Ruby for Java Programmers, Part V

27 02 2006

If you’ve been following the previous articles in this series (Part I, Part II, Part III and Part IV) but are not yet satisfied with the range of solutions I presented for calling Ruby code from Java, here’s another one for you.

This one involves running your Java code as a separate process and interacting with it using some form of Web service (XML-RPC, SOAP or a RESTful service). We’ll use XML-RPC for this sample, mainly because it’s very easy to set up and use. You’ll need Apache XML-RPC version 2 to make the code run. Here’s the java code:

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

    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);
            Hashtable map = new Hashtable();
            map.put("link", entry.getLink());
            map.put("title", entry.getTitle());
            map.put("publishedDate", entry.getPublishedDate());
        return items;

Compared to the previous samples, there’s not much else you need to do, besides creating an instance of WebServer to handle incoming HTTP requests and dispatch them to the appropriate method. However, you need to convert your Java types to something that XML-RPC is able to understand, i.e. strings, numbers, dates, Vectors, Hashtables and little else.

The Ruby client code is much simpler:

require 'xmlrpc/client'
server = 'localhost', '/', 8080
entries ='fetch', '')
entries.each do | entry |
  p "#{entry['publishedDate'].to_time} #{entry['title']}"

Possible drawbacks of this technique are the necessity of having a separate process running and the overhead of HTTP communication and XML-RPC protocol encoding and decoding.

Thanks to Nick Stuart and Erik Hatcher for laying down the basics.




2 responses

6 05 2006
Agylen » Ruby for Java Programmers, Part VI

[…] In the previous episode from this series, I showed you how to use XML-RPC to call Java code from Ruby over the network. In this article, we will do the same, but using SOAP instead of XML-RPC. One advantage of SOAP over XML-RPC is the fact that SOAP endpoints can be described using WSDL and, by using Ruby’s extensibility, new methods can be created on the fly to mirror the methods declared in the WSDL, therefore giving us a lot of nice loose coupling. […]

25 01 2007

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