talk on rhino and javascript engines in java

1. Rory Preddy
JavaScript on the VM

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

4. 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

5. JavaScript/Java Timeline
1.3 1.4 5.0 6 7 8
Rhino
(Separate download)
invokeDynamic
Nashorn
JDK with Scripting
and built in Rhino

6. Rhino

7. 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!!!

8. Using Rhino - Command line and REPL
• jrunscript -e "print('hello world')“
• jrunscript -l js -f helloWorld.js
• jrunscript
js> print('Hello Worldn');
>>Hello World

9. 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 …

10. 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')");

11. 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!!

12. 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

13. 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

14. 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

15. 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…

16. 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

17. 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!

18. 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

19. Nashorn

20. 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:

21. InvokeStatic

22. • JavaScript is dynamic
– Things can change at runtime
• For example, what is the type of:
var x = 500000;
• x *= 500000; And now?
The challenge

23. • 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

24. InvokeDynamic

25. Nashorn
• Default script Engine in Java 8
• NO COMILATION! - Compiles JavaScript
directly into byte code
• 20x faster than uncompiled Rhino
• Better typing
• Smaller footprint
• 100% compliant with ECMA 5.1
• Java 9 has Partial ECMA 6!

26. > jjs
jjs> var x = 10, y = 20;
jjs> x + y;
>>30
Or
> jjs example.js
Nashorn- Command Line

27. 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

28. 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

29. Nashorn Vs Rhino

30. Why you care
• Server-side JavaScript
• Leverage Existing
JavaScript Libraries
• Cross Platform scripting –
Rhino runs on Android
• Fast performance with
Nashorn
• Leverage some vNode
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?

31. Demo

32. Demo overview
• Credit card validation
• Fibonacci numbers
• Interest calculation
• Groovy Examples
https://github.com/roryp/nashorn

33. Java 9 - ECMA 6 Support!