Red hat linux jre

Build your first application using Java on RHEL 7 with OpenJDK 8

Get started developing with Java 8 on Red Hat Enterprise Linux in under 10 minutes.

Introduction and Prerequisites

In this tutorial, you will see how to get started with Java development on Red Hat Enterprise Linux by creating a simple Hello World application. You will install a Java Development Kit (JDK), and learn what Java packages are available. The whole tutorial should take less than 10 minutes to complete.

You will need a Red Hat Enterprise Linux 7 system with a current Red Hat subscription that allows you to download software and updates from Red Hat. If you don’t have a Red Hat Enterprise Linux subscription, get Red Hat Enterprise Linux Developer Suite after registering at developers.redhat.com.

If you encounter difficulties at any point, see Troubleshooting and FAQ.

1. Prepare your system

In this step, you will learn how to use the yum package management tool to find out which Java packages are available and to download and install updates for your system. You will also see how to enable access to additional software repositories for a wider selection of packages.

First, start a Terminal window from the Application menu. Then use su — to change to the root user ID, and use subscription-manager to verify that you have access to Red Hat Software Repositories.

$ su - # subscription-manager repos --list-enabled

If you don’t see any enabled repositories, your system might not be registered with Red Hat or might not have a valid subscription. See Troubleshooting and FAQ for more information.

Download and install updates

Now download and install any available updates by running yum update . If updates are available, yum will list them and ask if it is OK to proceed.

Determine if any Java packages are already installed

Your system may have one or more Java Runtime Environments (JRE) installed. You can see the list of installed packages with yum list installed . You can narrow the list to show only package names starting with java.

The output includes the package name, version information, and the software repository it was installed from.

If you have a JRE installed, you can skip the following steps. When you install a JDK, a JRE will also be installed.

To tell if java is in your PATH use which :

If java is in your path, determine which version:

View available JDKs

You can view or search packages that are available to be installed with yum list available :

# yum list available java\*devel

The output will show the package name and the software repository it resides in. Only software repositories that have been enabled for downloading are included in the results.

Enabling additional software repositories

There are a number of additional software repositories for Red Hat Enterprise Linux. These aren’t enabled by default as the packages in them have support policies that differ from the main Red Hat Enterprise Linux packages. Some of these repositories have packages that are of interest to Java developers:

• The Optional RPMs repository includes a number of Java development tools and libraries. Most Java developers will want to enable this repository.
• Versions of the JRE and JDK from IBM can be found in the Supplementary RPMs repository.
• The Oracle JRE and JDK are located in the Third-party Oracle Java RPMs repository.

Instructions are provided below for the command-line. If your system has a graphical desktop installed, you can use the graphical version of subscription-manager . Red Hat Subscription Manager can be started from the System Tools group of the Applications menu. Alternatively, you can start it from the command prompt by typing subscription-manager-gui . Select Repositories from the System menu of subscription manager.

Note: The naming of Red Hat software repositories is specific to the server, workstation, or desktop editions of Red Hat Enterprise Linux your system is using. The examples below are for server installations. If you are using the workstation or desktop edition, substitute -workstation- or -desktop- for -server- in the following commands.

To see what repositories are currently enabled:

# subscription-manager repos —list-enabled

You can also get a list of the available repositories that aren’t enabled:

# subscription-manager repos —list-disabled

Enable the optional RPMs repository:

# subscription-manager repos —enable rhel-7-server-optional-rpms

After you enable a repository, it will be searched along with the other enabled repositories when you issue a yum command.

2. Setup your development environment

In this next step, you will a JDK. You should still have the previous Terminal window open, and still be running under su .

First, view the list of available JDKs to install:

# yum install available java\*devel

The naming convention for JDK packages is java-version—provider-devel_ . Version 1.8.0 of the OpenJDK is named java-1.8.0-openjdk-devel . The JRE components are packed separately. The JRE package name is the same as the JDK without -devel . When you install the JDK package, it will automatically install the corresponding JRE.

Install the JDK, changing the version number if necessary, with the following command:

# yum install java-1.8.0-openjdk-devel

Check that javac is now in your path and check which version:

Managing Java versions

It is possible to have multiple versions of the JRE and JDK packages installed concurrently. You might have a set of applications or services installed your system that requires more than one versions of Java. JRE and JDK packages for Red Hat Enterprise Linux are installed in separate directories under /usr/lib/jvm . This allows them to be installed concurrently. However, only one version can be in the shell’s command path as java or javac at a time.

Note: A Java application or service that is packaged as an RPM following best practices will specify the necessary JRE version as a package dependency. This will cause yum to find and install the specific JRE that is needed. The application or service will use the specific JRE’s full path instead of relying on the shell’s command search path.

It is possible to choose which version gets used when you type java or javac by using the system’s alternatives command or by using environment variables to change the path. The alternatives command will make changes that apply to the whole system. For a development system, this is a reasonable choice. For a shared system, like a server running multiple applications, changing alternatives could have undesired side effects.

To set the default JDK using alternatives :

# alternatives —config javac

To set the default JRE using alternatives :

Note that a number of related Java commands will be changed at the same time. For a full list use alternatives —display :

# alternatives --display javac # alternatives --display java

Using environment variables it is possible to set PATH and JAVA_HOME for the current session, for a specific user, system-wide, or for a specific application.

Setting JAVA_HOME

For tools that need the JAVA_HOME environment variable, set it to /usr/lib/jvm/java-version . For example, to specify the OpenJDK 1.8.0 JDK, use JAVA_HOME=/usr/lib/java-1.8.0-openjdk in your scripts and/or build configuration. There are several permutations under /usr/lib/jvm that include the full name of the JRE or JDK down to the specific patch number, or progressively more general references such as java-1.8.0-openjdk , ‘java-1.8.0`, or just java .

3. Hello World and your first application

In this step, you will create and compile a simple Java application using the command line. If you don’t have a Terminal window open, start it from the Applications menu. You should run under your normal user ID, If you are still running as root, type exit .

First, you need to create Hello.java using your preferred text editor such as vi , nano , or gedit :

Add the following text to the file:

If it compiled without error, run it:

`$ java Hello Hello, Red Hat Developers World from Java 1.8.0_71

Where to go next?

• Dive into Java enterprise application development with Ticket Monster, a moderately complex application that demonstrates how to build modern applications using JBoss web technologies.
• Go to the Red Hat Developers site, to learn more about Enterprise Java and JBoss technologies.

Troubleshooting and FAQ

1. As a developer, how can I get a Red Hat Enterprise Linux subscription? If you don’t have a Red Hat Enterprise Linux subscription, register at developers.redhat.com and then download Red Hat Enterprise Linux Developer Suite.
2. Where can I find Java development tools as libraries such as ant and maven for Red Hat Enterprise Linux? I can’t find many Java packages for Red Hat Enterprise Linux, where should I look? Many Java development tools and libraries are located in the Optional RPMs repository. The Optional RPMs repository isn’t enabled by default as the packages in them have support policies that differ from the main Red Hat Enterprise Linux packages. Step 1 of this tutorial shows how to enable the Optional RPMs repository, which is recommended for Java developers. The following command will enable the repository: # subscription-manager repos —enable rhel-7-server-optional-rpms Now you can install ant , maven , and other Java development tools: # yum install ant maven
3. Is a Java Interactive Development Environment (IDE) such as Eclipse available for Red Hat Enterprise Linux? JBoss Developer Studio is built on Eclipse, it provides superior support for your entire development lifecycle. It includes features that will help you quickly get started developing Java applications. For development purposes, $0 subscriptions are available after registering at developers.redhat.com For more information see JBoss Developer Studio Overview.
4. How do I find out what JRE and JDKs are already installed? You can see the list of installed packages with yum list installed . You can narrow the list to show only package names starting with java. The naming convention for JDK packages is java-version—provider-devel_ . Version 1.8.0 of the OpenJDK is named java-1.8.0-openjdk-devel . The JRE components are packed separately. The JRE package name is the same as the JDK without -devel . # yum list installed java\* The output includes the package name, version information, and the software repository it was installed from. If you want to install the matching JDK for a JRE that is already installed, add -devel to the package name. For example, if you have the java-1.8.0-openjdk JRE, you can add the JDK components with the following command: # yum install java-1.8.0-openjdk-devel
5. Why is an OpenJDK JRE already installed on my system? Several Red Hat packages require a JRE. The most common is the Internet browser package, which installs Firefox and OpenJDK to be able to run Java applets.
6. Are JRE/JDKs other than OpenJDK available for Red Hat Enterprise Linux? Can I install Oracle’s JRE/JDK on Red Hat Enterprise Linux? OpenJDK, IBM, and Oracle JRE/JDKs are available from Red Hat software repositories for easy installation through yum . The IBM and Oracle packages are in optional repositories which aren’t enabled by default. Enable the supplementary RPMS repository for the IBM packages, or the Third-party Oracle Java RPMs repository for the Oracles packages. If you have a graphical desktop installed, Red Hat Subscription Manager can be started from the System Tools group of the Applications menu. Select Repositories from subscription manager’s System menu. To enable additional repositories from the command line, run one, or both of the following commands after changing to the root user ID with su — :

# subscription-manager repos --enable rhel-7-server-supplementary-rpms

# subscription-manager repos --enable rhel-7-server-thirdparty-oracle-java-rpms

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