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Using jlink to customize Java runtime environment

Red Hat build of OpenJDK 21

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Abstract

Red Hat build of OpenJDK 21 is a Red Hat offering on the Red Hat Enterprise Linux platform. The Using jlink to customize Java runtime images guide provides an overview of Jlink, and explains how to create a customized Java runtime image by using jlink.

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Procedure

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Making open source more inclusive
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Red Hat is committed to replacing problematic language in our code, documentation, and web properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases. For more details, see our CTO Chris Wright’s message.

You can create a custom Java runtime environment from a non-modular application by using the jlink tool.

Prerequisites

Procedure

  1. Create a simple Hello World application by using the Logger class.

    1. Check the base Red Hat build of OpenJDK 21 binary exists in the jdk-17 folder: 

      $ ls jdk-17
bin  conf  demo  include  jmods  legal  lib  man  NEWS  release
$ ./jdk-17/bin/java -version
openjdk version "17.0.10" 2021-01-19 LTS
OpenJDK Runtime Environment 18.9 (build 17.0.10+9-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 17.0.10+9-LTS, mixed mode)
      Copy to Clipboard Toggle word wrap

    2. Create a directory for your application: 

      $ mkdir -p hello-example/sample
      Copy to Clipboard Toggle word wrap

    3. Create hello-example/sample/HelloWorld.java file with the following content: 

      package sample;

import java.util.logging.Logger;

public class HelloWorld {
    private static final Logger LOG = Logger.getLogger(HelloWorld.class.getName());
    public static void main(String[] args) {
        LOG.info("Hello World!");
    }
}
      Copy to Clipboard Toggle word wrap

    4. Compile your application: 

      $ ./jdk-17/bin/javac -d . $(find hello-example -name \*.java)
      Copy to Clipboard Toggle word wrap

    5. Run your application without a custom JRE: 

      $ ./jdk-17/bin/java sample.HelloWorld
Mar 09, 2021 10:48:59 AM sample.HelloWorld main
INFO: Hello World!
      Copy to Clipboard Toggle word wrap

      The previous example shows the base Red Hat build of OpenJDK requiring 311 MB to run a single class.

    6. (Optional) You can inspect the Red Hat build of OpenJDK and see many non-required modules for your application: 

      $ du -sh jdk-17/
313M	jdk-17/
      Copy to Clipboard Toggle word wrap 
      $ ./jdk-17/bin/java --list-modules
java.base@17.0.1
java.compiler@17.0.1
java.datatransfer@17.0.1
java.desktop@17.0.1
java.instrument@17.0.1
java.logging@17.0.1
java.management@17.0.1
java.management.rmi@17.0.1
java.naming@17.0.1
java.net.http@17.0.1
java.prefs@17.0.1
java.rmi@17.0.1
java.scripting@17.0.1
java.se@17.0.1
java.security.jgss@17.0.1
java.security.sasl@17.0.1
java.smartcardio@17.0.1
java.sql@17.0.1
java.sql.rowset@17.0.1
java.transaction.xa@17.0.1
java.xml@17.0.1
java.xml.crypto@17.0.1
jdk.accessibility@17.0.1
jdk.attach@17.0.1
jdk.charsets@17.0.1
jdk.compiler@17.0.1
jdk.crypto.cryptoki@17.0.1
jdk.crypto.ec@17.0.1
jdk.dynalink@17.0.1
jdk.editpad@17.0.1
jdk.hotspot.agent@17.0.1
jdk.httpserver@17.0.1
jdk.incubator.foreign@17.0.1
jdk.incubator.vector@17.0.1
jdk.internal.ed@17.0.1
jdk.internal.jvmstat@17.0.1
jdk.internal.le@17.0.1
jdk.internal.opt@17.0.1
jdk.internal.vm.ci@17.0.1
jdk.internal.vm.compiler@17.0.1
jdk.internal.vm.compiler.management@17.0.1
jdk.jartool@17.0.1
jdk.javadoc@17.0.1
jdk.jcmd@17.0.1
jdk.jconsole@17.0.1
jdk.jdeps@17.0.1
jdk.jdi@17.0.1
jdk.jdwp.agent@17.0.1
jdk.jfr@17.0.1
jdk.jlink@17.0.1
jdk.jpackage@17.0.1
jdk.jshell@17.0.1
jdk.jsobject@17.0.1
jdk.jstatd@17.0.1
jdk.localedata@17.0.1
jdk.management@17.0.1
jdk.management.agent@17.0.1
jdk.management.jfr@17.0.1
jdk.naming.dns@17.0.1
jdk.naming.rmi@17.0.1
jdk.net@17.0.1
jdk.nio.mapmode@17.0.1
jdk.random@17.0.1
jdk.sctp@17.0.1
jdk.security.auth@17.0.1
jdk.security.jgss@17.0.1
jdk.unsupported@17.0.1
jdk.unsupported.desktop@17.0.1
jdk.xml.dom@17.0.1
jdk.zipfs@17.0.1
      Copy to Clipboard Toggle word wrap

      This sample Hello World application has very few dependencies. You can use jlink to create custom runtime images for your application. With these images you can run your application with only the required Red Hat build of OpenJDK dependencies.

  2. Determine module dependencies of your application using jdeps command: 

    $ ./jdk-17/bin/jdeps -s ./sample/HelloWorld.class
HelloWorld.class -> java.base
HelloWorld.class -> java.logging
    Copy to Clipboard Toggle word wrap

  3. Build a custom java runtime image for your application: 

    $ ./jdk-17/bin/jlink --add-modules java.base,java.logging --output custom-runtime
$ du -sh custom-runtime
50M	custom-runtime/
$ ./custom-runtime/bin/java --list-modules
java.base@17.0.10
java.logging@17.0.10
    Copy to Clipboard Toggle word wrap
    Note

    Red Hat build of OpenJDK reduces the size of your custom Java runtime image from a 313 M runtime image to a 50 M runtime image.

  4. You can verify the reduced runtime of your application: 

    $ ./custom-runtime/bin/java sample.HelloWorld
Jan 14, 2021 12:13:26 PM HelloWorld main
INFO: Hello World!
    Copy to Clipboard Toggle word wrap

    The generated JRE with your sample application does not have any other dependencies.

    You can distribute your application together with your custom runtime for deployment.

    Note

    You must rebuild the custom Java runtime images for your application with every security update of your base Red Hat build of OpenJDK.

You can create a custom Java runtime environment from a modular application by using the jlink tool.

Prerequisites

Procedure

  1. Create a simple Hello World application by using the Logger class.

    1. Check the base Red Hat build of OpenJDK 21 binary exists in the jdk-17 folder: 

      $ ls jdk-17
bin  conf  demo  include  jmods  legal  lib  man  NEWS  release
$ ./jdk-17/bin/java -version
openjdk version "17.0.10" 2021-01-19 LTS
OpenJDK Runtime Environment 18.9 (build 17.0.10+9-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 17.0.10+9-LTS, mixed mode)
      Copy to Clipboard Toggle word wrap

    2. Create a directory for your application: 

      $ mkdir -p hello-example/sample
      Copy to Clipboard Toggle word wrap

    3. Create hello-example/sample/HelloWorld.java file with the following content: 

      package sample;

import java.util.logging.Logger;

public class HelloWorld {
    private static final Logger LOG = Logger.getLogger(HelloWorld.class.getName());
    public static void main(String[] args) {
        LOG.info("Hello World!");
    }
}
      Copy to Clipboard Toggle word wrap

    4. Create a file called hello-example/module-info.java and include the following code in the file: 

      module sample
{
    requires java.logging;
}
      Copy to Clipboard Toggle word wrap

    5. Compile your application: 

      $ ./jdk-17/bin/javac -d example $(find hello-example -name \*.java)
      Copy to Clipboard Toggle word wrap

    6. Run your application without a custom JRE: 

      $ ./jdk-17/bin/java -cp example sample.HelloWorld
Mar 09, 2021 10:48:59 AM sample.HelloWorld main
INFO: Hello World!
      Copy to Clipboard Toggle word wrap

      The previous example shows the base Red Hat build of OpenJDK requiring 311 MB to run a single class.

    7. (Optional) You can inspect the Red Hat build of OpenJDK and see many non-required modules for your application: 

      $ du -sh jdk-17/
313M	jdk-17/
      Copy to Clipboard Toggle word wrap 
      $ ./jdk-17/bin/java --list-modules
java.base@17.0.1
java.compiler@17.0.1
java.datatransfer@17.0.1
java.desktop@17.0.1
java.instrument@17.0.1
java.logging@17.0.1
java.management@17.0.1
java.management.rmi@17.0.1
java.naming@17.0.1
java.net.http@17.0.1
java.prefs@17.0.1
java.rmi@17.0.1
java.scripting@17.0.1
java.se@17.0.1
java.security.jgss@17.0.1
java.security.sasl@17.0.1
java.smartcardio@17.0.1
java.sql@17.0.1
java.sql.rowset@17.0.1
java.transaction.xa@17.0.1
java.xml@17.0.1
java.xml.crypto@17.0.1
jdk.accessibility@17.0.1
jdk.attach@17.0.1
jdk.charsets@17.0.1
jdk.compiler@17.0.1
jdk.crypto.cryptoki@17.0.1
jdk.crypto.ec@17.0.1
jdk.dynalink@17.0.1
jdk.editpad@17.0.1
jdk.hotspot.agent@17.0.1
jdk.httpserver@17.0.1
jdk.incubator.foreign@17.0.1
jdk.incubator.vector@17.0.1
jdk.internal.ed@17.0.1
jdk.internal.jvmstat@17.0.1
jdk.internal.le@17.0.1
jdk.internal.opt@17.0.1
jdk.internal.vm.ci@17.0.1
jdk.internal.vm.compiler@17.0.1
jdk.internal.vm.compiler.management@17.0.1
jdk.jartool@17.0.1
jdk.javadoc@17.0.1
jdk.jcmd@17.0.1
jdk.jconsole@17.0.1
jdk.jdeps@17.0.1
jdk.jdi@17.0.1
jdk.jdwp.agent@17.0.1
jdk.jfr@17.0.1
jdk.jlink@17.0.1
jdk.jpackage@17.0.1
jdk.jshell@17.0.1
jdk.jsobject@17.0.1
jdk.jstatd@17.0.1
jdk.localedata@17.0.1
jdk.management@17.0.1
jdk.management.agent@17.0.1
jdk.management.jfr@17.0.1
jdk.naming.dns@17.0.1
jdk.naming.rmi@17.0.1
jdk.net@17.0.1
jdk.nio.mapmode@17.0.1
jdk.random@17.0.1
jdk.sctp@17.0.1
jdk.security.auth@17.0.1
jdk.security.jgss@17.0.1
jdk.unsupported@17.0.1
jdk.unsupported.desktop@17.0.1
jdk.xml.dom@17.0.1
jdk.zipfs@17.0.1
      Copy to Clipboard Toggle word wrap

      This sample Hello World application has very few dependencies. You can use jlink to create custom runtime images for your application. With these images you can run your application with only the required Red Hat build of OpenJDK dependencies.

  2. Create your application module: 

    $ mkdir sample-module
$ ./jdk-17/bin/jmod create --class-path example/ --main-class sample.HelloWorld --module-version 1.0.0 -p example sample-module/hello.jmod
    Copy to Clipboard Toggle word wrap

  3. Create a custom JRE with the required modules and a custom application launcher for your application: 

    $ ./jdk-17/bin/jlink --launcher hello=sample/sample.HelloWorld --module-path sample-module --add-modules sample --output custom-runtime
    Copy to Clipboard Toggle word wrap

  4. List the modules of the produced custom JRE.

    Observe that only a fraction of the original Red Hat build of OpenJDK remains. 

    $ du -sh custom-runtime
50M	custom-runtime/
$ ./custom-runtime/bin/java --list-modules
java.base@17.0.10
java.logging@17.0.10
sample@1.0.0
    Copy to Clipboard Toggle word wrap
    Note

    Red Hat build of OpenJDK reduces the size of your custom Java runtime image from a 313 M runtime image to a 50 M runtime image.

  5. Launch the application using the hello launcher: 

    $ ./custom-runtime/bin/hello
Jan 14, 2021 12:13:26 PM HelloWorld main
INFO: Hello World!
    Copy to Clipboard Toggle word wrap

    The generated JRE with your sample application does not have any other dependencies besides java.base, java.logging, and sample module.

    You can distribute your application that is bundled with the custom runtime in custom-runtime. This custom runtime includes your application.

    Note

    You must rebuild the custom Java runtime images for your application with every security update of your base Red Hat build of OpenJDK.

Revised on 2024-05-09 14:53:28 UTC

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