Chapter 3. Creating a custom Java runtime environment for modular applications You can create a custom Java runtime environment from a modular application by using the jlink tool. Prerequisites Install Installing Red Hat build of OpenJDK on RHEL using an archive . Note For best results, use portable Red Hat binaries as a basis for a Jlink runtime, because these binaries contain bundled libraries. Procedure Create a simple Hello World application by using the Logger class. Check the base Red Hat build of OpenJDK 21 binary exists in the jdk-17 folder: Create a directory for your application: 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!"); } } Create a file called hello-example/module-info.java and include the following code in the file: module sample { requires java.logging; } Compile your application: Run your application without a custom JRE: The example shows the base Red Hat build of OpenJDK requiring 311 MB to run a single class. (Optional) You can inspect the Red Hat build of OpenJDK and see many non-required modules for your application: 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. Create your application module: Create a custom JRE with the required modules and a custom application launcher for your application: List the modules of the produced custom JRE. Observe that only a fraction of the original Red Hat build of OpenJDK remains. 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. Launch the application using the hello launcher: 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

Commands:
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)
mkdir -p hello-example/sample
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!"); } }
module sample { requires java.logging; }
./jdk-17/bin/javac -d example USD(find hello-example -name \*.java)
./jdk-17/bin/java -cp example sample.HelloWorld Mar 09, 2021 10:48:59 AM sample.HelloWorld main INFO: Hello World!
du -sh jdk-17/ 313M jdk-17/
./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
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
./jdk-17/bin/jlink --launcher hello=sample/sample.HelloWorld --module-path sample-module --add-modules sample --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 sample@1.0.0
./custom-runtime/bin/hello Jan 14, 2021 12:13:26 PM HelloWorld main INFO: Hello World!