Nashorn is a JavaScript engine that is built into Java 8 and later versions. It allows developers to embed JavaScript code within Java applications, giving them the ability to execute JavaScript from within their Java programs. This feature can be useful in scenarios where you need to evaluate JavaScript dynamically or interact with existing JavaScript libraries from your Java code.

In this blog post, we will explore the steps required to embed Nashorn in a Java application and demonstrate some practical use cases.

Table of Contents

• Introduction to Nashorn
• Embedding Nashorn in Java
• Executing JavaScript Code
• Interacting with Java from JavaScript
• Conclusion

Introduction to Nashorn

Nashorn is a high-performance JavaScript runtime that enables developers to execute JavaScript code natively within the Java Virtual Machine (JVM). It provides full interoperability between Java and JavaScript, allowing seamless integration between the two languages.

Nashorn supports the ECMAScript 5.1 specification, which includes features such as closures, anonymous functions, and JSON parsing. It also provides access to Java APIs, allowing JavaScript code to interact with Java classes and libraries.

Embedding Nashorn in Java

To use Nashorn in a Java application, you need to include the jdk.nashorn.api.scripting package, which contains the necessary classes and interfaces for interacting with the Nashorn JavaScript engine.

import jdk.nashorn.api.scripting.*;

public class NashornDemo {
    public static void main(String[] args) {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

        // Your Nashorn code goes here
    }
}

In the above example, we create an instance of the ScriptEngineManager to manage the JavaScript engines and retrieve the Nashorn engine using getEngineByName("nashorn").

Executing JavaScript Code

Once you have obtained an instance of the Nashorn engine, you can use it to evaluate JavaScript code from within your Java application.

import jdk.nashorn.api.scripting.*;

public class NashornDemo {
    public static void main(String[] args) {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

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

In the above example, we evaluate the JavaScript code print('Hello, Nashorn!') using the eval() method of the Nashorn engine. This will execute the JavaScript code and print the output to the console.

Interacting with Java from JavaScript

One of the powerful features of Nashorn is the ability to interact with Java classes and libraries from within JavaScript code. This allows you to leverage existing Java functionality and use it seamlessly in your JavaScript applications.

import jdk.nashorn.api.scripting.*;

public class NashornDemo {
    public static void main(String[] args) {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

        try {
            engine.eval("var ArrayList = Java.type('java.util.ArrayList');" +
                        "var list = new ArrayList();" +
                        "list.add('Java');" +
                        "list.add('JavaScript');" +
                        "print(list.get(0))");
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
}

The above code snippet demonstrates how to create and use a Java ArrayList object within JavaScript. We use the Java.type() function to import the ArrayList class, create a new instance, add elements to it, and retrieve the first element using the get() method.

Conclusion

Embedding Nashorn in Java applications provides a powerful way to blend the capabilities of Java and JavaScript, allowing you to execute JavaScript code within your Java programs and seamlessly interact with Java classes and libraries.

By following the steps outlined in this blog post, you can start embedding Nashorn in your Java applications and benefit from its performance and interoperability.

#nashorn #javascript #java