Ruby for Java programmersUgo CeiSourcesenseu.cei@sourcesense.com

• Java programmers wishing to know how to include Ruby code in Java programs or vice-versa.•Ruby programmers wishing for the same.

Who should attend this talk

Who should NOT attend this talk• Java programmers wishing to learn more about the Ruby

programming language.•This is not a talk about the differences between Java and

Ruby.

Ugo Cei: “Ruby for Java Programmers”

•Why?•How?•Bridges• JRuby•XML-RPC•SOAP•Demos

Agenda

Ugo Cei: “Ruby for Java Programmers”

What’s in it for me?

Ugo Cei: “Ruby for Java Programmers”Ugo Cei: “Ruby for Java Programmers”

Shameless Plug: The Open Source Zone

http://oszone.org

Ugo Cei: “Ruby for Java Programmers”

Shameless Plug: The Open Source Zone

http://oszone.org

Ugo Cei: “Ruby for Java Programmers”

Shameless Plug: Evil or Not?

http://evilornot.info

Ugo Cei: “Ruby for Java Programmers”

Shameless Plug: Evil or Not?

http://evilornot.info

if /<title>(.+)<\/title>/ ... Search?

Ugo Cei: “Ruby for Java Programmers”

“The era of islands is over for most development scenarios. You don't have to make one definitive choice. Instead, you get to hog all the productivity you can for the common cases, then outsource the bottlenecks to existing packages in faster languages or build your own tiny extension when it's needed.”

David Heinemeier Hansson, Sep 13, 2006

Ugo Cei: “Ruby for Java Programmers”

How?

Ugo Cei: “Ruby for Java Programmers”

• http://arton.no-ip.info/collabo/backyard/?RubyJavaBridge•Follow the instructions in readme.txt and on the website

and it should work (even on Intel Macs).•Encapsulate you Java code in high-level methods and

classes to hide 3rd party libraries and Java idiosyncrasies from Ruby as much as possible.

RubyJavaBridge

Ugo Cei: “Ruby for Java Programmers”

•Uses ROME (https://rome.dev.java.net).

Sample Java Code

public class Fetcher { public static SyndFeed fetch(String url) throws Exception { URL feedUrl = new URL(url); FeedFetcherCache feedInfoCache = HashMapFeedInfoCache.getInstance(); FeedFetcher fetcher = new HttpURLFeedFetcher(feedInfoCache); SyndFeed feed = fetcher.retrieveFeed(feedUrl); return feed; }}

Ugo Cei: “Ruby for Java Programmers”

Client Ruby Coderequire 'rjb'

Rjb::load('.:rome-0.7.jar:rome-fetcher-0.7.jar:jdom.jar:jdom.jar', [])

fetcher = Rjb::import('Fetcher')feed = fetcher.fetch(ARGV[0])print feed.getTitle, “\n”entries = feed.getEntries.iteratorwhile entries.hasNext do entry = entries.next print "#{entry.getPublishedDate.toString} #{entry.getTitle}\n"end

•No mapping from Java iterators to Ruby loops.•No date type conversions.•No support for JavaBean properties.

Ugo Cei: “Ruby for Java Programmers”

• http://www.cmt.phys.kyushu-u.ac.jp/~M.Sakurai/cgi-bin/fw/wiki.cgi?page=YAJB•Same caveats and limitations as for RJB.

YAJB

Ugo Cei: “Ruby for Java Programmers”

Client Ruby Coderequire 'yajb/jbridge'include JavaBridge

JBRIDGE_OPTIONS = { :classpath => '.:rome-0.7.jar:rome-fetcher-0.7.jar:jdom.jar:jdom.jar'}

jimport "Fetcher"

feed = :Fetcher.jclass.fetch(ARGV[0])print feed.getTitle, "\n"entries = feed.getEntries.iteratorwhile entries.hasNext do entry = entries.next print "#{entry.getPublishedDate.toString} #{entry.getTitle}\n"end

Ugo Cei: “Ruby for Java Programmers”

Making a Simple Java Classrequire 'yajb/jbridge'require 'yajb/jlambda'

include JavaBridge

c = JClassBuilder.new("MyClass")c.add_field("private int num;")c.add_constructor("public AAA(int a) {num = a;}")c.add_method("public int square() { return num * num;}")puts "Simple class: #{c.new_instance(5).square}"

•Uses javassist: http://www.csg.is.titech.ac.jp/~chiba/javassist/index.html

Ugo Cei: “Ruby for Java Programmers”

Implementing an Interfacejimport "java.util.*"c = JClassBuilder.new("NumComp")c.add_interface("java.util.Comparator") # must be full qualified class namec.add_method(<<'JAVA')public int compare(Object o1, Object o2) do int i1 = ((Number)o1).intValue(); int i2 = ((Number)o2).intValue(); return i2-i1;endJAVAsample = [9,1,8,2,7,3,6,4,5,0,10]list = :ArrayList.jnewsample.each {|i| list.add( i )}:Collections.jclass.sort(list, c.new_instance)p "Sort:",list.toArray

Ugo Cei: “Ruby for Java Programmers”

• http://www.swig.org• Jakarta POI, nifty library for manipulating Microsoft OLE 2

Compound Document formats (Office files) uses SWIG to provide Ruby bindings.•POI compiled using gcj and Ruby bindings generated

using SWIG.• http://jakarta.apache.org/poi/poi-ruby.html

Using SWIG

Ugo Cei: “Ruby for Java Programmers”

• http://jruby.sourceforge.net/• http://jruby.codehaus.org/• JRuby is not a bridge between Java and Ruby but a full-

featured Ruby interpreter written in 100% Java.•Gives Ruby code instant access to all Java libraries.•Cannot load Ruby extensions written in C.• “Almost” Mostly able to run RubyGems and Rails.•Quick development pace.•Still slow compared to C Ruby, but quoting Charles O.

Nutter: “I think it's now very reasonable to say we could beat C Ruby performance by the end of the year.”

JRuby

Ugo Cei: “Ruby for Java Programmers”

JRuby Client Coderequire 'java'

include_class 'Fetcher'

feed = Fetcher.fetch(ARGV[0])

feed.entries.each do | entry | p "#{entry.publishedDate} #{entry.title}"end

•Can use “each” on Java collections.•Date type conversion.•Full support for JavaBean properties.

Ugo Cei: “Ruby for Java Programmers”

• demo1.rb

Calling Ruby Methods

class Demo1 def foo print 'bar' endend

IRuby runtime = Ruby.getDefaultInstance();runtime.loadFile(new File("ruby/demo1.rb"), false);RubyClass rb = runtime.getClass("Demo1");IRubyObject obj = rb.newInstance(new RubyObject[0]);obj.callMethod("foo");

•Demo1.java

Ugo Cei: “Ruby for Java Programmers”

Using the Bean Scripting Framework

BSFManager.registerScriptingEngine("ruby", "org.jruby.javasupport.bsf.JRubyEngine", new String[] { "rb" }); BSFManager manager = new BSFManager(); JLabel mylabel = new JLabel(); manager.declareBean("label", mylabel, JLabel.class); manager.exec("ruby", "(java)", 1, 1, "$label.setText(\"This is a test.\")");

•The Bean Scripting Framework, when used with JRuby, will allow you more conveniently to pass your own Java objects to your JRuby script. You can then use these objects in JRuby, and changes will affect your Java program directly.

Ugo Cei: “Ruby for Java Programmers”

•This won’t work as it conflicts with Ruby’s String and URI classes.•Solution: use a module.

Name Clashes

Ugo Cei: “Ruby for Java Programmers”

import_class ‘java.lang.String’import_class ‘java.net.URI’

module Javaimport_class ‘java.lang.String’import_class ‘java.net.URI’

end...uri = Java::URI.new(‘http://example.com/’)

•Or remap names:include_class("java.lang.Exception") {|p,n| "J" + n }

Running Ruby on Rails

Ugo Cei: “Ruby for Java Programmers”

• http://jruby.codehaus.org/The+JRuby+Tutorial+Part+2+-+Going+Camping

Running Camping

Ugo Cei: “Ruby for Java Programmers”

Using the JDBC AR Adapter

jruby $JRUBY_HOME/bin/gem install ActiveRecord-JDBC --no-ri --no-rdoc

•As of 0.2.0 works for:•MySQL•PostgreSQL•Oracle•HSQLDB•Microsoft SQL Server•DB2•Apache Derby•FireBird

Ugo Cei: “Ruby for Java Programmers”

Using the JDBC AR Adapter

adapter: jdbc driver: com.mysql.jdbc.Driver url: jdbc:mysql://localhost:3306/dbname username: admin password: secret

Ugo Cei: “Ruby for Java Programmers”

•Pro: Established technology.•Pro: No need to use bridge code or special interpreters.•Con: Separate processes => must take network latency

and failures into account.•Con: Overhead of HTTP communication, XML parsing,

marshalling...•Need to convert types to something that XML-RPC is able

to understand, i.e.strings, numbers, dates, Vectors, Hashtables and little else.

XML-RPC

Ugo Cei: “Ruby for Java Programmers”

XML-RPC Java Server

public class RPCFetcher {

public static void main(String args[]) throws Exception { WebServer server = new WebServer(8080); server.addHandler("$default", new RPCFetcher()); server.start(); }

// Continued...

•Uses Apache XML-RPC.

Ugo Cei: “Ruby for Java Programmers”

public Vector fetch(String url) throws Exception { URL feedUrl = new URL(url); FeedFetcherCache feedInfoCache = HashMapFeedInfoCache.getInstance(); FeedFetcher fetcher = new HttpURLFeedFetcher(feedInfoCache); SyndFeed feed = fetcher.retrieveFeed(feedUrl); Vector items = new Vector(); for (Iterator it = feed.getEntries().iterator() ; it.hasNext() ; ) { SyndEntry entry = (SyndEntry) it.next(); Hashtable map = new Hashtable(); map.put("link", entry.getLink()); map.put("title", entry.getTitle()); map.put("publishedDate", entry.getPublishedDate()); items.add(map); } return items; }

XML-RPC Java Server

Ugo Cei: “Ruby for Java Programmers”

XML-RPC Ruby Client

require 'xmlrpc/client'server = XMLRPC::Client.new 'localhost', '/', 8080entries = server.call('fetch', 'http://agylen.com/feed')entries.each do | entry | p "#{entry['publishedDate'].to_time} #{entry['title']}"end

Ugo Cei: “Ruby for Java Programmers”

•Complex and heavyweight, but most of the complexity is hidden by tools.•WSDL service description can be automatically generated

from server code.•Ruby’s SOAP library provides what is necessary to read

WSDL documents and create classes and methods on the fly.•Sample Java server code based on XFire samples can be

found here:http://agylen.com/2006/05/06/ruby-for-java-programmers-part-vi/.

SOAP

Ugo Cei: “Ruby for Java Programmers”

•Maps service names to service classes:

services.xml

<beans xmlns="http://xfire.codehaus.org/config/1.0"> <service> <name>BookService</name> <namespace>http://sourcesense.com/BookService</namespace> <serviceClass>com.sourcesense.xfire.demo.BookService</serviceClass> </service></beans>

Ugo Cei: “Ruby for Java Programmers”

SOAP Ruby Clientrequire 'soap/wsdlDriver'WSDL_URL = 'http://localhost:8080/services/BookService?wsdl'driver = SOAP::WSDLDriverFactory.new(WSDL_URL).create_rpc_driverbooks = driver.getBooks(nil)p books.out.book[0].titlebook = driver.findBook(:isbn => '222')p book.out.title

•The BookService#getBooks method in Java takes no arguments, but if you try to call driver.getBooks without arguments, Ruby complains about a missing argument.•XFire add this extra ‘out’ element to its generated schema.

Ugo Cei: “Ruby for Java Programmers”

Thank You!

Slides will be available athttp://agylen.com/

and athttp://www.sourcesense.com/

Ugo Cei: “Ruby for Java Programmers”