How do I evaluate or execute a script file?

This example demonstrated how to evaluate script that stored on a file. As we know that the eval() method can also accept a Reader object we can then read the script file using FileReader and pass it as the parameter to the eval() method of the ScriptEngine for further evaluation.

package org.kodejava.script;

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
import java.io.File;
import java.io.Reader;
import java.io.FileReader;
import java.io.FileNotFoundException;

public class EvalScriptFile {
    public static void main(String[] args) {
        // Obtaining ECMAScript / JavaScript ScriptEngine.
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("ECMAScript");

        try {
            // Create an instance of File object that point to our
            // scripting file. An create a FileReader to read the
            // file to be passed to the ScriptEngine.eval() method.
            //
            // The file need to be placed in the same folder with
            // our class so it enable to read it. We can define the
            // full path to the file also to make easier for the
            // Reader to find it.
            File script = new File("helloworld.js");
            Reader reader = new FileReader(script);

            engine.eval(reader);
        } catch (FileNotFoundException | ScriptException e) {
            e.printStackTrace();
        }
    }
}

Our helloworld.js file.

console.log('Hello World');

for (let i = 0; i <= 10; i++) {
    console.log(`i = ${i}`);
}

The output of the code snippet:

Hello World
i = 0
i = 1
i = 2
i = 3
i = 4
i = 5
i = 6
i = 7
i = 8
i = 9
i = 10

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>

Maven Central Maven Central

How do I get the supported scripting engine?

package org.kodejava.script;

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngineFactory;
import java.util.List;

public class GetSupportedScriptingEngine {
    public static void main(String[] args) {
        // Creating an instance of ScriptEngineManager an get the list
        // of available ScriptEngineFactory.
        ScriptEngineManager manager = new ScriptEngineManager();
        List<ScriptEngineFactory> factories = manager.getEngineFactories();

        for (ScriptEngineFactory factory : factories) {
            System.out.println(
                    "EngineName      = " + factory.getEngineName());
            System.out.println(
                    "EngineVersion   = " + factory.getEngineVersion());
            System.out.println(
                    "LanguageName    = " + factory.getLanguageName());
            System.out.println(
                    "LanguageVersion = " + factory.getLanguageVersion());
            System.out.println(
                    "Extensions      = " + factory.getExtensions());
            System.out.println();

            List<String> names = factory.getNames();
            for (String name : names) {
                System.out.println("Engine Alias = " + name);
            }
        }
    }
}

The code above produces the following information.

EngineName      = Graal.js
EngineVersion   = Development Build
LanguageName    = ECMAScript
LanguageVersion = ECMAScript 262 Edition 11
Extensions      = [js, mjs]

Engine Alias = js
Engine Alias = JS
Engine Alias = JavaScript
Engine Alias = javascript
Engine Alias = ECMAScript
Engine Alias = ecmascript
Engine Alias = Graal.js
Engine Alias = graal.js
Engine Alias = Graal-js
Engine Alias = graal-js
Engine Alias = Graal.JS
Engine Alias = Graal-JS
Engine Alias = GraalJS
Engine Alias = GraalJSPolyglot

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>

Maven Central Maven Central

How do I get ScriptEngine by engine name?

This example shows how to get an instance of ScriptEngine by the engine name. Below we are trying to obtain the GraalVM JavaScript engine.

package org.kodejava.script;

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

public class GettingScriptEngineByName {
    public static void main(String[] args) {
        ScriptEngineManager manager = new ScriptEngineManager();

        // Obtain an instance of ScriptEngine using the engine name. For
        // example, we get a GraalVM JavaScript engine.
        ScriptEngine engine = manager.getEngineByName("graal.js");

        try {
            engine.eval("print('Hello World');");
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
}

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>

Maven Central Maven Central

How do I evaluate a simple script?

The code below will evaluate a simple JavaScript that produces a “Hello World” message. To evaluate the script, the ScriptEngine provides us with some overloaded eval() methods, for instance an eval() methods that accept the script in string or in Reader object.

package org.kodejava.script;

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

public class EvaluatingScript {
    public static void main(String[] args) {
        // Obtaining the GraalVM Javascript engine
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("graal.js");

        try {
            // Evaluating a simple script
            engine.eval("print('Hello World')");
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
}

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>

Maven Central Maven Central

How do I create an instance of ScriptEngine class for JavaScript?

This example demonstrates how to create a JavaScript interpreter or the ScriptEngine to run JavaScript in Java. The classes related to scripting is packaged under the javax.script.* package. In this example we show you how to create the JavaScript engine by using the engine extension.

package org.kodejava.script;

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

public class GettingJavaScriptEngine {
    public static void main(String[] args) {
        // Creating an instance of ScriptManager. With ScriptManager in hand we
        // can create an interpreter or ScriptEngine to run JavaScript.
        ScriptEngineManager manager = new ScriptEngineManager();

        // Calling manager.getEngineByExtension("js") returns a ScriptEngine
        // implementation for JavaScript engine.
        ScriptEngine engine = manager.getEngineByExtension("js");

        // Do something with the script engine.
        System.out.println("Engine = " + engine);
    }
}

The output of the code snippet:

Engine = com.oracle.truffle.js.scriptengine.GraalJSScriptEngine@56235b8e

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>

Maven Central Maven Central