RSS : Java Glossary

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RSS

RSS

technique of broadcasting a newsfeed from a website summarising changes. RDF (Resource Development Framework). Nature Magazine sends its daily updates that way. They provide headlines, summaries and links for all the new web content and their own and associated sites. The feed is in RDF/XML.

menu
Introduction	Advantages
RSS-2	Setting Up a RSS Feed
RDF	Aggregators
Feedburner	Books
Atom 3	Links
Viewing Feeds

Introduction

You don’t need special server software to serve feeds. You create XML (extensible Markup Language) files and upload them. The only thing you have to your server in ensure it serves XML with the correct MIME (Multipurpose Internet Mail Extensions) type — application/xml. or text/xml You can check if your server is already configured by uploading an XML file and checking it with MimeCheck. The reader handles the cleverness of polling and downloading merging what it has with recent postings.

There are seven RDF variants, Atom and RSS. You probably want to use RSS version 2.0, or support multiple formats including Atom 3. Atom was designed after RSS and is considered cleaner.

Websites called aggregators spider the various feeds and keep a central database of them and redistribute the information in various ways.

RSS-2

The items are stored in reverse chronological order. Even if you stop posting old items, your viewers may optionally retain copies of them. Normally you would just post a week through a month’s worth of the most recent items, then discard them. People who want to keep old ones, can keep their own copies. You don’t need to serve an archive.

Most of the fields are pretty obvious. You can learn details about the many optional fields.

Unlike ordinary XML, there is no DTD (Document Type Definition).

The TTL (Time To Live) in minutes, how long a copy of your feed could be cached before it should be considered stale.

The image is logo for your feed, by default 88 × 30 pixels.

The optional GUID (Globally Unique Identifier) (not guide) is a string that uniquely identifies the item. When present, software reading your feed can use this unique string to determine if an item is new. In my HTML (Hypertext Markup Language) Static macros implementatin, I created it by computing a MD5 digest of the website, feed, link, title and publish date giving 16 bytes (256 bits) which I display display as a 32-digit hex number. You want a globally unique id, not just unique within the file, unique within the feed over time or unique over your site:

<!-- example of a hash-style guid -->
<guid isPermaLink="false">2000220155</guid>

then the id is just a meaningless hash.

But

then the link is also a URL (Uniform Resource Locator) to the item described by the feed. An undecorated URL not be unique if you generated a second RSS item to the same URL when the story changed.

The pubDate uses computer-unfriendly, English-only alphabetic month and day-of-week names of RFC 5322 It won’t accept UTC (Coordinated Universal Time/Temps Universel Coordonné) , only GMT (Greenwich Mean Time) or UT. Java does not support UT. It supports only a subset of the Java TimeZone abbreviations, so it would be dangerous to use Locale default.

Two

To get a browser to notice your feed, you need a special entry in the <head> section

RDF

You can see what a typical RDF feed looks like on this Nature

FeedBurner

You can see what a typical FeedBurner feed looks like on this FeedBurner Blast the Right feed:

Note how it permits you to format the text with HTML tags.

Atom 3

Atom was developed to address some of the problems with the rather Mickey Mouse RSS. The syntax of the feel is called APP (Atom Publishing Protocol). It is defined in RFC 319 and RFC 5023. It is considerably more complicated and includes a server protocol for handling individual items. You can see what a typical Atom feed looks like:

The display is not quite right because the text is being displayed in ISO-8859-1, where the original is in UTF-8. Each item is sandwiched in entry tags. UTF-8 encoding allows special characters without entities. It supports both plain and HTML-formatted text. It allows you to ascribe an author to each entry. The scheme allows you to update entries. There is a mechanism to reply to individual entries, as you would in a blog.

Viewing Feeds

The feed is in XML. Here is how it will render in various browsers:

How Various Browsers Render RSS feeds
How Various Browsers Render RSS Feeds
Browser	How Renders
Opera	Special RSS-feed column format
Firefox	CSS-style sheet HTML. Displays the feed logo.
SeaMonkey	raw HTML tags, colourised
Mozilla	CSS-style sheet HTML
Netscape	CSS-style sheet HTML
IE (Internet Explorer) 7	A blank screen
IE 8	HTML layout

Advantages

A person interested in your website can use a program called rss2email to subscribe to sites of interest. he program polls the feeds every so often and emails anything new. This way, the user does not have to check each site for new stuff; the new stuff is delivered right to the inbox. If the user is interested in a particular item, she can follow the link included in the feed.

Opera browser can manage your RSS feeds. Firefox supports RSS feeds calling them live bookmarks. Some sites refer to them as live feeds.

Because the date of each item is encoded in a standard way, it makes it possible to display just the new unviewed material no matter what the frequency of the automated visiting.

Setting Up a RSS Feed

If you wanted to set up an RSS feed on your website there are several ways to do it:

Use an ordinary text editor to compose an XML file. When the file gets too big, drop the oldest items.
Use any of the tools mentioned below.
You can use Rome to produce RSS feed in various formats. The library handles the differences between supported formats without impacting the developer. Once you have a servlet (or something similar) to produce a feed using Rome, you can hook it up with FeedBurner which will take care of HTML-ing the feed, as well as giving the users options to bookmark it on various social bookmarking sites, add the feed to various readers, provide statistics for the click-thru on the feed items, etc. You can also get a user-friendly URL by doing so. An example of this technique is at Techcrunch.
Roll your own. RSS is not that complicated. In the simplest case, for each item you have a date, a title and a subject wrapped in boilerplate. It is not that difficult to write a program that formats the data is any RSS form and also in HTML ready to include as a side effect. You can hard code the data into a program you compile and run each time you update the feed, or you could put it an CSV (Comma-Separated Value) file or one line per field. Or you might use HTML Static macros to publish the data both in HTML and RSS. You might find that easier than learning a third party package. That is how I do the Java Glossary RSS feed for my own website. I embed magic comments on my webpages that the HTML Static Macro engine finds, sorts, groups and compiles into RSS 2 feeds.

Aggregators

Aggregators are people who will help publicise your feed. They may also proxy it. That means they probe it periodically, then serve it to others. This takes a load off your server. They also convert it to other formats. They may also provide statistics about your feed’s usage. It may also provides tools for syndicating your content (such as embedding headlines into web pages). Aggregators may also convert ordinary blogs into feeds for you too.

Once your feed in operational, you might want to register it with the following aggregators.

RSS feed aggregators
	Technorati
	Google Blog Search	for both blogs and feeds. Google has sunset its Google Reader service.
	Google FeedBurner

Books

recommend book⇒Developing Feeds with RSS and Atom

Ben Hammersley

978-0-596-00881-9

paperback

birth

1976-04-03 age:42

978-1-4493-6598-1

eBook

publisher

O’Reilly

B00BCQ5Q5K

kindle

published

2005-04-13

Covers RSS-2 and Atom to create website update feeds and website update consolidating feeds, especially for news websites.

Online bookstores carrying Developing Feeds with RSS and Atom
	abe books anz	abe books.ca
	abe books.de	amazon.ca
	amazon.de	Chapters Indigo
	amazon.es	Chapters Indigo eBooks
	iberlibro.com	abe books.com
	abe books.fr	amazon.com
	amazon.fr	Barnes & Noble
	abe books.it	Nook at Barnes & Noble
	amazon.it	Kobo
	junglee.com	Google play
	abe books.co.uk	O’Reilly Safari
	amazon.co.uk	Powells
	other stores

Greyed out stores probably do not have the item in stock. Try looking for it with a bookfinder.

Altova XMLSpy: XML editor
CBC.ca RSS2 feed
DMOZ list of RSS newsreaders
FeedBlitz
FeedBurner
firefox add-in RSS editor
Google RSS 2.0 specs: more stringent
MIME
myRSS: gatherer and printer
Opera: browser with RSS feed support
podcast
Real Gagnon on how to to roll your own RSS
Rome: RSS Java classes
RSS 2 DTD
RSS 2.0.10 spec
RSS Feeder .NET: opensource RSS: collect RSS and prepare for blogs
RSS intro
RSS tutorial
RSS workshop: examples
RSSInclude: widgets
rssreader.com: a free RSS reader
rsync
The replicator
Videoblogging
W3C Site Summaries in XHTML uses hints in your HTML to generate a feed

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