Using Nashorn for scripting in Java applications

Category : Java | Sub Category : Java8 Features | By Prasad Bonam Last updated: 2023-11-13 08:05:32 Viewed : 232

Interoperability between Java and JavaScript is possible through various mechanisms, and the Nashorn JavaScript engine (deprecated in JDK 11) and the newer GraalVM`s JavaScript engine are common choices. Here is an overview of how you can achieve interoperability between Java and JavaScript:

1. Using Nashorn (Deprecated in JDK 11):

Nashorn, the JavaScript engine introduced in Java 8, provides a simple way to interoperate between Java and JavaScript.

Calling Java from JavaScript:

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

public class JavaInteropExample {

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

        try {
            // Exposing a Java object to the JavaScript context
            engine.eval("var JavaClass = Java.type(`com.example.JavaClass`);");
            engine.eval("var javaObject = new JavaClass();");

            // Calling a Java method from JavaScript
            engine.eval("javaObject.javaMethod();");
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
}

Calling JavaScript from Java:

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

public class JavaScriptInteropExample {

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

        try {
            // Evaluating JavaScript code that calls a JavaScript function
            engine.eval("function jsFunction() { return `Hello from JavaScript`; }");
            Object result = engine.eval("jsFunction();");
            System.out.println("Result: " + result);
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
}

2. Using GraalVM:

GraalVM is a high-performance runtime that provides support for multiple languages, including JavaScript. It offers improved performance compared to Nashorn.

Calling Java from JavaScript:

javaCopy code
import org.graalvm.polyglot.Context;
import org.graalvm.polyglot.Value;

public class JavaInteropExample {

    public static void main(String[] args) {
        try (Context context = Context.create()) {
            // Exposing a Java object to the JavaScript context
            context.getBindings("js").putMember("javaObject", new JavaClass());

            // Calling a Java method from JavaScript
            context.eval("js", "javaObject.javaMethod();");
        }
    }
}

Calling JavaScript from Java:

javaCopy code
import org.graalvm.polyglot.Context;
import org.graalvm.polyglot.Value;

public class JavaScriptInteropExample {

    public static void main(String[] args) {
        try (Context context = Context.create()) {
            // Evaluating JavaScript code that calls a JavaScript function
            Value result = context.eval("js", "function jsFunction() { return `Hello from JavaScript`; } jsFunction();");
            System.out.println("Result: " + result);
        }
    }
}

Common Patterns for Interoperability:

• Exposing Java Objects: You can expose Java objects to the JavaScript context, allowing JavaScript code to interact with Java methods and fields.

• Callback Functions: You can pass JavaScript functions as arguments to Java methods, allowing Java code to invoke JavaScript functions.

• Data Exchange: Exchange data between Java and JavaScript by converting between Java and JavaScript data types.

• Exception Handling: Handle exceptions that may occur in either Java or JavaScript code when invoking methods or evaluating scripts.

Considerations:

• Performance: GraalVM generally provides better performance compared to Nashorn. If performance is a critical factor, consider using GraalVM.

• Error Handling: Pay attention to error handling, especially when calling methods or evaluating scripts. Handle exceptions gracefully to ensure robust interoperability.

• Security: Be cautious about exposing sensitive Java objects to JavaScript code. Ensure that proper security measures are in place.

Interoperability between Java and JavaScript can be a powerful tool, allowing developers to leverage the strengths of both languages in a single application. However, it is essential to consider the trade-offs and choose the approach that best fits the requirements of your specific use case.