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Parsing RSS Feeds Using ColdFusion

Parsing RSS Feeds Using ColdFusion

XML is popping up all over the Internet and the need to transfer information from system to system, independent of the platform, is greater then ever. XML (eXtensible Markup Language) allows you to define your own human readable markup language (similar to HTML).

Many vendors are now operating with XML, due to the fact that it is text based and platform independent. A number of XML-based standards have already been created to facilitate data exchange. This article will focus on one of these standards, and probably the most popular, RSS. In this article you'll learn how to read and parse an RSS document using the ColdFusion MX XML tags and functions, and some tips will be offered on how you can aggregate the data for later use.

What Is RSS?
RSS is an XML 1.0-based standard that was developed by Netscape to transfer data between Web sites from their portal environment. It is not any different than any other standard and has an umbrella of different versions that have been developed by different organizations. The original specification was developed by Netscape as a format to supply news items from their portal environment to other news Web sites. When Netscape withdrew from the portal business, RSS was also subsequently dropped from development. Other software vendors (most notably Userland Software) picked up the idea and continued to develop it.

Today, there are many different versions of RSS in use: version 0.91, which was standardized by Netscape; versions 0.92, 0.93, 0.94, and 2.0, which were developed by Userland; and version 1.0 (also called RDF), which was developed by independent organizations.

As with most XML documents, the meaning and content can be fairly easily gleaned by simply looking at it. Many Web sites now provide a summary of their content through RSS documents, such as Macromedia (www.markme.com/mxna/blogview.cfm?blogid=8). Also, more and more industry leaders such as Jeremy Allaire (http://radio.weblogs.com/0113297) and Kevin Lynch (www.klynch.com) are now sharing their thoughts through weblogs that are also publishing their content using the RSS standard.

This article will concentrate mainly on version 0.91 (RSS 0.91) since it is the simplest form of RSS, but the techniques represented in this article will apply for most versions of RSS and other XML documents. Listing 1 shows a sample of a basic RSS version 0.91 document.

The XML document starts with the <channel> tags which include the title, description, and URL of the site the document is describing along with items that the channel currently contains. For each <item> tag, there is a title of the article, the description, and a URL that points back to the original Web site. Take note that this is a bare bones RSS document and that most documents that are in use have more metadata such as author, publish date, and images.

ColdFusion and XML - Parsing
Because RSS provides an easy way for Web sites and weblogs to share data, we now have a wealth of information at our fingertips. This overload of information also means that we need some way to compile it all, in order to make it easier and faster to read. The following section will describe the methods you can use to read an XML document.

There are two methods widely used to parse XML. The first is API-based functions; the second is a Document Object Model (DOM). When using a DOM, the XML document is read into memory and manipulated through functions that are provided. The DOM approach is generally considered much more powerful. However, it suffers from serious drawbacks that include the inability to process large documents (mainly due to memory constraints).

ColdFusion MX offers you a set of functions to process XML. It is these functions that we will use to parse our RSS document and create the aggregator.

The first step of the aggregator is to retrieve the RSS document. We accomplish this by using the <CFHTTP> tag and pointing it to the URL of the RSS document.

<cfhttp url="http://www.mywebsite.com/rss091.xml" method="get">

The next step is to use the XMLParse() ColdFusion function and create an XML document using the text that we have already retrieved with the <CFHTTP>:

<cfset objRSS = xmlParse(cfhttp.filecontent)>

Creating an XML object will parse the XML document into a series of XML elements and structures that will enable us to use the predefined ColdFusion variables to manipulate the RSS document. If you wish to view the structure of the XML document you can perform this command after you have done the XMLParse():

<CFDUMP var="#objRSS#">

Once the object has been parsed by ColdFusion, you are now ready to retrieve the document meta data and the items. The data within the object can be retrieved by referencing each XML node using the hierarchy of the document beginning by the root node. For example, if we would like to retrieve the text within the <title> tag of the channel we do the following:

<cfoutput> #objRSS.channel.title.xmltext# </cfoutput>

Xmltext is a special reserved variable created when ColdFusion parses an XML object, which is used to refer to the data appearing between a given XML element's open and closing tags. We can easily reference the <title>, <link>, and <description> tags under the channel, but we still need to retrieve the data from the <item>s. Since there is more than one <item> element in the document, we cannot reference them by doing the following because ColdFusion will not know which item to retrieve:

<cfoutput> #objRSS.channel.item.title.xmltext# </cfoutput>

The ColdFusion MX XMLParse() function gets around this issue by creating an Array with the elements when it encounters more than one of the same name within a given parent. The array permits us to reference each item like this:

<cfoutput> #objRSS.channel.item[1].title.xml text# </cfoutput>

In our example we use a <CFLOOP> to loop through all the <item> tags. We use the following ArrayLen() function to identify the number of <item> tags:

<cfset Item_Length = arraylen(objRSS.channel.item)>

Listing 2 has the complete listing of the XML parser with all the tags and functions described in this section. Notice that the XmlParse function is wrapped in a CFTRY statement. Since the file being retrieved may or may not be a properly formatted XML document and could throw an error, it would be wise to handle any such error this way.

The Next Step
Now that you have retrieved all the data from the RSS document, you'll probably want to do something useful with it. The next step would most likely be to take the data that you have retrieved and insert it into a database, and then create a front end interface to view the data. Also, since most RSS documents are created dynamically and change on a regular basis, it's a good idea to create a scheduled task in the ColdFusion administrator to run your RSS parser/database update on a regular basis.

Conclusion
Hopefully this article has shown you how to properly parse and display an RSS document using the ColdFusion functions and will get the ideas flowing in your mind. More thought would be required to create an RSS aggregator that can be used on your Web site or intranet. Although we used the RSS standards as an example, you can use the same function and ideas to create a parser and aggregators for any XML document.

Resources
If you would like to purchase an RSS aggregator for your Web site as opposed to creating your own, you can have a look at the Macromedia DevNet Resource Kit Volume 3 (www.macromedia.com/software/drk/ productinfo/product_overview/volume3). Not only does the DRK3 come with its own aggregator, it also allows you to create and manage your own RSS feeds.

More information on the RSS standards is available at: http://backend.userland.com/rss, http://backend.userland.com/rss091, http://web.resource.org/rss/1.0/spec.

More information on the ColdFusion XML Functions is available at: http://livedocs.macromedia.com/cfmxdocs/ CFML_Reference/functions-pt022.jsp#3468770

More Stories By Domenic Plouffe

Dominic Plouffe, cofounder and VP R&D of FuseTalk, Inc., has been designing Web applications since 1997.

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