Java Nashorn is a JavaScript engine that is integrated into Java since JDK 8. It allows you to execute JavaScript code within your Java applications. This can be useful in scenarios where you want to leverage existing JavaScript libraries or execute custom JavaScript logic.

In this article, we will explore how to run JavaScript code using Java Nashorn.

Setting up Java Nashorn

Before you start running JavaScript code, you need to make sure you have Java Nashorn set up in your Java project. In JDK 8 and above, Nashorn comes bundled with the Java runtime, so there is no additional setup required.

Running JavaScript code

To run JavaScript code using Nashorn, you will need to follow these steps:

1. Create an instance of the javax.script.ScriptEngineManager class.

ScriptEngineManager engineManager = new ScriptEngineManager();

1. Retrieve the Nashorn scripting engine using the getEngineByName method.

ScriptEngine engine = engineManager.getEngineByName("nashorn");

1. Execute JavaScript code using the eval method on the scripting engine.

String javascriptCode = "var message = 'Hello, World!'; message";
Object result = engine.eval(javascriptCode);
System.out.println(result);

In the example above, we have created a simple JavaScript code that assigns a value to a variable and then returns that variable. The eval method executes the JavaScript code and returns the result.

You can also pass JavaScript code from external files using the eval method. Instead of passing a string containing the JavaScript code, you can pass a FileReader object pointing to the file.

Reader scriptReader = new FileReader("path/to/javascript.js");
engine.eval(scriptReader);

Interacting between Java and JavaScript

Java Nashorn allows you to interact between Java and JavaScript seamlessly. You can pass values between Java and JavaScript, invoke Java methods from JavaScript, and vice versa.

To pass values from Java to JavaScript, you can use the put method on the scripting engine:

engine.put("name", "John");

Then, you can access the name variable in your JavaScript code:

String javascriptCode = "name";
Object result = engine.eval(javascriptCode);
System.out.println(result);

To invoke Java methods from JavaScript, you can expose Java objects to the scripting engine using the put method. Then, you can call Java methods by referencing the exposed objects in your JavaScript code.

SomeJavaObject javaObject = new SomeJavaObject();
engine.put("javaObject", javaObject);

In JavaScript:

javaObject.someMethod();

Conclusion

Java Nashorn provides a seamless way to run JavaScript code within Java applications. You can leverage this feature to extend the functionality of your Java applications or integrate existing JavaScript code libraries.

By following the steps outlined in this article, you should be able to run JavaScript code using Java Nashorn and interact between Java and JavaScript effortlessly.

#java #javascript