Java 1.8 + JavaScript Engine Nashorn + Debugging javascript…

Introduction

This is an extremely quick tutorial about using javascript engine (nashorn) usage in Java 1.8

These are the versions of apis and frameworks etc. used;

• Java 1.8
• JUnit 4.11
• IntelliJ IDEA 13.1.4

WARNING: Using java versions below 8 will cause java.lang.NullPointerException as nashorn javascript engine comes with java 8.

Within this tutorial you will see

• Testing (Kind of encouraging test driven development)
• Creating and using nashorn javascirpt engine
• Calling javascript functions from java
• Calling java methods from javascript
• Debugging javascript file using IntelliJ IDEA

 

Project Structure

INFO: Using maven is not really necessary for this project as all, infact JUnit is the only dependency, nashorn comes with jdk bundle. It is besically just an encouragement.

Dependencies

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>info.hevi.learn</groupId>
	<artifactId>javascriptengine</artifactId>
	<version>1.0</version>

	<description>simple javascript engine tutorial with debugging</description>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <junit.version>4.11</junit.version>
    </properties>

	<dependencies>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

</project>

Code

Test File(MainTest.java)

public class MainTest {

    public String getName(){
        return "hevi.info";
    }

    @Test
    public void testScript() {
        ScriptEngineManager engineManager = new ScriptEngineManager();
        ScriptEngine scriptEngine = engineManager.getEngineByName("nashorn");

        String fileName = "src/main/resources/jsfile.js";
        String functionName = "doIt";
        try {

            scriptEngine.eval("load('" + fileName + "');");
            Invocable inv = (Invocable) scriptEngine;

            String retValue = (String) inv.invokeFunction(functionName, new MainTest());

            System.out.println(fileName + "@" + functionName + " returned " + retValue);

        } catch (ScriptException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}

 

JavaScript File(jsfile.js)

function doIt(param) {
    var message = "hello world " + param.getName() + "!";
    return message;
}

 

So what happenes above is that doIt javascript function is called fully parametric, and pass MainTest instance as a parameter to the method;

inv.invokeFunction(functionName, new MainTest())

The doIt function calles getName() method which corresponds to a java method defined in MainTest class.

 

Debugging

Debugging is as just easy as debugging java files using IntelliJ IDEA 13.1. Here you can find here the IntelliJ blog for the debugging feature. The only point is that you suppose to use “nashorn” engine instead of  raw “javascript” for creating scprint engine as below;

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

Unfortunatelly java 8 is the requirement here.

 

Download Source Code

Download project – javajavascriptengine.zip