How To Javascript In Java

In this blog post, we will learn how to use JavaScript within a Java application. This can be incredibly useful when you need to run scripts dynamically, evaluate expressions or just make use of JavaScript’s powerful features within your Java application.

To achieve this, we will be using the ScriptEngine and ScriptEngineManager classes from the javax.script package. These classes are a part of the Java Scripting API, which allows for scripting languages to be embedded within Java applications.

Setting Up the Script Engine

First, we need to set up the ScriptEngine to use JavaScript. We will be using the Nashorn JavaScript engine that is built into Java. Nashorn is a high-performance JavaScript runtime that is included with JDK 8 and later.

Here’s how to set up the Script Engine:

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

public class JavaScriptInJava {
    public static void main(String[] args) {
        // Create a ScriptEngineManager
        ScriptEngineManager manager = new ScriptEngineManager();

        // Get the JavaScript engine from the manager
        ScriptEngine engine = manager.getEngineByName("JavaScript");

Running JavaScript Code

Now that we have our JavaScript engine set up, we can run JavaScript code within our Java application. We will use the eval() method of the ScriptEngine class to run the code. This method takes a String as an argument and evaluates the JavaScript code contained within it.

Here’s an example of running some JavaScript code:

// Run JavaScript code
try {
    engine.eval("console.log('Hello, World!');");
} catch (ScriptException e) {

Note that the eval() method throws a ScriptException if there’s an error in the provided JavaScript code. Be sure to handle this exception within your application.

Working with JavaScript Variables and Functions

You can also work with JavaScript variables and functions within your Java application. To do this, you’ll need to use the put() and get() methods of the ScriptEngine class.

Here’s an example of creating a JavaScript variable and retrieving its value in Java:

// Create a JavaScript variable
try {
    engine.eval("var x = 10;");

    // Get the value of the JavaScript variable
    Object x = engine.get("x");
    System.out.println("The value of x is: " + x);
} catch (ScriptException e) {

And here’s an example of defining a JavaScript function and calling it from Java:

// Define a JavaScript function
try {
    engine.eval("function add(a, b) { return a + b; }");

    // Call the JavaScript function
    Object result = engine.eval("add(5, 3);");
    System.out.println("The result of the add function is: " + result);
} catch (ScriptException e) {


In this blog post, we’ve seen how to use JavaScript within a Java application using the ScriptEngine and ScriptEngineManager classes from the javax.script package. This can be very helpful when you need to run scripts or evaluate expressions in your Java application using JavaScript’s powerful features.