jlink Hello World

1 Create the directory structure

mkdir -p hello-example/sample

2 Create the file hello-example/sample/HelloWorld.java

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!");
    }
}

3 create the module info file hello-example/module-info.java

module sample
{
    requires java.logging;
}

4 Compiling

./jdk-21/bin/javac -d example $(find hello-example -name \*.java)

5 Running

5.1 Without a custom JRE

./jdk-21/bin/java -cp example sample.HelloWorld

5.2 Building a custom JRE

Checking the original JVM size

du -sh jdk-21/

Creating an application module

mkdir sample-module
```bash

```bash
./jdk-21/bin/jmod create --class-path example/ --main-class sample.HelloWorld --module-version 1.0.0 -p example sample-module/hello.jmod

Creating a custom JRE with the required modules and a custom application launcher for the application

./jdk-21/bin/jlink --launcher hello=sample/sample.HelloWorld --module-path sample-module --add-modules sample --output custom-runtime

Checking the size of the newly created custom JRE

du -sh custom-runtime

Checking the modules of the custom JRE

./custom-runtime/bin/java --list-modules

Launch the application using the hello launcher

./custom-runtime/bin/hello