the above output we can see that our next available slot is 4, so we need to add Oracle JDK to this location;
sudo alternatives --install /usr/bin/java java /usr/java/jdk1.8.0_131/bin/java 4
The above command will also identify the javac and javadoc commands too, so no other changes are required.
Now we can set Oracle Java as our default JDK;
sudo alternatives --config java
There are 4 programs which provide 'java'.
Selection Command
-----------------------------------------------
1 java-1.7.0-openjdk.x86_64 (/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.141-2.6.10.1.el7_3.x86_64/jre/bin/java)
+ 2 java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.el7_3.x86_64/jre/bin/java)
3 /usr/java/jdk1.8.0_131/jre/bin/java
4 /usr/java/jdk1.8.0_131/bin/java
Enter to keep the current selection[+], or type selection number:
Select 4 and you will have Oracle JDK default system wide.
