Rome v0.3 Tutorial, Using Rome to convert a syndication feed from one type to another

Software requirements: Synd J2SE 1.4+, JDOM B10 and Rome 0.3.

Rome represents syndication feeds (RSS and Atom) as instances of the com.rometools.rome.synd.SyndFeedI interface. The SyndFeedI interfaces and its properties follow the Java Bean patterns. The default implementations provided with Rome are all lightweight classes.

Rome includes parsers to process syndication feeds into SyndFeedI instances. The SyndFeedInput class handles the parsers using the correct one based on the syndication feed being processed. The developer does not need to worry about selecting the right parser for a syndication feed, the SyndFeedInput will take care of it by peeking at the syndication feed structure. All it takes to read a syndication feed using Rome are the following 2 lines of code:

SyndFeedInput input = new SyndFeedInput();
SyndFeedI feed = input.build(new InputStreamReader(feedUrl.openStream()));

Obtaining the char based input stream has been simplified in this tutorial, the sample code in the distribution is a little more complex to handle charset encodings properly.

The first line creates a SyndFeedInput instance that will work with any syndication feed type (RSS and Atom versions). The second line instructs the SyndFeedInput to read the syndication feed from the InputStream of a URL pointing to the feed. The SyndFeedInput.build() method returns a SyndFeedI instance that can be easily processed.

Rome also includes generators to create syndication feeds out of SyndFeedI instances. The SyndFeedOutput class does this generation. The SyndFeedOutput will generate a syndication feed of the feed type indicated by the SyndFeedI object being output. The following two lines of code show how to create a syndication feed output from a SyndFeedI instance:

SyndFeedOutput output = new SyndFeedOutput();
output.output(feed,new PrintWriter(System.out));

The first line creates a SyndFeedOutput instance that will produce syndication feeds. It can output feeds of any type (rss_0.9, rss_0.91, rss_0.92, rss_0.93, rss_0.94, rss_1.0, rss_2.0 & atom_0.3), the SyndFeedI feedType property indicates the type. The second line writes the SyndFeedI as a syndication feed into the application's output.

Following is the full code for a Java application that reads a syndication feed and converts it to other syndication feed type, writing the converted feed to the application's output.

package com.rometools.rome.samples;

import java.net.URL;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import com.rometools.rome.feed.synd.SyndFeedI;
import com.rometools.rome.io.SyndFeedInput;
import com.rometools.rome.io.SyndFeedOutput;

/**
 * It Converts any RSS/Atom feed type to a an RSS/Atom feed of the
 * specified type.
 * <p>
 * @author Alejandro Abdelnur
 *
 */
public class FeedConverter {

    public static void main(String[] args) {
        boolean ok = false;
        if (args.length==2) {
            try {
                String outputType = args[0];

                URL feedUrl = new URL(args[1]);

                SyndFeedInput input = new SyndFeedInput();
                SyndFeedI feed = input.build(new InputStreamReader(feedUrl.openStream()));
                feed.setFeedType(outputType);
                SyndFeedOutput output = new SyndFeedOutput();
                output.output(feed,new PrintWriter(System.out));

                ok = true;
            }
            catch (Exception ex) {
                System.out.println("ERROR: "+ex.getMessage());
            }
        }

        if (!ok) {
            System.out.println();
            System.out.println("FeedConverter converts between syndication feeds types.");
            System.out.println("The first parameter must be the feed type to convert to.");
            System.out.println(" [valid values are: rss_0.9, rss_0.91, rss_0.92, rss_0.93, ]");
            System.out.println(" [                  rss_0.94, rss_1.0, rss_2.0 & atom_0.3  ]");
            System.out.println("The second parameter must be the URL of the feed to convert.");
            System.out.println();
        }
    }

}