Java ScriptEngine Example

This example demonstrates how to access the Java object from JavaScript statements. Java support the JavaScript access with the ScriptEngineManager class and ScriptEngine interface. Here you will see how we can execute the JavaScript code using the Java API’s.

• Create ScriptEngineManager which tracks the states of all the script engines.
• Create ScriptEngine by using the method getEngineByExtension() define in ScriptEngineManager. Here we pass the parameter “js” to get the JavaScript engine.
• Add the Java object which is used inside the script
• Evaluate the JavaScript by using the ScriptEngine.eval() method

Lets look at the example.

ScriptEngineExample.java

package javabeat.net.script;

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

/**
 * Invoke Java from JavaScript example.
 *
 * @author Krishna
 *
 */
public class ScriptEngineExample {
	public static void main(String[] args) {
		// Create Java array with list of cities
		String cities[] = { "London", "NewYork", "Sydney", "Bangalore",
				"Chennai", "Mumbai" };

		// Create script which accessing Java object
		String script = "var index; " + "var cities = citiesArray;" + ""
				+ "for (index in cities) { " + "println(cities[index]);" + "}";

		// Create ScriptEngine
		ScriptEngineManager engineManager = new ScriptEngineManager();
		ScriptEngine engine = engineManager.getEngineByExtension("js");

		// Add Java object to script engine
		engine.put("citiesArray", cities);
		try {
			// Evaluate  script using script engine
			engine.eval(script);
		} catch (ScriptException exception) {
			exception.printStackTrace();
		}
	}
}

Output…

London
NewYork
Sydney
Bangalore
Chennai
Mumbai

javax.script.ScriptException

If you miss any syntax in the script, you would get the following exception.

javax.script.ScriptException: sun.org.mozilla.javascript.internal.EvaluatorException: missing ( after for (<Unknown source>#1) in <Unknown source> at line number 1
	at com.sun.script.javascript.RhinoScriptEngine.eval(Unknown Source)
	at com.sun.script.javascript.RhinoScriptEngine.eval(Unknown Source)
	at javax.script.AbstractScriptEngine.eval(Unknown Source)
	at javabeat.net.script.ScriptEngineExample.main(ScriptEngineExample.java:31)
Caused by: sun.org.mozilla.javascript.internal.EvaluatorException: missing ( after for (<Unknown source>#1)
	at sun.org.mozilla.javascript.internal.DefaultErrorReporter.runtimeError(Unknown Source)
	at sun.org.mozilla.javascript.internal.DefaultErrorReporter.error(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.addError(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.addError(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.reportError(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.reportError(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.reportError(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.forLoop(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.statementHelper(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.statement(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.parse(Unknown Source)
	at sun.org.mozilla.javascript.internal.Parser.parse(Unknown Source)
	at sun.org.mozilla.javascript.internal.Context.compileImpl(Unknown Source)
	at sun.org.mozilla.javascript.internal.Context.compileReader(Unknown Source)
	at sun.org.mozilla.javascript.internal.Context.compileReader(Unknown Source)
	at sun.org.mozilla.javascript.internal.Context.evaluateReader(Unknown Source)
	... 4 more