Parsing RSS-XML using JSTL tag library

RSS, or Really Simple Syndication, is a method of sharing and broadcasting content such as news from a website. Using XML, items such as news articles can be automatically downloaded into a News Reader or published onto another website. There are two ways of using RSS; to share your data with others or to harvest others’ data for your site. First version of RSS called RDF Site Summary was created by Ramanathan V. Guha at Netscape in March 1999. This version became known as RSS 0.9. Version 0.91 was launched by Dan Libby of Netscape in July 1999. He also renamed RSS “Rich Site Summary”.

Introduction to JSTL

Java Server Pages Standard Tag Library is a component of Java Enterprise Edition Web application development platform (J2EE 1.4 SDK) released by Sun Microsystems. JSTL provides an effective way to embed logic within a JSP page without using embedded Java code directly. The use of a standardized tag set, rather than breaking in and out of Java code leads to more maintainable code and enables separation of concerns between the development of the application code and user interface.

Commonly used JAR files

Parsing XML using JSTL

The x prefix type of tag of JSTL can be used for parsing xml documents. Let us keep the XML content in a file called data.xml. Following is the content of data.xml

<!-- Filename: data.xml -->
<persons>
 <student>
  <name>Mary</name>
  <age>12</age>
  <class>5</class>
 </student>
 <student>
  <name>John</name>
  <age>13</age>
  <class>6</class>
 </student>
</persons>
Code language: HTML, XML (xml)

Assume that this file is placed next to JSP file where we need to parse this xml document. Following will be the JSP file which will parse data.xml file and display information of each student as a row in table. Content of ShowStudents.jsp

<!-- Filename: ShowStudents.jsp -->
<%@taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="x"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<HTML>
<HEAD>
 <TITLE>Display Student Information</TITLE>
 <STYLE>
  table {border: 1px solid blue; width: 300px;}
 </style>
</HEAD>
<BODY>
 
 <c:import var="xmlDoc" url="data.xml"/>
 
 <x:parse var="parsedDocument" xml="${xmlDoc}"/>
 <table>
  <tr>
   <th>Name</th>
   <th>Age</th>
   <th>Class</th>
  </tr>
  <x:forEach select="$parsedDocument/persons/student">
  <tr>
   <td> <x:out select="name" /> </td>
   <td> <x:out select="age" /> </td>
   <td> <x:out select="class" /> </td>
  </tr>
  </x:forEach>
 </table>
</BODY>
</HTML>
Code language: HTML, XML (xml)

Understanding the code To parse a given XML document, first we need to import it using <c:import> tag. This tag will import the content of the url into a variable. In previous example, content of the data.xml will be copied into variable xmlDoc. For parsing the imported XML content, <x:parse> tag is used. Hence the parsedDocument variable will contain parsed XML document. This variable can be used then to access other child tags as well as properties. <x:forEach> tag can be used to iterate across a given tag. Here in above example we have iterated through <student> tag by using <x:forEach select=”$parsedDocument/persons/student”>. Child elements of <student> tag can be accessed by <x:out select=”name” />. Hence this tag will print the value of the <name> tag.

Understanding structure of RSS 2.0

Since RSS 2.0 must be a valid XML, the first line of the feed must be the XML declaration.

<?xml version="1.0"?>
Code language: HTML, XML (xml)

The root of the RSS 2.0 format is <rss> and <channel> tag. All of the feed content goes inside these tags.

<rss version="2.0">
  <channel>
Code language: HTML, XML (xml)

Next comes the information about the feed such as title of feed, the description, like of the site etc.

<title>Google News Feed</title>
<link>http://news.google.com</link>
<description>Google News Feed</description>
<language>en-us</language>
<pubDate>Tue, 10 Jun 2008 04:00:00 GMT</pubDate>
<lastBuildDate>Tue, 10 Jun 2008 09:41:01 GMT</lastBuildDate>
Code language: HTML, XML (xml)

A channel may contain any number of <item>s. An item may represent a “story” — much like a story in a newspaper or magazine; if so its description is a synopsis of the story, and the link points to the full story. An item may also be complete in itself, if so, the description contains the text (entity-encoded HTML is allowed), and the link and title may be omitted. All elements of an item are optional, however at least one of title or description must be present. Each item has a title, link, description, publication date and guid.

<item>
  <title>Star City</title>
  <link>http://liftoff.msfc.nasa.gov/news/2003/news-starcity.asp</link>
  <description>
     How do Americans get ready to work with Russians aboard the International Space Station? 
</description>
  <pubDate>Tue, 03 Jun 2008 09:39:21 GMT</pubDate>
  <guid>http://liftoff.msfc.nasa.gov/2008/06/03.html </guid>
</item>
Code language: HTML, XML (xml)

title: The name of the channel.
link: The URL to the HTML website corresponding to the channel
language: The language the channel is written in
copyright: Copyright notice for content in the channel.
managingEditor: Email address for person responsible for editorial content.
webMaster: Email address for person responsible for technical issues relating to channel.
pubDate: The publication date for the content in the channel.
category: Specify one or more categories that the channel belongs to.
generator: A string indicating the program used to generate the channel.
image Specifies: a GIF, JPEG or PNG image that can be displayed with the channel.

Elements of <item>

title: The title of the item.
link: The URL of the item.
description: The item synopsis.
author: Email address of the author of the item.
category: Includes the item in one or more categories.
comments: URL of a page for comments relating to the item.
enclosure: Describes a media object that is attached to the item
guid: A string that uniquely identifies the item.
pubDate: Indicates when the item was published.
source: The RSS channel that the item came from.

Parsing RSS using JSTL

We will create a parser which parse the given RSS feed and will display it in a JSP using JSTL. For this we will have a textbox where in user can specify the Feed URL. This URL will be submitted to same JSP page and then will be parsed using tag of JSTL.

<!-- Filename: FeerReader.jsp -->
<%@taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="x"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<HTML>
<HEAD>
 <TITLE>Feed Reader in JSTL</TITLE>
 <STYLE>
  table 
             {border: 2px ridge ; width: 500px}
  #feed .title
             {font-family: Arial; font-weight: bold; font-size: 18px}
  #feed .label
             {font-family: Tahoma; font-weight: bold; font-size: 11px}
  #feed td 
             {font-family: Tahoma; font-size: 11px}
 </style>
</HEAD>
<BODY>
 <form>
  <input type="text" name="feedURL" 
   value="http://news.google.com/?output=rss" /> 
  <input type="submit" value="Display"/>
 </form>

 <c:if test="${param.feedURL != null}">
  
 Feed URL: ${param.feedURL}

   <c:import var="xmlContent" url="${param.feedURL}"/>
 
 <x:parse var="doc" xml="${xmlContent}"/>
     
     
    <table class="content-table"" id="feed">
    <tr class="profile_odd">
     <td align="center" colspan="2">  
      <span class="title">
               <x:out select="$doc/rss/channel/title" />
      </span> 
     </td>
    </tr>
     <x:forEach var="story" 
                select="$doc/rss/channel/item" varStatus="status">
      <tr>
       <td colspan="2"> <hr/> </td>
      </tr>
        <tr class="profile_even">
          <td class="label">Topic</td>
          <td> <x:out select="title" /> </td> 
        </tr>
        <tr class="profile_even">
          <td class="label">Published Date</td>
          <td> <x:out select="pubDate" /> </td> 
        </tr>
        <tr class="profile_even">
          <td class="label">Category</td>
          <td> <x:out select="category" /> </td> 
        </tr>
        <tr class="" valign="top">
         <td class="label">Description</td>
         <td><x:out select="description" escapeXml="false"/></td>
        </tr>
      </x:forEach>
    </table>
 </c:if>
</BODY>
</HTML>
Code language: HTML, XML (xml)

References

JSTL Home Page (https://java.sun.com/products/jsp/jstl/)
Documentation on XML tag library (http://java.sun.com/j2ee/1.4/docs/tutorial/doc/JSTL5.html)
Information about RSS (http://en.wikipedia.org/wiki/RSS_(file_format))

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