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JavaScript on the VM
Rory Preddy
“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
Nashorn and Avatar
invokeDynamic
Rhino
(Separate download)
1.3 1.4
5.0
JDK with Scripting
and built in Rhino
6
7
8
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
• jrunscript
js> 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
• Rhino optimizer not standard with JDK
• Runtime optimization of compilation can be set from -1 to 9
-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
Nashorn
InvokeDynamic
Bytecode operations that were available before JDK version 7:
Opcode
Usage
Invokestatic
For static methods
Invokevirtual
For non-private instance methods
Invokespecial
For private instance
Invokeinterface For the receiver that implements the interface
InvokeStatic
The challenge
• JavaScript is dynamic
– Things can change at runtime
• For example, what is the type of:
var x = 500000;
• x *= 500000;
And now?
Enter JSR 292
• 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!
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
Nashorn- Command Line
> jjs
jjs> var x = 10, y = 20;
jjs> x + y;
>>30
Or
> jjs example.js
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)
Avatar.js (Node.jar)
Supported module highlights
• Implements the Node
model and API on the
JVM
• Supports most Node
modules
Avatar+ EJB = Avatar EE
Summary – JavaScript Why bother?
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
Demo
Demo overview
• JavaScript coding Demo
• Credit card validation
• Avatar Demo
• Show and tell
• Fibonacci numbers
• Interest calculation
• Groovy Examples