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 : 142



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:

java
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:

java
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:

java
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:

java
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.

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