Using jlink to customize Java runtime environment

OpenJDK 11

Red Hat Customer Content Services

Abstract

OpenJDK 11 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 and use customize Java runtime image using jlink.

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Chapter 2. Creating a custom Java runtime environment for non-modular applications

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

Prerequisites

Procedure

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

    1. You have the base OpenJDK 11 available in the jdk-11 folder:

      $ ls jdk-11
      bin  conf  demo  include  jmods  legal  lib  man  NEWS  release
      $ ./jdk-11/bin/java -version
      openjdk version "11.0.10" 2021-01-19 LTS
      OpenJDK Runtime Environment 18.9 (build 11.0.10+9-LTS)
      OpenJDK 64-Bit Server VM 18.9 (build 11.0.10+9-LTS, mixed mode)
    2. Create a directory for your application:

      $ mkdir -p hello-example/sample
    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!");
          }
      }
    4. Compile your application:

      $ ./jdk-11/bin/javac -d . $(find hello-example -name \*.java)
    5. Run your application without a custom JRE:

      $ ./jdk-11/bin/java sample.HelloWorld
      Mar 09, 2021 10:48:59 AM sample.HelloWorld main
      INFO: Hello World!

      In this case, the base OpenJDK takes 311 MB to run a single class.

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

      $ du -sh jdk-11/
      313M	jdk-11/
      $ ./jdk-11/bin/java --list-modules
      java.base@11.0.10
      java.compiler@11.0.10
      java.datatransfer@11.0.10
      java.desktop@11.0.10
      java.instrument@11.0.10
      java.logging@11.0.10
      java.management@11.0.10
      java.management.rmi@11.0.10
      java.naming@11.0.10
      java.net.http@11.0.10
      java.prefs@11.0.10
      java.rmi@11.0.10
      java.scripting@11.0.10
      java.se@11.0.10
      java.security.jgss@11.0.10
      java.security.sasl@11.0.10
      java.smartcardio@11.0.10
      java.sql@11.0.10
      java.sql.rowset@11.0.10
      java.transaction.xa@11.0.10
      java.xml@11.0.10
      java.xml.crypto@11.0.10
      jdk.accessibility@11.0.10
      jdk.aot@11.0.10
      jdk.attach@11.0.10
      jdk.charsets@11.0.10
      jdk.compiler@11.0.10
      jdk.crypto.cryptoki@11.0.10
      jdk.crypto.ec@11.0.10
      jdk.dynalink@11.0.10
      jdk.editpad@11.0.10
      jdk.hotspot.agent@11.0.10
      jdk.httpserver@11.0.10
      jdk.internal.ed@11.0.10
      jdk.internal.jvmstat@11.0.10
      jdk.internal.le@11.0.10
      jdk.internal.opt@11.0.10
      jdk.internal.vm.ci@11.0.10
      jdk.internal.vm.compiler@11.0.10
      jdk.internal.vm.compiler.management@11.0.10
      jdk.jartool@11.0.10
      jdk.javadoc@11.0.10
      jdk.jcmd@11.0.10
      jdk.jconsole@11.0.10
      jdk.jdeps@11.0.10
      jdk.jdi@11.0.10
      jdk.jdwp.agent@11.0.10
      jdk.jfr@11.0.10
      jdk.jlink@11.0.10
      jdk.jshell@11.0.10
      jdk.jsobject@11.0.10
      jdk.jstatd@11.0.10
      jdk.localedata@11.0.10
      jdk.management@11.0.10
      jdk.management.agent@11.0.10
      jdk.management.jfr@11.0.10
      jdk.naming.dns@11.0.10
      jdk.naming.ldap@11.0.10
      jdk.naming.rmi@11.0.10
      jdk.net@11.0.10
      jdk.pack@11.0.10
      jdk.rmic@11.0.10
      jdk.scripting.nashorn@11.0.10
      jdk.scripting.nashorn.shell@11.0.10
      jdk.sctp@11.0.10
      jdk.security.auth@11.0.10
      jdk.security.jgss@11.0.10
      jdk.unsupported@11.0.10
      jdk.unsupported.desktop@11.0.10
      jdk.xml.dom@11.0.10
      jdk.zipfs@11.0.10

      Sample Hello World application has very few dependencies. You can use jlink to create custom runtime images for your application. These images help you run your application with only required OpenJDK dependencies.

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

    $ ./jdk-11/bin/jdeps -s ./sample/HelloWorld.class
    HelloWorld.class -> java.base
    HelloWorld.class -> java.logging
  3. Build a custom java runtime image for your application:

    $ ./jdk-11/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@11.0.10
    java.logging@11.0.10
    Note

    The size of your custom java runtime image is being reduced to 50M runtime image from 313M 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!

    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

Rebuild the custom java runtime images for your application with every security update of your base OpenJDK.

Chapter 3. Creating a custom Java runtime environment for modular applications

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

Prerequisites

Procedure

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

    1. You have the base OpenJDK 11 available in the jdk-11 folder:

      $ ls jdk-11
      bin  conf  demo  include  jmods  legal  lib  man  NEWS  release
      $ ./jdk-11/bin/java -version
      openjdk version "11.0.10" 2021-01-19 LTS
      OpenJDK Runtime Environment 18.9 (build 11.0.10+9-LTS)
      OpenJDK 64-Bit Server VM 18.9 (build 11.0.10+9-LTS, mixed mode)
    2. Create a directory for your application:

      $ mkdir -p hello-example/sample
    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!");
          }
      }
    4. Create hello-example/module-info.java file with the following content:

      module sample
      {
          requires java.logging;
      }
    5. Compile your application:

      $ ./jdk-11/bin/javac -d example $(find hello-example -name \*.java)
    6. Run your application without a custom JRE:

      $ ./jdk-11/bin/java -cp example sample.HelloWorld
      Mar 09, 2021 10:48:59 AM sample.HelloWorld main
      INFO: Hello World!

      In this case, the base OpenJDK takes 311 MB to run a single class.

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

      $ du -sh jdk-11/
      313M	jdk-11/
      $ ./jdk-11/bin/java --list-modules
      java.base@11.0.10
      java.compiler@11.0.10
      java.datatransfer@11.0.10
      java.desktop@11.0.10
      java.instrument@11.0.10
      java.logging@11.0.10
      java.management@11.0.10
      java.management.rmi@11.0.10
      java.naming@11.0.10
      java.net.http@11.0.10
      java.prefs@11.0.10
      java.rmi@11.0.10
      java.scripting@11.0.10
      java.se@11.0.10
      java.security.jgss@11.0.10
      java.security.sasl@11.0.10
      java.smartcardio@11.0.10
      java.sql@11.0.10
      java.sql.rowset@11.0.10
      java.transaction.xa@11.0.10
      java.xml@11.0.10
      java.xml.crypto@11.0.10
      jdk.accessibility@11.0.10
      jdk.aot@11.0.10
      jdk.attach@11.0.10
      jdk.charsets@11.0.10
      jdk.compiler@11.0.10
      jdk.crypto.cryptoki@11.0.10
      jdk.crypto.ec@11.0.10
      jdk.dynalink@11.0.10
      jdk.editpad@11.0.10
      jdk.hotspot.agent@11.0.10
      jdk.httpserver@11.0.10
      jdk.internal.ed@11.0.10
      jdk.internal.jvmstat@11.0.10
      jdk.internal.le@11.0.10
      jdk.internal.opt@11.0.10
      jdk.internal.vm.ci@11.0.10
      jdk.internal.vm.compiler@11.0.10
      jdk.internal.vm.compiler.management@11.0.10
      jdk.jartool@11.0.10
      jdk.javadoc@11.0.10
      jdk.jcmd@11.0.10
      jdk.jconsole@11.0.10
      jdk.jdeps@11.0.10
      jdk.jdi@11.0.10
      jdk.jdwp.agent@11.0.10
      jdk.jfr@11.0.10
      jdk.jlink@11.0.10
      jdk.jshell@11.0.10
      jdk.jsobject@11.0.10
      jdk.jstatd@11.0.10
      jdk.localedata@11.0.10
      jdk.management@11.0.10
      jdk.management.agent@11.0.10
      jdk.management.jfr@11.0.10
      jdk.naming.dns@11.0.10
      jdk.naming.ldap@11.0.10
      jdk.naming.rmi@11.0.10
      jdk.net@11.0.10
      jdk.pack@11.0.10
      jdk.rmic@11.0.10
      jdk.scripting.nashorn@11.0.10
      jdk.scripting.nashorn.shell@11.0.10
      jdk.sctp@11.0.10
      jdk.security.auth@11.0.10
      jdk.security.jgss@11.0.10
      jdk.unsupported@11.0.10
      jdk.unsupported.desktop@11.0.10
      jdk.xml.dom@11.0.10
      jdk.zipfs@11.0.10

      Sample Hello World application has very few dependencies. You can use jlink to create custom runtime images for your application. These images help you run your application with only required OpenJDK dependencies.

  2. Create your application module:

    $ mkdir sample-module
    $ ./jdk-11/bin/jmod create --class-path example/ --main-class sample.HelloWorld --module-version 1.0.0 -p example sample-module/hello.jmod
  3. Create a custom JRE with the required modules and a custom application launcher for your application.

    $ ./jdk-11/bin/jlink --launcher hello=sample/sample.HelloWorld --module-path sample-module --add-modules sample --output custom-runtime
  4. List the modules of the produced custom JRE.

    Observe that only a fraction of the original OpenJDK remains.

    $ du -sh custom-runtime
    50M	custom-runtime/
    $ ./custom-runtime/bin/java --list-modules
    java.base@11.0.10
    java.logging@11.0.10
    sample@1.0.0
    Note

    The size of your custom java runtime image is being reduced to 50M runtime image from 313M 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!

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

    You can distribute your application bundled with the custom runtime in custom-runtime. It includes your application.

Note

Rebuild the custom java runtime images for your application with every security update of your base OpenJDK.

Revised on 2021-10-25 12:31:50 UTC

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