Java Nashorn JavaScript Engine: Integrate JavaScript with High Performance

Discover the Nashorn JavaScript Engine, introduced in Java 8, a high-performance engine that compiles JavaScript into bytecode for enhanced execution speed. Learn how Nashorn enables you to embed JavaScript within Java, execute JavaScript from command-line tools, and seamlessly call Java methods within JavaScript code using the jjs command.

Java - Nashorn JavaScript Engine

Introduction to Nashorn

Nashorn is a powerful and high-performance JavaScript engine introduced in Java 8. It replaces the older Rhino engine and offers performance improvements of up to 10 times faster. Nashorn compiles JavaScript code directly into bytecode, leveraging dynamic features introduced in Java 7 to enhance performance.

With Nashorn, you can execute JavaScript code from command-line tools, embed JavaScript in Java files, and call JavaScript methods from Java code. Additionally, using the jjs command, you can call Java methods within JavaScript code.

Execute JavaScript via Command-Line Tools

Java 8 introduces the jjs command-line tool to execute JavaScript code. The tool can interpret both JavaScript files and code snippets. Additionally, you can invoke Java methods from JavaScript using this tool.

Example: Running a JavaScript File

First, create and save a file sample.js in the C:\JAVA folder with the following content:

print('Hello World!');

To execute the JavaScript file, open the console and run:

C:\JAVA>jjs sample.js

Output:

Now, update the file to include a function and call it:

function sayMessage(){
print('Hello World!');	
}
sayMessage();
    

Run the updated file:

C:\JAVA>jjs sample.js

Output:

Execute JavaScript Directly in Command Prompt

You can also use jjs interactively by typing it in the command prompt:

C:\JAVA>jjs
jjs> print("Hello, World!")
jjs> quit()
    

Output:

Passing Arguments to jjs

You can pass command-line arguments to jjs, which are stored in the arguments array.

Example:

Run the following command in the console:

C:\JAVA>jjs -- a b c

Output:

Calling JavaScript from Java

Using the ScriptEngineManager class (introduced in Java 6), you can load the Nashorn engine and execute JavaScript code from within Java. Java variables can also be passed into JavaScript.

Example:

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

public class Java8Tester {

public static void main(String args[]) {
    ScriptEngineManager scriptEngineManager = new ScriptEngineManager();
    ScriptEngine nashorn = scriptEngineManager.getEngineByName("nashorn");
    
    String name = "Mahesh";
    Integer result = null;
    
    try {
        nashorn.eval("print('" + name + "')");
        result = (Integer) nashorn.eval("10 + 2");
    } catch(ScriptException e) {
        System.out.println("Error executing script: " + e.getMessage());
    }
    System.out.println(result.toString());
}
}
    

Output:

Calling Java from JavaScript

With the jjs tool, you can also call Java code from within JavaScript. In this example, we'll use the BigDecimal class in JavaScript to perform calculations.

Example:

Create and save sample.js:

var BigDecimal = Java.type('java.math.BigDecimal');

function calculate(amount, percentage) {
var result = new BigDecimal(amount).multiply(new BigDecimal(percentage))
    .divide(new BigDecimal("100"), 2, BigDecimal.ROUND_HALF_EVEN);
return result.toPlainString();
}

var result = calculate(568000000000000000023,13.9);
print(result);
    

Output: