a cup of java

Almost two years back I posted a SAX based RSS parser (find it here) which was intented for J2ME. But we have JDOM parser which I think is a lot easier than SAX. In this post you can find a very simple JDOM based RSS parser.

Know more about RSS here: http://en.wikipedia.org/wiki/RSS_(file_format)

Step1: Import the JDOM libraries

import org.jdom.Document;
import org.jdom.Element;
import org.jdom.input.SAXBuilder;

Step 2: Initialize

// I have not given the implementation of
// getUrlConnectionInputStream(url)
inputStream = getUrlConnectionInputStream(url);
if(null == inputStream)
   throw new Exception("No input stream for " + url);

saxBuilder = new SAXBuilder();
document = saxBuilder.build(inputStream);
rssFeed = _build(document);

Step 3: Implementation of _build(org.jdom.Document)

// Entry point. Returns a RssFeed object corresponding
// to the given RSS feed URL
private RssFeed _build(Document document)
throws Exception
{
  RssFeed rssFeed = null;
  Element rootElement = null;
  Element channelElement = null;
  String  rssFeedVersion = null;

  if (null == document)
    throw new Exception("Empty document");

  rootElement = document.getRootElement();
  if (!"rss".equalsIgnoreCase(rootElement.getName()))
    throw new Exception("Invalid XML");

  rssFeedVersion = rootElement.getAttributeValue("version");
  channelElement = rootElement.getChild("channel");
  if (null == channelElement)
    throw new Exception("Empty feed");

  // Getting the feed contents
  rssFeed = _getHeader(channelElement);
  rssFeed.version = rssFeedVersion;
  _addFeedItems(channelElement, rssFeed);

  return (rssFeed);
}

Step 4: _getHeader(org.jdom.Element)

This method reads the feed header and sets the values to the RssFeed object.

// Sets the RSS feed heder information to the
// RssFeed object
rssFeed = new RssFeed();
rssFeed.title = getValueOfChildElement(channelElement, "title");
rssFeed.link = getValueOfChildElement(channelElement, "link");
rssFeed.description = getValueOfChildElement(channelElement, "description");

Step 5: _addFeedItems(org.jdom.Elements,  subin.xml.RssFeed)

This method extracts each feed item from the XML and adds it to the given RssFeed object.

// Iterates through the feed item list, extracts the
// feed item details, creates corresponding RssItem object
// and adds it to the RssFeed item list
java.util.List<element> itemElements = null;
RssItem anRssItem = null;

itemElements = channelElement.getChildren("item");
if (null != itemElements)
{
  for (Element anItemElement : itemElements)
  {
    anRssItem = new RssItem();
    anRssItem.title = getValueOfChildElement(anItemElement, "title");
    anRssItem.link = getValueOfChildElement(anItemElement, "link");
    anRssItem.description = getValueOfChildElement(anItemElement, "description");
    anRssItem.pubDate = getValueOfChildElement(anItemElement, "pubDate");
    rssFeed.addItem(anRssItem);
  }
}

Step 6: getValueOfChildElement(org.jdom.Element, String)

This method extract the value of the child node (specified by the name) from the given JDOM Element.

// Get the child node value
private String getValueOfChildElement(Element parentElement,
  String tagName)
{
  Element childElement = null;
  String  tagValue     = null;
  childElement = parentElement.getChild(tagName);
  tagValue = (null != childElement)
    ? childElement.getValue().trim() : null;
  return (tagValue);
}

Step 7: RssFeed & RssItem

Two classes to hold the feed information.

class RssFeed
{
  public  String version;
  public  String title;
  public  String description;
  public  String link;

  public List <rssitem> items;
}

class RssItem
{
  public  String title;
  public  String description;
  public  String link;
  public  String pubDate;
}

If you find it difficult to follow as it is not a single file, I’m very sorry. But I hope this will be useful.

RSS (Really Simple Syndication)
RSS is way to publish frequently changing contents like blog posts, news updates, stock quotes & things like that. An RSS document, which is called a “feed,” “web feed,” or “channel,” contains either a summary of content from an associated web site or the full text. RSS formats are specified using XML, a generic specification for the creation of data formats.

I have attached a simple SAX parser for RSS. Please let me know if there is any flaw in the attached code. This code is provided for learning purpose with less focus on coding standards & it’s efficiency. You are free to use & modify it.

package subin.rnd.xml;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Properties;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;

public class RssParser extends DefaultHandler
{  
    private String        urlString;
    private RssFeed       rssFeed;
    private StringBuilder text;
    private Item          item;
    private boolean       imgStatus;
   
    public RssParser(String url)
    {
        this.urlString = url;
        this.text = new StringBuilder();
    }
   
    public void parse()
    {
        InputStream urlInputStream = null;
        SAXParserFactory spf = null;
        SAXParser sp = null;
       
        try
        {
            URL url = new URL(this.urlString);
            _setProxy(); // Set the proxy if needed
            urlInputStream = url.openConnection().getInputStream();           
            spf = SAXParserFactory.newInstance();
            if (spf != null)
            {
                sp = spf.newSAXParser();
                sp.parse(urlInputStream, this);
            }
        }

        /*
         * Exceptions need to be handled
         * MalformedURLException
         * ParserConfigurationException
         * IOException
         * SAXException
         */
       
        catch (Exception e)
        {
            System.out.println("Exception: " + e);
            e.printStackTrace();
        }
        finally
        {
            try
            {
                if (urlInputStream != null) urlInputStream.close();
            }
            catch (Exception e) {}
        }
    }

    public RssFeed getFeed()
    {
        return (this.rssFeed);
    }
   
    public void startElement(String uri, String localName, String qName,
            Attributes attributes)
    {
        if (qName.equalsIgnoreCase("channel"))
            this.rssFeed = new RssFeed();
        else if (qName.equalsIgnoreCase("item") && (this.rssFeed != null))
        {
            this.item = new Item();
            this.rssFeed.addItem(this.item);
        }
        else if (qName.equalsIgnoreCase("image") && (this.rssFeed != null))
            this.imgStatus = true;
    }
   
    public void endElement(String uri, String localName, String qName)
    {
        if (this.rssFeed == null)
            return;
       
        if (qName.equalsIgnoreCase("item"))
            this.item = null;
       
        else if (qName.equalsIgnoreCase("image"))
            this.imgStatus = false;
       
        else if (qName.equalsIgnoreCase("title"))
        {
            if (this.item != null) this.item.title = this.text.toString().trim();
            else if (this.imgStatus) this.rssFeed.imageTitle = this.text.toString().trim();
            else this.rssFeed.title = this.text.toString().trim();
        }       
       
        else if (qName.equalsIgnoreCase("link"))
        {
            if (this.item != null) this.item.link = this.text.toString().trim();
            else if (this.imgStatus) this.rssFeed.imageLink = this.text.toString().trim();
            else this.rssFeed.link = this.text.toString().trim();
        }       
       
        else if (qName.equalsIgnoreCase("description"))
        {
            if (this.item != null) this.item.description = this.text.toString().trim();
            else this.rssFeed.description = this.text.toString().trim();
        }
       
        else if (qName.equalsIgnoreCase("url") && this.imgStatus)
            this.rssFeed.imageUrl = this.text.toString().trim();
       
        else if (qName.equalsIgnoreCase("language"))
            this.rssFeed.language = this.text.toString().trim();
       
        else if (qName.equalsIgnoreCase("generator"))
            this.rssFeed.generator = this.text.toString().trim();
       
        else if (qName.equalsIgnoreCase("copyright"))
            this.rssFeed.copyright = this.text.toString().trim();
       
        else if (qName.equalsIgnoreCase("pubDate") && (this.item != null))
            this.item.pubDate = this.text.toString().trim();
       
        else if (qName.equalsIgnoreCase("category") && (this.item != null))
            this.rssFeed.addItem(this.text.toString().trim(), this.item);
       
        this.text.setLength(0);
    }
   
    public void characters(char[] ch, int start, int length)
    {
        this.text.append(ch, start, length);
    }
   
    public static void _setProxy()
    throws IOException
    {
        Properties sysProperties = System.getProperties();
        sysProperties.put("proxyHost", "<Proxy IP Address>");
        sysProperties.put("proxyPort", "<Proxy Port Number>");
        System.setProperties(sysProperties);
    }
  
    public static class RssFeed
    {
        public  String title;
        public  String description;
        public  String link;
        public  String language;
        public  String generator;
        public  String copyright;
        public  String imageUrl;
        public  String imageTitle;
        public  String imageLink;
       
        private ArrayList <Item> items;
        private HashMap <String, ArrayList <Item>> category;
       
        public void addItem(Item item)
        {
            if (this.items == null)
                this.items = new ArrayList<Item>();
            this.items.add(item);
        }
       
        public void addItem(String category, Item item)
        {
            if (this.category == null)
                this.category = new HashMap<String, ArrayList<Item>>();
            if (!this.category.containsKey(category))
                this.category.put(category, new ArrayList<Item>());
            this.category.get(category).add(item);
        }
    }
   
   
    public static class Item
    {
        public  String title;
        public  String description;
        public  String link;
        public  String pubDate;
       
        public String toString()
        {
            return (this.title + ": " + this.pubDate + "n" + this.description);
        }
    }
   
}

Using RssParser.java :

RssParser rp = new RssParser("<RSS Feed URL>");
rp.parse();
RssFeed feed = rp.getFeed();

// Listing all categories & the no. of elements in each category
if (feed.category != null)
{
 System.out.println("Category List: ");
 for (String category : feed.category.keySet())
 {
  System.out.println(category
    + ": "
    + ((ArrayList<Item>)feed.category.get(category)).size());
 }
}

// Listing all items in the feed
for (int i = 0; i < feed.items.size(); i++)
 System.out.println(feed.items.get(i).title);