1. Rapid
Development with
Ruby/JRuby and
Rails
Lee Chuk Munn
Staff Engineer
Sun Microsystems
1

2. Why Ruby?
2

3. What is Ruby?
• Created by Yukihiro “Matz” Matsumoto
> Started around 1993, about the same time as Java
• What is a scripting language?
> No compilation unit
puts “Hello world”
> Not compiled
> Specialized syntax and data types
subject.gsub(/before/, quot;afterquot;)
> Maybe dynamic typing /duck typing
• Design to put the “fun” back into programming
3

4. Ruby Conventions
• ClassNames
• methods_names, variable_names
• visible?
• methods_with_side_effects!
• @instance_variable
• @@class_variable
• $global_variable
• A_CONSTANT, AnotherConstant
• MyClass.class_method – doc only
• MyClass#instance_method – doc only
4

5. A Typical Ruby Class
class Song Properties
@@plays = 0
attr_accessor :name, :artist, :duration
def initialize(d, a, d)
@name = n; @artist = a; @duration = d
end
Constructor public
def duration_in_minutes
@duration / 60
No return end Virtual properties
def duration_in_minutes=(v)
@duration = (v * 60)
end Interpolated values
def play
@@plays += 1
puts quot;#{@name} plays #{@@plays}quot;
@@plays
end
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end

6. Sample Execution
s = Song.new(“Cavatina”, “John Williams”, 200)
puts(“duration: #{s.duration}”)
puts “in mins: #{s.duration_in_minutes}”
s.duration_in_minutes = 4
puts “in mins: #{s.duration}”
s.play
6

7. Symbols
• :a_name is symbol, think identities
> Refer to the name a_name, not the value that a_name
may potentially hold
• Typically used in maps, property declaration,
method names, any place you need a name/symbol
:foo foo
Symbol table
foo
Memory location
bar
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8. Example Use of Symbols
attr_accessor :color, :age, :name Attribute
protected :deposit, :withdrawl Access modifiers
color = {
:red => 0xf00, Maps
:green => 0x0f0,
:blue => 0x00f As keyword parameters
}
add_column :plugins, :price, :decimal,
:precision => 8, :scale => 2, :default => 0
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9. Everything Returns a Value
• Returned not required
def duration_in_minutes
@duration / 60
end
• Statements can be used as expressions
gt = if (x > y) true else false
• Even defining a method has a return value
> Returns nil
9

10. Everything Is An Object
• 'Primitives' are objects
> -1.abs
• nil is an object
> nil.methods
• Classes are objects
> Song.new – invoking the new method on 'Song' object
> Create instances of themselves
• Code blocks are objects
> They can be pass around, even as parameters
> Blocks can be closure
10

11. Customization with Closure
class ColorButton
attr_accessor :label, :r, :g, :b
def initialize(l)
label = 1
r = 0x0f
g = 0x0f
b = 0x0f
if block_given?
yield self
end
end b = ColorButton(“Press me”) do |button|
button.r = 0xff
# more stuff
...
end 11

12. Common Uses of Closures
• Iteration
[1,2,3].each {|i| puts i }
• Resource management
File.new(quot;/etc/hostsquot;, quot;rquot;).each {|e| puts e }
• Callbacks
widget.on_button_press { puts quot;Button Pressquot; }
• Initialization
a = Array.new(5) {|i| i * i }
From http://onestepback.org/articles/10things/item3.html 12

13. Almost Everything is a Method Call
• In lots of cases, invoking method without knowing it
array[i] = 0 – invoking the [] method
1 + 2 + 3 – 1.+(2.+(3))
str.length
• Methods can be invoked with or without parenthesis
> Most developers chose the latter
> Code looks more natural especially if you are doing DSL
• Methods can be overridden
> Get operator overloading for free
13

14. Every Method Call is a Message
• obj.method(param) means having a method on the
object in Java
• In Ruby, this means sending a message to the
object
obj.send(:method, param)
is to send a '+' message with one value
1+2+3
1.send(:+, 2.send(:+, 3))
• Use respond_to? to find out if an object knows how
to handle a message
1.respond_to? :succ => true
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15. So What Is the Big Deal?
public VCR
def initialize varag
@messages = []
end
def method_missing(method, *args, &block)
@messages << [method, args, block]
end Push triplet onto array
def play_back_to(obj)
@messages.each do |method, args, block|
obj.send(method, *args, &block)
end
end
end
From http://onestepback.org/articles/10things/page017.html 15

16. Example of Macro at the Language Level
vcr = VCR.new
vcr.sub!(/Java/) { |match| match.reverse }
vcr.upcase! Capture a group of
vcr[11,5] = quot;Universequot; operations. Reapply
vcr << quot;!quot; these on a separate
object
string = quot;Hello Java Worldquot;
puts string
vcr.play_back_to(string)
puts string # => quot;Hello AVAJ Universequot;
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17. Duck Typing Instead of Interfaces
• Familiar with the idea of using interface to enforce
contracts
> An object can only be considered a thread if it
implements Runnable
• If an object can behave like a thread, then should
be considered as a thread
> Runnable is irrelevant if it has run()
> If it walks like a duck, talks like a duck, then we can treat
it as a duck
d = DuckLikeObject.new
puts d.quack if d.responds_to :quack
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18. Reuse – Inheritance
• Supports inheritance
class KaraokeSong < Song
...
def to_s
super + “[#{@lyrics}]”
end
18

19. Reuse - Mixins
• Multiple inheritance like mechanism call mixins
defined by modules
> A namespace
> Can have methods
> But cannot be instantiated
• Becomes part of a class when included a module is
included in a class
> The reverse is also possible by extending the module
with an object
19

20. Mixin Example
module Stringify class MyNumber
def stringify include Stringify
if @value == 1 def initialize(value)
quot;Onequot; @value = value
elsif @value == 2 end
quot;Twoquot; ...
elsif @value == 3
quot;Threequot;
end
end
end
Stringify example http://www.juixe.com/techknow/index.php/2006/06/15/mixins-in-ruby/ 20

21. Reuse – Modifying Existing Class
• Methods can be added to a class at any time
> Applies to built in classes
• Can be frozen
class String
def rot13
self.tr(quot;A-Ma-mN-Zn-zquot;,quot;N-Zn-zA-Ma-mquot;)
end
end
“hello world”.rot13 #=> uryyb jbeyq
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22. Extremely Flexible and Dynamic
• One of the hallmarks of scripting languages
• Metaprogramming – programs that write or
manipulate themselves
• Some of the stuff you can do
> Trap missing methods and add them if you so desire
> Kernel definition hooks eg. Adding a method
> Create code and execute them on the fly
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23. Example of Ruby's Malleability
class Foo
def method_missing(name, *args)
if args[0].is_a?(Proc)
self.class.instance_eval do
define_method(name.to_s.chomp(quot;=quot;), args[0])
end
else
super
end
end f = Foo.new
end f.greet = lambda {|t| quot;Hello #{t}!quot;}
f.greet quot;Hello SunTech Daysquot;
Adapted from http://tech.rufy.com/2006/08/dynamically-add-methods-to-classes.html
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24. DSLs with Ruby
• DSL is a language designed for a specific domain
> Captures jargon in language
• Ruby's DSL is internal (Fowler)
> Morph language into DSL
> Java is external and/or API based
• Killer features for DSL with Ruby
> Paranthesis-less method invocation
> Closures
> Malleable and dynamc engine
> Variable argument list
> Symbols
24

25. DSL Example
PBJ Sandwich recipe quot;PBJ Sandwichquot;
ingredients: ingredients :bread 2.slice
- two slices of bread ingredients :peanut_butter 1.spoon
- one tablespoon of peanut butter ingredients :jam 1.teaspoon
- one teaspoon of jam instructions do
step 1 “spread peanut butter”
instructions: step 2 “spread jam...”
- spread peanut butter on bread step 3 “place other slice...”
- spread jam on top of peanut butter end
- place other slice of bread on top
servings 1
prep_time 2.minutes
servings: 1
prep time: 2 minutes
Adapted from http://weblog.jamisbuck.org/2006/4/20/writing-domain-specific-languages
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26. This is great, but...
• Ruby language is different from Java
• Ruby platform is different from Java
• How can Java developers benefit?
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27. JRuby
• Implementation of Ruby written in Java
• Compatible with Ruby 1.8.6
• Enables use of Java code in Ruby
• Easier deployment
• More libraries
• More platforms
• Less “political” resistence
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28. FreeTTS Example
• In Java
VoiceManager vm = VoiceManager.getInstance();
Voice voice = vm.getVoice(quot;kevin16quot;);
voice.allocate();
voice.speak(jTextArea1.getText());
voice.deallocate();
• In Ruby
require 'java'
vm = com.sun.speech.freetts.VoiceManager.getInstance()
voice = vm.getVoice(quot;kevin16quot;)
voice.allocate()
voice.speak(quot;Calling Java code from Rubyquot;)
voice.deallocate()
• JRuby engine available through JSR-223 in JavaSE 6 28

29. Rapid
Development with
Ruby/JRuby and
Rails
Lee Chuk Munn
Staff Engineer
Sun Microsystems
29

30. 3. Inserting New or Existing Slides
● To add a new slide to your presentation, select
Insert>Slide. You can also duplicate slides in the
Slide Sorter using copy and paste.
● To add a slide(s) from another presentation,
copy and paste from one file to the other in
the Slide Sorter.
● To insert an entire presentation, select Insert>File.
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31. Template – Text Slide
with Two Line Title and Subtitle
This is a Subtitle with Initial Caps Each Major Word
• To insert a Subtitle on other slides, copy and paste
the Subtitle text block
• On a slide with a two line Title and Subtitle (as
shown here) move the bullet text block down to
make room for the Subtitle. You can also duplicate
this slide and replace the content.
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32. GlassFish V2
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45. Title Here
Lee Chuk Munn
Staff Engineer
Sun Microsystems
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