How do I evaluate or execute a script file?

By Wayan in Scripting 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>
        <!--https://search.maven.org/remotecontent?filepath=org/graalvm/js/js/21.3.0/js-21.3.0.jar-->
        <groupId>org.graalvm.js</groupId>
        <artifactId>js</artifactId>
        <version>21.3.0</version>
    </dependency>
    <dependency>
        <!--https://search.maven.org/remotecontent?filepath=org/graalvm/js/js-scriptengine/21.3.0/js-scriptengine-21.3.0.jar-->
        <groupId>org.graalvm.js</groupId>
        <artifactId>js-scriptengine</artifactId>
        <version>21.3.0</version>
    </dependency>
</dependencies>

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