Crawling the Semantic Web, concluded

In the previous section, we used the Informa library to create RSS content, so that visitors with content aggregators can be automatically informed about updates to your site. Another great use of RSS within your site is displaying recent news related to your industry. You can get these newsfeeds from many sources, such as news sites, websites in your industry, and aggregator sites like Syndic8. Make sure to check whether the sites you are syndicating will allow you to incorporate items from their feeds into your site. Usually this is the case, but not always.

Let’s start by reading items from a newsfeed and displaying them as text. Using Informa, reading an RSS feed is easy. You can populate the same ChannelBuilder object that we used in the previous section with data from an existing RSS feed. The FeedParser class has a parse method that returns a ChannelIF instance containing the channel data from the RSS feed. The RSS standards may be in a state of confusion, but the Informa API reads all of them and gives us a common object model for working with them.

import de.nava.informa.impl.basic.Channel;
import de.nava.informa.impl.basic.ChannelBuilder;
import de.nava.informa.impl.basic.Item;
import de.nava.informa.parsers.FeedParser;

ChannelBuilder builder = new ChannelBuilder();
String url = "http://wickedcooljava.com/updates.rss";
Channel channel = (Channel) FeedParser.parse(builder, url);
System.out.println("Description: " + channel.getDescription());
System.out.println("Title: " + channel.getTitle());
System.out.println("====================================");
// using Java 5 syntax in this for loop
for (Object x : channel.getItems())
{
  Item anItem = (Item) x;
  System.out.print(anItem.getTitle() + " - ");
  System.out.println(anItem.getDescription());
}

This will print some basic information about the channel and its items. If you want to include these in a web page, it’s now just a matter of wrapping HTML tags around the text. If you are including RSS files that are outside your control, you may want to filter data from the channels before displaying them. We’ll discuss this in a later section.