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How To manually Install Oracle Java 12 on Debian 9



Java and the JVM (Java's virtual machine) are required for many kinds of software, including Tomcat, Jetty, Glassfish, Cassandra, Jenkins, Gradle, ELK Stack, Graylog and  Eclipse IDE
Java Development Kit (JDK) is a package of tools for developing Java-based software, whereas the JRE is a package of tools for running Java code.The JRE can be used as a standalone component to simply run Java programs, but it's also part of the JDK. The JDK requires a JRE because running Java programs is part of developing them.

This post is designed to guide you through the manually installation process, of the Java Developer Kit (JDK) using binary formats. While this post will focus on  version 12.0.1  You can still select the version you wish to use for your projects and still be able to use the procedure's detailed here as long as the version that you chose is in binary format. When you finish, you'll be able to use the JDK to develop software or use the Java Runtime to run software.

Prerequisites

A non-root user with sudo access

Installing the JDK

I will use the command line to download the JDK,  but if you have access to browser you can use that for simplicity.

If your installing form the command line, use the following command

wget --no-check-certificate --no-cookies --header "Cookie: oraclelicense=accept-securebackup-cookie" https://download.oracle.com/otn-pub/java/jdk/12.0.1+12/69cfe15208a647278a19ef0990eea691/jdk-12.0.1_linux-x64_bin.tar.gz

Extract the downloaded JDK archive to the desired directory e.g /usr/

tar -zxvf jdk-12.0.1_linux-x64_bin.tar.gz

sudo mv jdk-12.0.1 /usr/

Install Oracle Java

Once you have moved java to the location you want, then you must run update-alternatives commands to install the Java on your system.

 sudo update-alternatives --install /usr/bin/java java /usr/jdk-12.0.1/bin/java 1
  update-alternatives: using /usr/jdk-12.0.1/bin/java to provide /usr/bin/java (java) in auto mode


Verify Java Installation

We have successfully installed Oracle Java on our Debian system. Let’s use the following command to verify the installed version of Java on our system.

java -version
java version "12.0.1" 2019-04-16
Java(TM) SE Runtime Environment (build 12.0.1+12)
Java HotSpot(TM) 64-Bit Server VM (build 12.0.1+12, mixed mode, sharing)

javac -version
-bash: javac: command not found

Setup Environmental Variable

 Many programs written using Java use JAVA_HOME, JRE_HOME, etc. environmental variables So, we need to set the environmental variables like below.

export PATH=$PATH:/usr/jdk-12.0.1/bin
export JAVA_HOME=/usr/jdk-12.0.1
export J2SDKDIR=/usr/jdk-12.0.1

javac -version
javac 12.0.1
Note:
Multiple JDK versions can coexist in a system and we can change the default version as per our requirements at any time.

sudo update-alternatives --config java

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