#will output bytecode foo/bar/test.class
jrubyc foo/bar/test.rb 

java -cp .:/path/to/jruby.jar foo.bar.test

#JIT compile source code
jruby -S foo/bar/test.rb

jruby --properties

export JRUBY_OPTS="-X<property>=<value>"

jruby -J-Djruby.<property>=<value> -S foo.rb

<property>=<value>

require 'java'

require 'path/to/mycode.jar'

$CLASSPATH << "target/classes"

Java: org.foo.department.Widget
Ruby: Java::OrgFooDepartment::Widget

 java_import java.util.ArrayList
 list = ArrayList.new

module MyApp
 include_package 'org.apache.logging.log4j'
 Logger = LogManager.getLogger('MyApp')
end

  java.lang.System.currentTimeMillis
  java.lang.System.current_time_millis

  x.getSomething            becomes   x.something
  x.setSomething(newValue)  becomes   x.something = new_value
  x.isSomething             becomes   x.something?

java_class
java_kind_of? #the same as instanceof operator
java_object
java_send #based on reflection
java_method
java_alias

button = new javax.swing.JButton("Press me!");

button.addActionListener(new ActionListener(){ 
  public void actionPerformed(ActionEvent e){ 
    ((javax.swing.JButton) e.getSource()).setText("You did it!");
  } 
});

button = javax.swing.JButton.new "Press me!"

button.add_action_listener do |event|
 event.source.text = "You did it!"
end

 begin
   java.lang.Integer.parse_int("asdf")
 rescue java.lang.NumberFormatException => e
   puts "Failed to parse integer: #{e.message}"
   puts e.print_stack_trace
 end

raise java.lang.IllegalArgumentException.new("Bad param")

ni = java.net.NetworkInterface.networkInterfaces
puts ni.class.ancestors

#=> [#<Class:01x7e666f>, Java::JavaUtil::Enumeration, Enumerable, 
#        Java::JavaLang::Object, ConcreteJavaProxy, JavaProxy,
#         JavaProxyMethods, Object, Java, Kernel]

java.net.NetworkInterface.networkInterfaces.each {|i| puts i }

# Equivalent to Java's bytes = new byte[1024];  
bytes = Java::byte[1024].new 
list = java.util.ArrayList[1024].new
map = java.util.HashMap[1024].new

  [1,2,3].to_java
  ["a","b","c"].to_java(:string)
  [1, 2, 3.5].to_java Java::double

  java_arry.to_a
  java_map.to_hash
  java_set.to_set

  bytes = 'a string'.to_java_bytes
  string = String.from_java_bytes bytes

  # works for InputStreams, OutputStreams, and NIO Channels
  io = java_input_stream.to_io 
  # also to_outputstream and to_channel
  stream = io.to_inputstream

 # Get the the three-integer constructor for this class
 construct = JavaClass.java_class.constructor(Java::int, Java::int, Java::int)
 object = construct.new_instance(0xa4, 0x00, 0x00)

 java_import java.util.ArrayList

 list = ArrayList.new
 list.java_send :add, [Java::int, java.lang.Object], 0, 'foo'

 add = list.java_method :add, [Java::int, java.lang.Object]
 add.call(0, 'foo')

 class ArrayList
   java_alias :simple_add, :add, [Java::int, java.lang.Object]
 end

def bench_mark(n)
  start = Time.now
  1.upto(n).map do |n|
    Thread.new { sleep(0.5) }
  end.each(&:join)
  Time.now - start
end

def bench_mark(n)
  start = Time.now
  1.upto(n).map do |n|
    Thread.new { fib(32) }
  end.each(&:join)
  Time.now - start
end

def fib(n)
  n < 2 ? n : fib(n-1) + fib(n-2)
end

 obj.synchronized do
   obj.wait 1000
 end

jruby -J-Xmn512m -J-Xms2048m -J-Xmx2048m -J-server

#Gemfile
gem 'activerecord-jdbcmysql-adapter'# for mysql
gem 'activerecord-jdbcsqlite3-adapter'# for sqlite
gem 'activerecord-jdbcpostgresql-adapter'# for postgres

#Jarfile
# Custom repos which are not Maven Central
repository :aicorporation, "LOCAL_REPO_URL"

jar 'com.fasterxml.jackson.module:jackson-module-mrbean', '2.4.3'

jar 'com.fasterxml.jackson.core:jackson-core', '2.4.3'

jar 'com.fasterxml.jackson.core:jackson-databind', '2.4.3'

#in Gemfile
platform :jruby do
  gem 'activerecord-jdbcpostgresql-adapter', '~> 1.3.7'
end

platform :ruby do
  gem 'pg', '~> 0.17.1'
end

# add the --debug flag to your ruby/jruby command
  def index
    binding.pry
    @posts = Post.all
  end

package cz.wildweb.example;

import static cz.wildweb.api.Wildweb.*;

public class Main {

    public static void main(String[] args) {
        get("/", (req, res) -> { res.close("Welcome"); });
        startServer(8080);
    }

}

jruby -S gem install warbler

# generate config file in config/warble.rb
warble config

jruby -S rake assets:precompile

# at root of rails project
warble 

// in web.xml file
<listener>
  <listener-class>org.jruby.rack.rails.RailsServletContextListener</listener-class>
</listener>

  # only these four features supported atm  
  config.features = %w(gemjar executable runnable compiled)

  # Application directories to be included in the webapp.
  config.dirs = %w(app config db lib log script vendor tmp)

  # Public ROOT mapping
  config.public.root = ''

  # Value of RAILS_ENV for the webapp -- default as shown below
  config.webxml.rails.env = ENV['RAILS_ENV'] || 'production'

  # Control the pool of Rails runtimes.
  config.webxml.jruby.min.runtimes = 2
  config.webxml.jruby.max.runtimes = 4

jruby -S gem install jruby-openssl

#in Jarfile
jar 'org.bouncycastle:bcprov-jdk15on', '1.47'