A (Quick) Introduction
to JRuby
Frederic Jean
fred@fredjean.net

Hello JRuby

Develop, Deploy, Build, Test, Monitor
Configuration
DSLs
Glue, Wiring
External System Integration
Dynamic Layer
Application Code
Stable Layer
Java, Statically typed
Legacy libraries

Ruby

Ruby is...
• Dynamically Typed
• Strongly Typed
• Everything is An Object

(Almost) Everything is
an Object

Ruby Literals
# Strings
\"This is a String\"
'This is also a String'
%{So is this}
# Numbers
1, 0xa2, 0644, 3.14, 2.2e10
# Arrays and Hashes
['John', 'Henry', 'Mark']
{ :hello => \"bonjour\", :bye => \"au revoir\"}
# Regular Expressions
\"Mary had a little lamb\" =~ /little/
\"The London Bridge\" =~ %r{london}i
# Ranges
(1..100) # inclusive
(1...100) # exclusive

Symbols
:symbol
• String-like construct
• Only one copy in memory

Blocks
['John', 'Henry', 'Mark'].each { |name| puts \"#{name}\"}
File.open(\"/tmp/password.txt\") do |input|
text = input.read
end

Ruby Classes
class Person
attr_accessor :name, :title
end
p = Person.new

Open Classes
class Fixnum
def odd?
self % 2 == 1
end
def even?
self % 2 == 0
end
end
http://localhost:4567/code/fixnum.rb

Mixins
module Parity
def even?
self % 2 == 0
end
def odd?
self % 2 == 1
end
end
http://localhost:4567/code/parity.rb

Mixins
class Person
include Enumerable
attr_accessor :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
def <=>(other)
if self.last_name == other.last_name
self.first_name <=> other.first_name
else
self.last_name <=> other.last_name
end
end
def to_s
\"#{first_name} #{last_name}\"
end
end
http://localhost:4567/code/sorting.rb

JRuby

JRuby
• Ruby Implementation on the JVM
• Compatible with Ruby 1.8.6
• Native Multithreading
• Full Access to Java Libraries

JRuby Hello World
java.lang.System.out.println \"Hello JRuby!\"
http://localhost:4567/code/jruby_hello.rb

Java Integration
require 'java'

JI: Ruby-like Methods
Java Ruby
Locale.US Locale::US
System.currentTimeMillis() System.current_time_millis
locale.getLanguage() locale.language
date.getTime() date.time
date.setTime(10) date.time = 10
file.isDirectory() file.directory?

JI: Java Extensions
h = java.util.HashMap.new
h[\"key\"] = \"value\"
h[\"key\"]
# => \"value\"
h.get(\"key\")
# => \"value\"
h.each {|k,v| puts k + ' => ' + v}
# key => value
h.to_a
# => [[\"key\", \"value\"]]
http://localhost:4567/code/ji/extensions.rb

JI: Java Extensions
module java::util::Map
include Enumerable
def each(&block)
entrySet.each { |pair| block.call([pair.key, pair.value]) }
end
def [](key)
get(key)
end
def []=(key,val)
put(key,val)
val
end
end

JI: Open Java Classes
class Java::JavaLang::Integer
def even?
int_value % 2 == 0
end
def odd?
int_value % 2 == 1
end
end
http://localhost:4567/code/ji/integer.rb

JI: Interface Conversion
package java.util.concurrent;
public class Executors {
// ...
public static Callable callable(Runnable r) {
// ...
}
}

JI: Interface Conversion
class SimpleRubyObject
def run
puts \"hi\"
end
end
callable = Executors.callable(SimpleRubyObject.new)
callable.call
http://localhost:4567/code/ji/if_conversion.rb

JI: Closure Conversion
callable = Executors.callable { puts \"hi\" }
callable.call
http://localhost:4567/code/ji/closure_conversion.rb

Develop, Deploy, Build, Test, Monitor
Configuration
DSLs
Glue, Wiring
External System Integration
Dynamic Layer
Application Code
Stable Layer
Java, Statically typed
Legacy libraries

Usage
• Runtime
• Wrapper around Java Code
• Calling From Java
• Utilities

JRuby as a Runtime

JRuby on Rails
• Wrap Rails app into a war file
• Direct support in Glassfish v3 Prelude
• http://kenai.com
• http://mediacast.sun.com

webmate
require 'rubygems'
require 'sinatra'
get '/*' do
file, line = request.path_info.split(/:/)
local_file = File.join(Dir.pwd, file)
if (File.exists?(local_file))
redirect \"txmt://open/?url=file://#{local_file}&line=#{line}\"
else
not_found
end
end
http://localhost:4567/code/webmate.rb

Wrapping Java Code

Swing Applications
frame = JFrame.new(\"Hello Swing\")
• Reduce verbosity
• Simplify event handlers
http://localhost:4567/code/swing.rb

RSpec Testing Java
describe \"An empty\", HashMap do
before :each do
@hash_map = HashMap.new
end
it \"should be able to add an entry to it\" do
@hash_map.put \"foo\", \"bar\"
@hash_map.get(\"foo\").should == \"bar\"
end
end
JTestr Provides Ant and Maven integration
http://jtestr.codehaus.org
http://localhost:4567/code/hashmap_spec.rb

Utilities

Develop, Deploy, Build, Test, Monitor
Configuration
DSLs
Glue, Wiring
External System Integration
Dynamic Layer
Application Code
Stable Layer
Java, Statically typed
Legacy libraries

Build Utilities
• Rake
• Raven
• Buildr

Conclusion

Resources
• http://jruby.org
• http://wiki.jruby.org
• http://jruby.kenai.com
• http://jtester.codehaus.org
• http://raven.rubyforge.org
• http://buildr.apache.org