Ugo Cei Presentation

Ruby for Java
programmers
Ugo Cei
Sourcesense
u.cei@sourcesense.com

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

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”

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


What’s in it for me?


Shameless Plug: The Open Source Zone

http://oszone.org

Shameless Plug: Evil or Not?

http://evilornot.info

Shameless Plug: Evil or Not?

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

http://evilornot.info

“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

How?


RubyJavaBridge
• 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.


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

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;
}
}


Client Ruby Code
require '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.iterator
while entries.hasNext do
entry = entries.next
print quot;#{entry.getPublishedDate.toString} #{entry.getTitle}nquot;
end
• No mapping from Java iterators to Ruby loops.
• No date type conversions.
• No support for JavaBean properties.


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


Client Ruby Code
require 'yajb/jbridge'
include JavaBridge

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

jimport quot;Fetcherquot;

feed = :Fetcher.jclass.fetch(ARGV[0])
print feed.getTitle, quot;nquot;
entries = feed.getEntries.iterator
while entries.hasNext do
entry = entries.next
print quot;#{entry.getPublishedDate.toString} #{entry.getTitle}nquot;
end


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

include JavaBridge

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

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


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


Using SWIG
• 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


JRuby
• 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 Client Code
require 'java'

include_class 'Fetcher'

feed = Fetcher.fetch(ARGV[0])

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

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


Calling Ruby Methods
• demo1.rb

class Demo1
def foo
print 'bar'
end
end

• Demo1.java
IRuby runtime = Ruby.getDefaultInstance();
runtime.loadFile(new File(quot;ruby/demo1.rbquot;), false);
RubyClass rb = runtime.getClass(quot;Demo1quot;);
IRubyObject obj = rb.newInstance(new RubyObject[0]);
obj.callMethod(quot;fooquot;);


Using the Bean Scripting Framework
• 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.

BSFManager.registerScriptingEngine(quot;rubyquot;,
quot;org.jruby.javasupport.bsf.JRubyEnginequot;, new String[] { quot;rbquot; });
BSFManager manager = new BSFManager();
JLabel mylabel = new JLabel();
manager.declareBean(quot;labelquot;, mylabel, JLabel.class);
manager.exec(quot;rubyquot;, quot;(java)quot;, 1, 1, quot;$label.setText(quot;This is a test.quot;)quot;);


Name Clashes
import_class ‘java.lang.String’
import_class ‘java.net.URI’
• This won’t work as it conflicts with Ruby’s String and URI
classes.
• Solution: use a module.
module Java
import_class ‘java.lang.String’
import_class ‘java.net.URI’
end
...
uri = Java::URI.new(‘http://example.com/’)

• Or remap names:
include_class(quot;java.lang.Exceptionquot;) {|p,n| quot;Jquot; + n }


Running Ruby on Rails


Running Camping

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


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


Using the JDBC AR Adapter

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


XML-RPC
• 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 Java Server
• Uses Apache XML-RPC.

public class RPCFetcher {

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

// Continued...


XML-RPC Java Server
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(quot;linkquot;, entry.getLink());
map.put(quot;titlequot;, entry.getTitle());
map.put(quot;publishedDatequot;, entry.getPublishedDate());
items.add(map);
}
return items;
}


XML-RPC Ruby Client

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


SOAP
• 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/.


services.xml
• Maps service names to service classes:

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


SOAP Ruby Client
require 'soap/wsdlDriver'
WSDL_URL = 'http://localhost:8080/services/BookService?wsdl'
driver = SOAP::WSDLDriverFactory.new(WSDL_URL).create_rpc_driver
books = driver.getBooks(nil)
p books.out.book[0].title
book = 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.


Thank You!

Slides will be available at
http://agylen.com/
and at
http://www.sourcesense.com/


Ugo Cei Presentation

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