Presented at JAX London 2013 Java is not the only language! The JVM is a wonderful common runtime for a wide variety of languages. By using the right language for each task, you can deliver higher quality applications in less time.

1. Ben Summers | ONEIS
Real-world polyglot programming
on the JVM

2. Real-world polyglot
programming on the JVM
Be n Su m me r s
Te c hnic a l d i re ctor, ON EIS
@b e nsu mm ers

3. This is nothing new.

6. Actual language usage
• Primary programming language
• Con!guration + build system
• Presentation
• Miscellaneous scripting

7. Polyglot programming
is a formalisation.

8. A polyglot application
Ruby
40%
Java
20%
JavaScript
20%
HTML, CSS, etc
18%
C++
1%
Python
1%

9. Table of contents
• How I became a polyglot programmer
• The case for polyglot programming
• Languages, JVM and polyglot apps
• Impedance mismatch
• Glue code
• Language boundaries
• Getting started

10. An accidental polyglot
flickr: darynbarry

12. ONEIS architecture
JavaScript
Ruby
Java
Java
Jetty
Internet
JVM
Worker Worker Worker Worker
JVM
JVM
JVM
JVM
Sandboxed
JavaScript
plugins

13. The case for polyglot
flickr: dm-set

14. Languages are not equal
• Expressiveness
• Performance
• Readability
• Style
• Static
• Dynamic
• Functional
• WTF

15. The case for polyglot
• “Real artists ship”
• You’re doing it already
• Formalisation and extension

16. Ola Bini’s pyramid
http://olabini.com/blog/2008/06/fractal-programming/

17. Java
JVM
Rub
y
San
dbo
Java
xed
Scr
plug ipt
ins
Ola Bini’s pyramid
Java
Ja
vaS
c
ript

18. Why the JVM?
• Great runtime
• Portability
• Common underlying VM for lots of
languages
• Interoperability
• Java library for everything

19. Side note:
Don’t forget the CLR
• Good stu" from Microsoft
• Great runtime
• DLR
• APIs
• Di"erent culture
• Trap?

20. Side note:
Don’t forget IPC
• Go old school
• Separate processes
• Common protocol over sockets and
pipes
• Thrift, Google Protocol Bu"ers, Avro
• or text over HTTP: XML, JSON, etc

21. Languages and the JVM
flickr: munksynz

22. What’s the best language?
• No such thing as the “best” language
• Use the best language for solving
your problems
• Polyglot is about avoiding compromises

23. Language choice
• Don’t use two closely related languages
• Don’t forget the standard library
• And some have special features
eg. concurrency libraries

24. Pick one from each column
Static
Dynamic
Scripting / DSLs
Java
Ruby
JavaScript
Scala
Groovy
Ruby
Clojure
Groovy
Jython

25. Aims
• Work in harmony
• Choose most appropriate language for
each task
• Choose carefully as choices are hard to
undo

26. Memory usage
• Multiple runtimes
• Multiple standard libraries
• Cloud is memory constrained

27. Impedance mismatch
flickr: h080

28. Impedance mismatch
• Type systems
• Your languages won’t agree on the
simplest things:
• Strings, Numbers, Dates, Arrays, null

29. Strings
• Java: UTF-16 (ish) strings
• JavaScript: implementation dependent
• Browsers: UCS-16 usually
• JVM: Whatever Java does + optimisations
• Ruby
• bytes (1.8), or bytes+encoding (1.9)
• JVM originated languages: Java Strings

30. Numbers
• Java: primitives, java.lang.Number, etc
• JavaScript: doubles only.
Plus odd Number object.
• Ruby:
• ints (always Fixnum) with silent promotion to
Bignum
• doubles, Rational

31. null
• Java: null
• Ruby: nil
• JVM languages: null
• JavaScript: null and undefined

32. Javascript’s
null and undefined
var o = {item: null};
if(o.item === undefined) {
console.log("0");
}
if(o.noSuchItem === undefined) {
console.log("1");
}
OUTPUT
1

33. Javascript’s
null and undefined
var o = {item: null};
if(o.item === undefined) {
console.log("0");
}
if(o.noSuchItem === undefined) {
console.log("1");
}
var undefined = 42;
if(o.noSuchItem === undefined) {
console.log("2");
}
OUTPUT
1

34. JavaScript Top Tip
Use JSHint in
your tests
(but not JSLint)

35. Strings, numbers, dates...
• Impedance mismatch means you have
to think about the boundaries
• Use Groovy?

36. Glue code
flickr: samcatchesides

37. Glue code
• Work around impedance mismatch
• Java: The new assembly language
• Rule enforcement & security
• Cheat until your pro!ler says it’s slow
• Serialise/deserialise to common format,
eg JSON

38. undefined is not null
JAVA
public class Host
extends ScriptableObject {
public String
jsFunction_f(String x)
{
System.out.println(
"x = " + x
);
}
}

39. undefined is not null
JAVA
public class Host
extends ScriptableObject {
public String
jsFunction_f(String x)
{
System.out.println(
"x = " + x
);
}
}
JAVASCRIPT
var h = new Host();
h.f("Hello");
h.f(2);
h.f(null);
h.f(undefined);

40. undefined is not null
JAVA
public class Host
extends ScriptableObject {
public String VALUES OF X
jsFunction_f(String x)
{
System.out.println(
"x = " + x"Hello"
);
"2"
}
null
}
"undefined"
JAVASCRIPT
var h = new Host();
h.f("Hello");
h.f(2);
h.f(null);
h.f(undefined);

41. null and undefined are 0
JAVA
public void jsFunction_each(
Integer desc, boolean hasDesc,
Integer qual, boolean hasQual)
JAVASCRIPT
Store.prototype.each = function(desc, qual) {
return this.$store.each(
desc, (desc !== null && desc !== undefined),
qual, (qual !== null && qual !== undefined)
);
};

42. Conversions
public static Date tryConvertJsDate(Object jsObject)
{
if(jsObject == null) { return null;}
if(nativeDateClass == null) {
try { nativeDateClass =
Class.forName("org.mozilla.javascript.NativeDate"); }
catch(ClassNotFoundException e) { /* ... */ }
}
if(nativeDateClass.isInstance(jsObject)) {
Object d = Context.jsToJava(jsObject, Date.class);
if(d != null && d instanceof Date) {
return (Date)d;
}
}
}
return null;

43. Calling Java is easy
• Don’t let JavaScript put you o"
• Calling Java APIs from any other
language is easy

44. Create a JPEG with Java
import
import
import
import
java.awt.image.BufferedImage;
java.awt.Graphics2D;
javax.imageio.ImageIO;
java.io.File;
public class MakeImage
{
public BufferedImage makeImage(int w, int h) {
BufferedImage image = new BufferedImage(w, h, TYPE_INT_RGB);
Graphics2D graphics = image.createGraphics();
graphics.drawString("Hello world", w/2, h/2);
graphics.dispose();
return image;
}
}
public static void main(String args[]) throws Exception {
BufferedImage img = (new MakeImage()).makeImage(200, 400);
ImageIO.write(img, "jpeg", new File("test.jpeg"));
}

45. Create a JPEG with JRuby
require 'java'
class MakeImage
java_import java.awt.image.BufferedImage;
java_import java.awt.Graphics2D;
def make_image(w, h)
image = BufferedImage.new(w, h, BufferedImage::TYPE_INT_RGB)
graphics = image.create_graphics
graphics.draw_string("Hello world", w/2, h/2)
graphics.dispose
image
end
end
java_import javax.imageio.ImageIO;
java_import java.io.File;
img = MakeImage.new.make_image(200, 400)
ImageIO.write(img, "jpeg", File.new("test.jpeg"))

46. The artwork

47. Divided by a
common language
• JRuby: Transparent bridging
• JavaScript: Host objects + bridging
• Groovy: Java is subset of Groovy
• Scala: Write Java with Scala syntax

48. JSR-223
• Java Scripting API
• Common API for scripting languages on
the JVM
• Scripting “engines” available for many
languages, variable quality
• Su"ers from impedance mismatch itself
• Functions may return unexpected types

49. Language boundaries
flickr: dinomite

50. Ola Bini’s pyramid
http://olabini.com/blog/2008/06/fractal-programming/

51. Boundaries
• Which language for each module?
• Clear boundaries, not a free-for-all.
• Well de!ned (and documented)
interfaces

52. Java to Ruby
public interface Framework
{
void startApplication();
void startBackgroundTasks();
void stopApplication();
}
Response handleFromJava(
HttpServletRequest request,
Application app,
byte[] body,
boolean isRequestSSL);

53. Ruby implementation
class Framework
def start_application
# ...
end
def handle_from_java(
servlet_request, application, body, is_ssl)
# magic goes here
end
end

54. JavaScript to Ruby
(via Java)
public interface AppWorkUnit
{
public int id();
public
public
public
public
}
Integer actionableById();
void setActionableById(Integer id);
String jsGetDataRaw();
void jsSetDataRaw(String data);
public boolean save();
public void destroy();

55. Security
• Trust models
• Sandboxing interpreters
vs sandboxed interpreters

56. Building the team
flickr: AaronLMGoodwin

57. Hiring polyglots

58. Hiring polyglots
developers

59. Hiring polyglots
developers
• Find people who can write code,
not people who can write Java.
• Test to see if programming is instinctive,
not syntax and trivia.
• Look for people who continuously learn,
not those who have learnt.

60. Finding a polyglot job
• Smaller companies, or smaller teams
within large companies
• Early stage projects, not maintenance or
enhancements
• Talk to really good recruiters
• Networking!

61. Getting started
flickr: holyhoses

62. The Enterprise
• It’s just Java the JVM
• Implement a servlet
• Use tools like Warbler
• TorqueBox
• New job outside the Enterprise

63. Starting points
• Use JRuby to try out an API
• Use Ruby testing libraries to test your
Java
• Use Groovy to a make business rules
DSL
• Write a layer of a small project in a
dynamic language

64. Polyglot programming:
Not new,
but very e!ective.

65. Questions?
Be n Su m me r s
Te c hnic a l d i re ctor, ON EIS
@b e nsu mm ers
http://bens.me.u k
onei s .co.uk / jo b s