Java - Learn Java by Examples

How do I get a ScriptEngine by language name and version?

By Wayan in Scripting Last modified: May 24, 2023 0 Comment

This example show you how you can obtain a script engine for a specific language name and specific language version. In the code below we try to obtain script engine instance for ECMAScript version ECMAScript 262 Edition 11.

package org.kodejava.script;

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

public class ScriptEngineSearch {
    public static void main(String[] args) {
        String languageName = "ECMAScript";
        String languageVersion = "ECMAScript 262 Edition 11";

        // Creating a ScriptEngineManager and get the list of available
        // engine factories.
        ScriptEngineManager manager = new ScriptEngineManager();
        List<ScriptEngineFactory> factories = manager.getEngineFactories();

        // We obtain a ScriptEngine from the available factories where
        // the language name is "ECMAScript" and the version is
        // "ECMAScript 262 Edition 11". ECMAScript is the standard name
        // for JavaScript programming language.
        //
        // If we found the desired language we then get the ScriptEngine
        // by calling factory's getScriptEngine() method.
        ScriptEngine engine = null;
        for (ScriptEngineFactory factory : factories) {
            String language = factory.getLanguageName();
            String version = factory.getLanguageVersion();

            if (language.equals(languageName)
                    && version.equals(languageVersion)) {
                engine = factory.getScriptEngine();
                break;
            }
        }

        if (engine != null) {
            try {
                engine.eval("print('Hello There')");
            } 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>

How do I call a specific function of a script?

By Wayan in Scripting Last modified: May 24, 2023 0 Comment

This code demonstrate the use of Invocable interface to invoke a specific function of a script. The Invocable.invokeFunction() takes the function name with or without a parameter as the function’s parameter. The parameter value can be passed as a varargs.

package org.kodejava.script;

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

public class InvokingFunction {
    public static void main(String[] args) {
        String script = """
                function sayHello() {
                   sayHello(null);
                }

                function sayHello(name) {
                   print('Hi there' + ((name == null) ? '!' : ' ' + name + '!'));
                }
                """;

        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByExtension("js");

        try {
            engine.eval(script);

            // Convert / cast the engine into invocable engine.
            Invocable invocableEngine = (Invocable) engine;

            // Invoking sayHello function without parameter.
            invocableEngine.invokeFunction("sayHello");

            // Invoking sayHello function with a parameter.
            invocableEngine.invokeFunction("sayHello", "Jude");
        } catch (ScriptException | NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}

This will output:

Hi there!
Hi there Jude!

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>

How do I evaluate or execute a script file?

By Wayan in Scripting Last modified: May 24, 2023 0 Comment

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>

How do I get the supported scripting engine?

By Wayan in Scripting Last modified: May 24, 2023 0 Comment

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>

How do I get ScriptEngine by engine name?

By Wayan in Scripting Last modified: May 24, 2023 0 Comment

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>