Here you can see how to import a Java class so that you can use the class, creates an instance of it in the scripting environment. We want to print out the current date on the console. For this we need to import the Date class that’s packaged under the java.util package.

In the script we can import the java.util package using the following script let Date = Java.type("java.util.Date").

package org.kodejava.script;

import javax.script.Bindings;
import javax.script.ScriptContext;
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
import java.util.function.Predicate;

public class ImportPackageExample {
    public static void main(String[] args) {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByExtension("js");
        Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
        bindings.put("polyglot.js.allowHostAccess", true);
        bindings.put("polyglot.js.allowHostClassLookup", (Predicate<String>) s -> true);

        try {
            engine.eval(getScript());
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }

    private static String getScript() {
        return """                               
                let Date = Java.type("java.util.Date");
                let today = new Date();
                print(`Today is ${today.toString()}`);
                print(`today is ${today.getClass().getName()}`);
                """;
    }
}

This program prints the following line:

Today is Sun Oct 10 15:15:13 CST 2021
today is java.util.Date

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.graalvm.js</groupId>
        <artifactId>js</artifactId>
        <version>22.3.2</version>
    </dependency>
    <dependency>
        <groupId>org.graalvm.js</groupId>
        <artifactId>js-scriptengine</artifactId>
        <version>22.3.2</version>
    </dependency>
</dependencies>

This example show how to modify Java object from scripting environment. Below we manipulate a collection of string data. To pass data into the scripting engine we use a key-value binding to the script engine.

package org.kodejava.script;

import javax.script.Bindings;
import javax.script.ScriptContext;
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
import java.util.List;
import java.util.ArrayList;

public class ModifiedJavaObjectFromScript {
    public static void main(String[] args) {
        // Creating an array of five colors
        List<String> colors = new ArrayList<>();
        colors.add("White");
        colors.add("Black");
        colors.add("Red");
        colors.add("Green");
        colors.add("Blue");

        // Obtain a ScriptEngine instance.
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByExtension("js");
        Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
        bindings.put("polyglot.js.allowHostAccess", true);

        // Place the colors list into the engine using colorList key.
        // After passing the list into the engine our script will be
        // able to read it.
        engine.put("colorList", colors);

        try {
            engine.eval(getScript());

            // Redisplay the modified version of colors.
            for (String color : colors) {
                System.out.println("In Java: " + color);
            }
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }

    private static String getScript() {
        // Below is our script to read the values of Java List that
        // contains string of colors. We also add some other colors
        // to the list object in the script environment.
        return """
                let index;
                let colors = colorList.toArray();

                for (index in colors) {
                    print(`In script: ${colors[index]}`);
                }

                colorList.add("Yellow");
                colorList.add("Purple");
                colorList.add("Orange");
                """;
    }
}

The output of the code snippet above is:

In script: White
In script: Black
In script: Red
In script: Green
In script: Blue
In Java: White
In Java: Black
In Java: Red
In Java: Green
In Java: Blue
In Java: Yellow
In Java: Purple
In Java: Orange

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.graalvm.js</groupId>
        <artifactId>js</artifactId>
        <version>22.3.2</version>
    </dependency>
    <dependency>
        <groupId>org.graalvm.js</groupId>
        <artifactId>js-scriptengine</artifactId>
        <version>22.3.2</version>
    </dependency>
</dependencies>