How to install Jdk in centos

How to Install JDK (Java Development Kit) on CentOS

A comprehensive guide to installing and configuring the Java Development Kit (JDK) on CentOS, covering both OpenJDK and Oracle JDK installations.

The Java Development Kit (JDK) is an essential component for developing and running Java applications. This article provides a step-by-step guide on how to install JDK on CentOS, covering both the open-source OpenJDK and the proprietary Oracle JDK. We'll also cover how to set up environment variables and manage multiple Java versions.

Understanding JDK Options: OpenJDK vs. Oracle JDK

Before proceeding with the installation, it's important to understand the differences between OpenJDK and Oracle JDK. OpenJDK is a free and open-source implementation of the Java Platform, Standard Edition (Java SE). Oracle JDK is the official, commercial build of Java SE from Oracle. While they are largely similar, Oracle JDK may include some proprietary features or optimizations. For most development and production environments, OpenJDK is a perfectly suitable and often preferred choice due to its open-source nature and licensing.

flowchart TD
    A[Start] --> B{Choose JDK Type?}
    B -->|OpenJDK| C[Install OpenJDK]
    B -->|Oracle JDK| D[Install Oracle JDK]
    C --> E[Set Default Java Version]
    D --> E
    E --> F[Verify Installation]
    F --> G[End]

JDK Installation Workflow on CentOS

Method 1: Installing OpenJDK on CentOS

OpenJDK is readily available in the CentOS repositories, making it the easiest and recommended way to install JDK. This method ensures that your Java installation is managed by the system's package manager, simplifying updates and maintenance.

1. Step 1: Update System Packages

Always start by updating your system's package list to ensure you get the latest available packages and dependencies.

2. Step 2: Search for Available OpenJDK Versions

Use yum to search for available OpenJDK packages. This will show you the different versions you can install.

3. Step 3: Install OpenJDK

Choose the desired OpenJDK version (e.g., Java 11 or Java 8) and install it. For Java 11, use the following command:

4. Step 4: Verify Installation

After installation, verify that Java has been installed correctly and check its version.

sudo yum update -y
yum search openjdk
sudo yum install java-11-openjdk-devel -y
java -version

Commands to install and verify OpenJDK 11

Method 2: Installing Oracle JDK on CentOS

Installing Oracle JDK requires downloading the binary from the Oracle website and manually configuring it. This method is suitable if you specifically need Oracle's proprietary features or have licensing requirements. Remember that Oracle JDK's licensing has changed, and commercial use may require a subscription.

1. Step 1: Download Oracle JDK

Visit the official Oracle Java download page (oracle.com/java/technologies/downloads) and download the appropriate .rpm package for CentOS. You will likely need an Oracle account to download.

2. Step 2: Install the RPM Package

Navigate to the directory where you downloaded the .rpm file and install it using yum.

3. Step 3: Verify Installation

Check the installed Java version to confirm a successful installation.

cd ~/Downloads
sudo yum localinstall jdk-*-linux-x64.rpm
java -version

Commands to install Oracle JDK from an RPM package

Managing Multiple Java Versions with alternatives

CentOS uses the alternatives system to manage different versions of the same command. This is particularly useful if you have multiple JDKs installed and need to switch between them.

1. Step 1: List Available Java Alternatives

See all installed Java versions that the alternatives system is aware of.

2. Step 2: Set Default Java Version

Use the alternatives --config java command to interactively select your preferred default Java version. You will be prompted to enter a selection number.

3. Step 3: Verify the Change

Confirm that the default Java version has been updated.

sudo alternatives --config java
java -version

Commands to manage Java versions using alternatives

Setting JAVA_HOME Environment Variable

Many Java applications and build tools (like Maven or Gradle) rely on the JAVA_HOME environment variable to locate the JDK installation. It's good practice to set this variable.

1. Step 1: Find Your JDK Installation Path

The path depends on whether you installed OpenJDK or Oracle JDK. For OpenJDK, it's usually under /usr/lib/jvm/.

2. Step 2: Edit the Environment Profile

Open the /etc/profile file (for system-wide setting) or ~/.bashrc (for user-specific setting) with a text editor.

3. Step 3: Add JAVA_HOME and PATH

Add the following lines to the end of the file, replacing /path/to/your/jdk with your actual JDK installation path.

4. Step 4: Apply Changes

Source the profile file to apply the changes immediately without rebooting.

5. Step 5: Verify JAVA_HOME

Check if the JAVA_HOME variable is correctly set.

readlink -f /usr/bin/java

sudo vi /etc/profile

# Add these lines:
export JAVA_HOME="/usr/lib/jvm/java-11-openjdk-11.0.12.0.7-0.el8_4.x86_64"
export PATH=$JAVA_HOME/bin:$PATH

source /etc/profile
echo $JAVA_HOME

Setting the JAVA_HOME environment variable for OpenJDK 11