Rory Preddy

JavaScript on the VM

“Any application that can be written in JavaScript, will eventually be written in JavaScript”- Jeff Atwood (founder, stackoverflow.com)

What we going to discuss today

• Rhino on JDK 1.6 & 1.7

• Nashorn on Java 8

• Avatar.js - aka Node via Java

In the Beginning - JavaScript

• Developed by Netscape as a portable version of Java offering a lightweight interpreted language

• Developed under the name Mocha, officially released as LiveScript in September 1995,

• Renamed JavaScript in December 1995 as a marketing ploy to leverage off Java's popularity

• Even reserved Java’s keywords

• Standardized by ECMA International

JavaScript/Java Timeline

1.3 1.4 5.0 6 7 8

Rhino(Separate download)

invokeDynamic

Nashorn and Avatar

JDK with Scripting and built in Rhino

Rhino

In the Beginning - Rhino

• In 1997 Netscape wanted a browser written fully in Java and so it needed an implementation of JavaScript written in Java.

• Code named "Javagator", project was canned but engine lived on

• Compiles JavaScript code to Java bytecodes in either Interpreted or generated Java class files.

• Suffers from:• Slow compile time• Memory leaks• Very unsecure!!!

Using Rhino - Command line and REPL

• jrunscript -e "print('hello world')“

• jrunscript -l js -f helloWorld.js

• jrunscriptjs> print('Hello World\n');>>Hello World

Using Scripting API - background

• “javax.script” package

• Use any JSR-223 compliant scripting language.

• Java SE 6 & 7 include Scripting API and Mozilla Rhino as default engine

• Extensive list of available engines: Python, Ruby, PHP, Groovy …

Script API Basics

1) Create a ScriptEngineManager object.

ScriptEngineManager factory = new ScriptEngineManager();

2) Get a ScriptEngine object from the manager.

ScriptEngine engine = factory.getEngineByName("JavaScript");

3) Evaluate script using the ScriptEngine's eval methods.

engine.eval("print('Hello, World')");

Invoking Script Functions and Methods

String script = "function hello(name) {" + " return 'Hello, ' +

name; " + }";

engine.eval(script);

Invocable inv = (Invocable) engine; String val = (String) inv.invokeFunction("hello", "BBD!!"); System.out.println(val);

>>Hello, BBD!!

Binding Java objects into script space

Bindings bindings = new SimpleBindings();

bindings.put("author", new Person("Rory", "Preddy", 34));

engine.eval("print('Name:' + author.name)", bindings);

>>Name: Rory

Callbacks

… engine.put("cb", new JsCallback()); engine.eval("println('Doing something in javascript here first');" + "cb.apply('bar');"); }

public void apply(String s){ System.out.println("Back in java code here: " + s); }

…

>>Doing something in javascript here first>>Back in java code here: bar

Implementing Java Interfaces by Scripts

String script = "function run() { " + "println('run called'); " + "}";engine.eval(script);

Runnable r = ((Invocable) engine).getInterface(Runnable.class);

new Thread(r).start();

>>run called

Java Interfaces in JavaScript

var r = new java.lang.Runnable() { run: function() { print("running...\n"); }};

var th = new java.lang.Thread(r);th.start();

>>running…

Compiling

engine.put("counter", 0);Compilable compEngine = (Compilable) engine; CompiledScript script = compEngine.compile(“ function count(){

counter=counter+1; return counter;};

count();");System.out.println(script.eval());System.out.println(script.eval());…

>>1.0>>2.0

Compiling with Rhino

cat test.js

java.lang.System.out.println("hi, mom!");

java org.mozilla.javascript.tools.jsc.Main test.js

ls *.class

test.class

java test

>>hi, mom!

Optimization

-1

Interpretive mode is always used. No class files are generated,

0

Basic Compilation.No optimizations are performed. The compiler runs fastest in this mode, but the generated byte code is less efficient

1-9

All optimizations are performed. Java Class Files generated

• Rhino optimizer not standard with JDK

• Runtime optimization of compilation can be set from -1 to 9

Nashorn

InvokeDynamic

Opcode Usage

Invokestatic For static methods

Invokevirtual For non-private instance methods

Invokespecial For private instance

Invokeinterface

For the receiver that implements the interface

Bytecode operations that were available before JDK version 7:

InvokeStatic

• JavaScript is dynamic– Things can change at runtime

• For example, what is the type of:var x = 500000;

• x *= 500000; And now?

The challenge

• Based on an experimental project, the Da Vinci Machine

• Adds two new concepts to the JVM:– invokedynamic bytecode instruction– MethodHandles

• The first bytecode extension since 1999!

Enter JSR 292

InvokeDynamic

Nashorn

• NO COMILATION! - Compiles JavaScript directly into byte code

• 20x faster than uncompiled Rhino• Better typing• Smaller footprint• 100% compliant with ECMA-262 5.1 • Standard JSR-223 syntax

> jjsjjs> var x = 10, y = 20;jjs> x + y;

>>30

Or

> jjs example.js

Nashorn- Command Line

Rhino VS Nashorn - Types

…engine.eval("function test() { return 1; };");Object result = ((Invocable)engine).invokeFunction("test");System.out.println(result.getClass().getName());

//Rhino output>>>java.lang.Double

// Nashorn output>>>java.lang.Integer

Rhino VS Nashorn - Exceptions

// in rhino.js !!try { java.lang.System.loadLibrary(null)} catch (e) {

print(e instanceof java.lang.NullPointerException)

// false!!

print(e.javaException instanceof java.lang.NullPointerException)

// true}

Lambdas in Nashorn

var list = java.util.Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8);var odd = list.stream().filter(function(i) { return i % 2 == 0;});odd.forEach(function(i) { print(">>> " + i);});

>>> 2>>> 4>>> 6>>> 8

Nashorn Vs Rhino

Avatar.js

Node

Avatar.js (Node.jar)

• Implements the Node model and API on the JVM

• Supports most Node modules

Supported module highlights

Avatar.js (Node.jar)

Avatar+ EJB = Avatar EE

Why you care

• Server-side JavaScript • Leverage Existing

JavaScript Libraries• Cross Platform scripting –

Rhino runs on Android• Fast performance with

Nashorn• Leverage new Node

Libraries with Nashorn

Why Oracle cares

• Atwood’s law• Node.js

– A real threat to Java’s server-side growth

• Let developers handle typing with invokedynamic– Jruby, Jython

Summary – JavaScript Why bother?

Demo

Demo overview

• JavaScript coding Demo• Credit card validation

• Avatar Demo

• Show and tell• Fibonacci numbers• Interest calculation• Groovy Examples