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syndication feeds on our computers.
In this chapter, we develop our own client application, an XML reader that obtains feeds from various websites. It can be run in the browser on any computer that has an active Internet connection.
13.1 Reading information from the outside world
An XML syndication feed consists of articles that are freely available for the public to read and display on other websites. A blog is good example of a syndicated XML feed for our purposes because it is so widely available. These XML feeds are different from plain old articles on a website since they can be shared and displayed in multiple formats. It is like finding a newspaper or magazine that fits perfectly on your table as you eat your morning breakfast. You can eat and read at the same time without having to shift everything around and spilling your coffee. The syndicated feeds can be formatted in any style that fits your needs, allowing you to obtain just the information you want.
We can view the contents of an XML syndication feed in several ways. For instance, for a single blog, we could go to the website where the XML feed is located. To view several feeds at once, we could go to sites such as JavaCrawl.com, which allow us to view multiple XML feeds without going to multiple sites. We can also view the RSS feed in its raw unedited form by directly opening up the path of the XML file directly in our web browser, or we can use downloadable software to organize and format the feeds we want to see.
A new option is to use Ajax to view the syndication feeds. Without Ajax, we were stuck with downloading a client application or having to visit a website to Licensed to jonathan zheng Reading information from the outside world 505 grab this information, but with Ajax we do not have to download anything or visit a website. Instead we are able to develop a JavaScript-based RSS reader that can be run directly on our desktop with just a browser. In this chapter, we build an application that obtains multiple RSS feeds from multiple sources and allows us to view them in an orderly fashion. We also integrate transition effects to add to the flashiness of the user interface. But before we develop this application with Ajax, we need to understand the format of an XML feed and where we can find XML feeds. 13.1.1 Discovering XML feeds One of the most popular places to find an XML feed is on a blog. Many people today publish blogs, for all kinds of reasons. They can contain information such as a personal diary, personal musings, news articles, jokes, or technology discussions. Let’s look at one example of a blog by Eric Pascerello, in figure 13.1. Eric’s blog is accessible, which means that it can be linked to by anyone. While many people simply read it on the JavaRanch site, it can also be accessed as a syndication feed. We can read this feed by accessing it directly in its native XML form, or we can go to other websites (such as JavaLobby) that obtain the syndication feed and display it in their format. Figure 13.1 Eric Pascarello’s blog, which has an accessible RSS feed Licensed to jonathan zheng 506 CHAPTER 13 Building stand-alone applications with Ajax In figure 13.1, we see in the upper-right corner of the screen that there are links to RSS, RDF, and Atom. As we mentioned earlier, these are the most common XML syndication feeds that we can find. Each of the syndication feeds has a different XML specification. That means if we were to look at the different XML files, we would see different naming schemes for the elements. Each feed has a specification clarifying what information must be defined in the feed. Since we are dealing with different formats, the easiest way to address it is to pick a single format and design the reader around it. One of the most popular syndication feeds is Really Simple Syndication, better known as the RSS feed. 13.1.2 Examining the RSS structure Before we create our Ajax XML reader,