RSS feeds with Java

Revision History
Revision 0.1	03.09.2008	Lars Vogel	Created
Revision 0.2 - 2.2	06.03.2013	Lars Vogel	bug fixes and enhancements

1. RSS - Really Simple Syndication

An RSS document is an XML file which can be used to publish blog entries and news. The format of the XML file is specified via the RSS specification.

RSS stands for Really Simple Syndication (in version 2.0 of the RSS specification).

Typically a RSS file is provided by a webserver, which RSS client read. These RSS clients parse the file and display it.

2. Prerequisites

As an RSS feed is a XML file we can use the Java XML parsers to read and create RSS feeds. The following will use the Java Stax XML parser.

For an introduction into XML and its usage with Java see Java XML Tutorial .

3. Project and Domain model

Create the Java project called de.vogella.rss. Create the following Java classes, which is used as domain model.

package de.vogella.rss.model;

/*
 * Represents one RSS message
 */
public class FeedMessage {

  String title;
  String description;
  String link;
  String author;
  String guid;

  public String getTitle() {
    return title;
  }

  public void setTitle(String title) {
    this.title = title;
  }

  public String getDescription() {
    return description;
  }

  public void setDescription(String description) {
    this.description = description;
  }

  public String getLink() {
    return link;
  }

  public void setLink(String link) {
    this.link = link;
  }

  public String getAuthor() {
    return author;
  }

  public void setAuthor(String author) {
    this.author = author;
  }

  public String getGuid() {
    return guid;
  }

  public void setGuid(String guid) {
    this.guid = guid;
  }

  @Override
  public String toString() {
    return "FeedMessage [title=" + title + ", description=" + description
        + ", link=" + link + ", author=" + author + ", guid=" + guid
        + "]";
  }

}

package de.vogella.rss.model;

import java.util.ArrayList;
import java.util.List;

/*
 * Stores an RSS feed
 */
public class Feed {

  final String title;
  final String link;
  final String description;
  final String language;
  final String copyright;
  final String pubDate;

  final List<FeedMessage> entries = new ArrayList<FeedMessage>();

  public Feed(String title, String link, String description, String language,
      String copyright, String pubDate) {
    this.title = title;
    this.link = link;
    this.description = description;
    this.language = language;
    this.copyright = copyright;
    this.pubDate = pubDate;
  }

  public List<FeedMessage> getMessages() {
    return entries;
  }

  public String getTitle() {
    return title;
  }

  public String getLink() {
    return link;
  }

  public String getDescription() {
    return description;
  }

  public String getLanguage() {
    return language;
  }

  public String getCopyright() {
    return copyright;
  }

  public String getPubDate() {
    return pubDate;
  }

  @Override
  public String toString() {
    return "Feed [copyright=" + copyright + ", description=" + description
        + ", language=" + language + ", link=" + link + ", pubDate="
        + pubDate + ", title=" + title + "]";
  }

}

4. Read RSS Feeds with Stax

4.1. Create the XML Reader class

Create the following class to read the XML file.

package de.vogella.rss.read;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Characters;
import javax.xml.stream.events.XMLEvent;

import de.vogella.rss.model.Feed;
import de.vogella.rss.model.FeedMessage;

public class RSSFeedParser {
  static final String TITLE = "title";
  static final String DESCRIPTION = "description";
  static final String CHANNEL = "channel";
  static final String LANGUAGE = "language";
  static final String COPYRIGHT = "copyright";
  static final String LINK = "link";
  static final String AUTHOR = "author";
  static final String ITEM = "item";
  static final String PUB_DATE = "pubDate";
  static final String GUID = "guid";

  final URL url;

  public RSSFeedParser(String feedUrl) {
    try {
      this.url = new URL(feedUrl);
    } catch (MalformedURLException e) {
      throw new RuntimeException(e);
    }
  }

  public Feed readFeed() {
    Feed feed = null;
    try {
      boolean isFeedHeader = true;
      // Set header values intial to the empty string
      String description = "";
      String title = "";
      String link = "";
      String language = "";
      String copyright = "";
      String author = "";
      String pubdate = "";
      String guid = "";

      // First create a new XMLInputFactory
      XMLInputFactory inputFactory = XMLInputFactory.newInstance();
      // Setup a new eventReader
      InputStream in = read();
      XMLEventReader eventReader = inputFactory.createXMLEventReader(in);
      // Read the XML document
      while (eventReader.hasNext()) {
        XMLEvent event = eventReader.nextEvent();
        if (event.isStartElement()) {
          String localPart = event.asStartElement().getName()
              .getLocalPart();
          switch (localPart) {
          case ITEM:
            if (isFeedHeader) {
              isFeedHeader = false;
              feed = new Feed(title, link, description, language,
                  copyright, pubdate);
            }
            event = eventReader.nextEvent();
            break;
          case TITLE:
            title = getCharacterData(event, eventReader);
            break;
          case DESCRIPTION:
            description = getCharacterData(event, eventReader);
            break;
          case LINK:
            link = getCharacterData(event, eventReader);
            break;
          case GUID:
            guid = getCharacterData(event, eventReader);
            break;
          case LANGUAGE:
            language = getCharacterData(event, eventReader);
            break;
          case AUTHOR:
            author = getCharacterData(event, eventReader);
            break;
          case PUB_DATE:
            pubdate = getCharacterData(event, eventReader);
            break;
          case COPYRIGHT:
            copyright = getCharacterData(event, eventReader);
            break;
          }
        } else if (event.isEndElement()) {
          if (event.asEndElement().getName().getLocalPart() == (ITEM)) {
            FeedMessage message = new FeedMessage();
            message.setAuthor(author);
            message.setDescription(description);
            message.setGuid(guid);
            message.setLink(link);
            message.setTitle(title);
            feed.getMessages().add(message);
            event = eventReader.nextEvent();
            continue;
          }
        }
      }
    } catch (XMLStreamException e) {
      throw new RuntimeException(e);
    }
    return feed;
  }

  private String getCharacterData(XMLEvent event, XMLEventReader eventReader)
      throws XMLStreamException {
    String result = "";
    event = eventReader.nextEvent();
    if (event instanceof Characters) {
      result = event.asCharacters().getData();
    }
    return result;
  }

  private InputStream read() {
    try {
      return url.openStream();
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }
}

4.2. Test the code

The following uses a main method to test. You could also use JUnit.

package de.vogella.rss.tests;

import de.vogella.rss.model.Feed;
import de.vogella.rss.model.FeedMessage;
import de.vogella.rss.read.RSSFeedParser;

public class ReadTest {
  public static void main(String[] args) {
    RSSFeedParser parser = new RSSFeedParser("http://www.vogella.de/article.rss");
    Feed feed = parser.readFeed();
    System.out.println(feed);
    for (FeedMessage message : feed.getMessages()) {
      System.out.println(message);

    }

  }
}

5. Write RSS Feeds with Stax

5.1. Create writer

Create the following class to write the XML file.

package de.vogella.rss.write;

import java.io.FileOutputStream;

import javax.xml.stream.XMLEventFactory;
import javax.xml.stream.XMLEventWriter;
import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Characters;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartDocument;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;

import de.vogella.rss.model.Feed;
import de.vogella.rss.model.FeedMessage;

public class RSSFeedWriter {

  private String outputFile;
  private Feed rssfeed;

  public RSSFeedWriter(Feed rssfeed, String outputFile) {
    this.rssfeed = rssfeed;
    this.outputFile = outputFile;
  }

  public void write() throws Exception {

    // Create a XMLOutputFactory
    XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();

    // Create XMLEventWriter
    XMLEventWriter eventWriter = outputFactory
        .createXMLEventWriter(new FileOutputStream(outputFile));

    // Create a EventFactory

    XMLEventFactory eventFactory = XMLEventFactory.newInstance();
    XMLEvent end = eventFactory.createDTD("\n");

    // Create and write Start Tag

    StartDocument startDocument = eventFactory.createStartDocument();

    eventWriter.add(startDocument);

    // Create open tag
    eventWriter.add(end);

    StartElement rssStart = eventFactory.createStartElement("", "", "rss");
    eventWriter.add(rssStart);
    eventWriter.add(eventFactory.createAttribute("version", "2.0"));
    eventWriter.add(end);

    eventWriter.add(eventFactory.createStartElement("", "", "channel"));
    eventWriter.add(end);

    // Write the different nodes

    createNode(eventWriter, "title", rssfeed.getTitle());

    createNode(eventWriter, "link", rssfeed.getLink());

    createNode(eventWriter, "description", rssfeed.getDescription());

    createNode(eventWriter, "language", rssfeed.getLanguage());

    createNode(eventWriter, "copyright", rssfeed.getCopyright());

    createNode(eventWriter, "pubdate", rssfeed.getPubDate());

    for (FeedMessage entry : rssfeed.getMessages()) {
      eventWriter.add(eventFactory.createStartElement("", "", "item"));
      eventWriter.add(end);
      createNode(eventWriter, "title", entry.getTitle());
      createNode(eventWriter, "description", entry.getDescription());
      createNode(eventWriter, "link", entry.getLink());
      createNode(eventWriter, "author", entry.getAuthor());
      createNode(eventWriter, "guid", entry.getGuid());
      eventWriter.add(end);
      eventWriter.add(eventFactory.createEndElement("", "", "item"));
      eventWriter.add(end);

    }

    eventWriter.add(end);
    eventWriter.add(eventFactory.createEndElement("", "", "channel"));
    eventWriter.add(end);
    eventWriter.add(eventFactory.createEndElement("", "", "rss"));

    eventWriter.add(end);

    eventWriter.add(eventFactory.createEndDocument());

    eventWriter.close();
  }

  private void createNode(XMLEventWriter eventWriter, String name,

  String value) throws XMLStreamException {
    XMLEventFactory eventFactory = XMLEventFactory.newInstance();
    XMLEvent end = eventFactory.createDTD("\n");
    XMLEvent tab = eventFactory.createDTD("\t");
    // Create Start node
    StartElement sElement = eventFactory.createStartElement("", "", name);
    eventWriter.add(tab);
    eventWriter.add(sElement);
    // Create Content
    Characters characters = eventFactory.createCharacters(value);
    eventWriter.add(characters);
    // Create End node
    EndElement eElement = eventFactory.createEndElement("", "", name);
    eventWriter.add(eElement);
    eventWriter.add(end);
  }
}

5.2. Test the code

The following uses a main method to test.

Run the program to write the articles.rss file.

package de.vogella.rss.tests;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Locale;

import de.vogella.rss.model.Feed;
import de.vogella.rss.model.FeedMessage;
import de.vogella.rss.write.RSSFeedWriter;

public class WriteTest {

  public static void main(String[] args) {
    // Create the rss feed
    String copyright = "Copyright hold by Lars Vogel";
    String title = "Eclipse and Java Information";
    String description = "Eclipse and Java Information";
    String language = "en";
    String link = "http://www.vogella.de";
    Calendar cal = new GregorianCalendar();
    Date creationDate = cal.getTime();
    SimpleDateFormat date_format = new SimpleDateFormat("EEE', 'dd' 'MMM' 'yyyy' 'HH:mm:ss' 'Z", Locale.US);
    String pubdate = date_format.format(creationDate);
    Feed rssFeeder = new Feed(title, link, description, language,
        copyright, pubdate);

    // Now add one example entry
    FeedMessage feed = new FeedMessage();
    feed.setTitle("RSSFeed");
    feed.setDescription("This is a description");
    feed.setAuthor("nonsense@somewhere.de (Lars Vogel)");
    feed.setGuid("http://www.vogella.de/articles/RSSFeed/article.html");
    feed.setLink("http://www.vogella.de/articles/RSSFeed/article.html");
    rssFeeder.getMessages().add(feed);

    // Now write the file
    RSSFeedWriter writer = new RSSFeedWriter(rssFeeder, "articles.rss");
    try {
      writer.write();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

}

6. Thank you

Please help me to support this article:

7. Questions and Discussion

Before posting questions, please see the vogella FAQ. If you have questions or find an error in this article please use the www.vogella.com Google Group. I have created a short list how to create good questions which might also help you.

8. Links and Literature

http://feedvalidator.org/ Webpage which validates feeds