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Publishing And Reading RSS Feeds In ASP.NET

What Is RSS?

RSS or Really Simple Syndication (version 2.0) is a method of publishing and displaying almost any type of data over the internet. The most well-known RSS feeds are news and weather related ones provided by publishers like BBC, Yahoo News, Telegraph India, etc. RSS publishing is not only related to news, anyone can publish data from a persistent database as he or she generates the output in the XML format supported and understood by RSS protocol.

 

These feeds are specially useful when people want to display information on their websites which are maintained and updated regularly by a third party agency. This saves time and effort in collecting and maintaining the same data all over again.

RSS feeds have their outputs as XML formats with specific tags like <channel/>, <title/>, <link/>, <description/>, etc. While reading the RSS feeds, the subscriber must be aware of the structure of the feed. A sample RSS feed is as follows which may be published over the internet for some subscriber to access.

<rss version="2.0">
     <channel>
         <title>Employee Details</title>
         <link>http://localhost/RSSFeeds</link>
         <description>Details of all Company Employees...</description>
         <copyright>Copyright 2008 - 2010</copyright>
         <item>
                  <title>John Doe</title>
                  <description>Main Street</description>
                  <link>http://localhost/RSSFeeds/EmployeeDetails.aspx?EmpId=1</link>
                  <pubDate>9/22/2008 1:43:48 PM</pubDate>
         </item>
         <item>
                  <title>Jane Doe</title>
                  <description>First Street</description>
                  <link>http://localhost/RSSFeeds/EmployeeDetails.aspx?EmpId=2</link>
                  <pubDate>9/22/2008 1:43:48 PM</pubDate>
         </item>
         <item>
                  <title>Andrew Doe</title>
                  <description>Downtown</description>
                  <link>http://localhost/RSSFeeds/EmployeeDetails.aspx?EmpId=3</link>
                  <pubDate>9/22/2008 1:43:48 PM</pubDate>
         </item>
     </channel>
</rss>

Available RSS Readers

Instead of developing a custom RSS Reader, you can use a number of readers already available on the internet. Some of these are SharpReader, BitsCast, BlogBridge, NewsGator, NetNewsWire, Mozilla, FeedDemon, RssBandit, Shrook, Feedreader, etc.

RSS feed publishing

This sample application is about publishing SQL Server 2005 table data as a custom RSS feed over the internet.

SQL Server 2005 Database
To begin with, let us create a database in SQL Server 2005 with name RSSDB. In RSSDB, create a table with name tblEmployees, having the design as shown in Figure I.

Provide default as 0 to the Emp_IsDeleted column.

Table Employee
Image 1. Design of Employee table

Enter some data into the tblEmployees table as follows:

Employee Data
Image 2. Employee table filled with some data

SQL Server 2005 Stored Procedure

Create a new SQL Server stored procedure called GetEmployees. To do this, open a SQL Server 2005 query window, then paste and execute the following:

CREATE PROCEDURE [dbo].[GetEmployees]
AS
BEGIN

         SELECT * FROM tblEmployees
END

ASP.NET 2.0

  1. Open Microsoft Visual Studio 2005 and create a 'Web Site' with name RSSFeeds. After the project is created, right click on the project node and click on 'Add New Item'.

  2. In the 'Add New Item' dialog box, select 'Web Form' and enter the name EmployeeDetails.aspx in the 'Name' area and click on Add.

  3. Create a new web.config file and inside the <configuration></configuration> section enter the following:

    <connectionStrings>
            <add name="SQLEmployee" connectionString="Data Source={server name};DataBase=RSSDB;User Id=JavaUser; Password=*****;"/>
    </connectionStrings>

  4. Open the 'Source' view of EmployeeDetails.aspx.

  5. After the first line of <%@ Page %> directive, add the following:

     <%@ OutputCache Duration="120" %>

While creating a dynamic RSS feed, a problem may creep in while the user provides different parameter names like, EmpId to the RSS feed url. It may happen that when the user tries to view the output with a different EmpId, the output that is shown is the old one. It happens as the previous cached page is retrieved. To work around this problem, VaryByParam is used to tell the cache that the output varies based on this parameter value (EmpId) and a new cache needs to be created based on the EmpId value passed. In that case, instead of the previous statement, include the line as follows:

<%@ OutputCache Duration="120" VaryByParam="EmpId" %>

  1. Open the EmployeeDetails.aspx.cs page.

  2. Inside the Page_Load function, enter the following block:

     if (!Page.IsPostBack)
     {}

  1. Inside the Page.IsPostBack block, enter the following lines of code:

     // Clear the response buffer contents
     Response.Clear();
     Response.ContentType = "text/xml";
     XmlTextWriter xmlRSSFeed = new XmlTextWriter(Response.OutputStream, Encoding.UTF8);

     // Start writing the rss tags
     xmlRSSFeed.WriteStartDocument();
     xmlRSSFeed.WriteStartElement("rss");
     xmlRSSFeed.WriteAttributeString("version", "2.0");
     xmlRSSFeed.WriteStartElement("channel");
     xmlRSSFeed.WriteElementString("title", "Employee Details");
     xmlRSSFeed.WriteElementString("link", "http://localhost/RSSFeeds");
     xmlRSSFeed.WriteElementString("description", "Details of all Company Employees...");
     xmlRSSFeed.WriteElementString("copyright", "Copyright 2008 - 2010");

     // Objects needed for connecting to the SQL database
     SqlConnection sqlCon;
     SqlCommand sqlCmd;
     SqlDataReader sqlDr;

     // Call SQL Server stored procedure
     sqlCon = new SqlConnection(ConfigurationManager.ConnectionStrings["SQLEmployee"].ToString());
     sqlCmd = new SqlCommand("GetEmployees", sqlCon);
     sqlCmd.CommandType = CommandType.StoredProcedure;

     sqlCon.Open();

     sqlDr = sqlCmd.ExecuteReader();

     // Loop through the content of the database and add them to the RSS feed
     while (sqlDr.Read())
     {
         xmlRSSFeed.WriteStartElement("item");
         xmlRSSFeed.WriteElementString("title", sqlDr["Emp_FirstName"].ToString() + " " + 
                                                      sqlDr["Emp_LastName"].ToString());
         xmlRSSFeed.WriteElementString("description", sqlDr["Emp_Address"].ToString());
         xmlRSSFeed.WriteElementString("link", "http://localhost/RSSFeeds/EmployeeDetails.aspx?EmpID=" +
                                                                       sqlDr["Emp_Id"]);
         xmlRSSFeed.WriteElementString("pubDate", DateTime.Now.ToString());
         xmlRSSFeed.WriteEndElement();

     }
     sqlDr.Close();
     sqlCon.Close();

     // Close all tags
     xmlRSSFeed.WriteEndElement();
     xmlRSSFeed.WriteEndElement();
     xmlRSSFeed.WriteEndDocument();
     xmlRSSFeed.Flush();
     xmlRSSFeed.Close();
     Response.End();

  1. Right-click EmployeeDetails.aspx and click on 'Set as Start Page'.

  2. Run the project from inside Visual Studio 2005.

RSS feed reader

A custom RSS Feed Reader can be developed in ASP.NET 2.0 targeting the feed: http://localhost/RSSFeeds/EmployeeDetails.aspx

ASP.NET 2.0

  1. Open Microsoft Visual Studio 2005 and create a 'Web Site' with name RSSFeedReader. After the project is created, right click on the project node and click on 'Add New Item'.

  2. In the 'Add New Item' dialog box, select 'Web Form' and enter the name RSSRead.aspx in the 'Name' area and click on Add.

  3. Open the 'Source' view of RSSRead.aspx.

  4. Inside the <form> tag of RSSRead.aspx document, include the following html:

     <table cellpadding="0" cellspacing="0">
         <tr>
             <td>
                 <table class="NormalText" runat="server" id="tblNews" cellpadding="0" cellspacing="0">
                 </table>
             </td>
         </tr>
     </table>

  1. Open RSSRead.aspx.cs.

  2. Include the following using statements at the top of the file:

    using System.Net;
    using System.Xml;
    using System.IO;

  3. Create a method as follows inside the document:

     public void ProcessRSSItem(string rssURL)
     {
          // Read the RSS feed
          WebRequest myRequest = WebRequest.Create(rssURL);
          WebResponse myResponse = myRequest.GetResponse();

          Stream rssStream = myResponse.GetResponseStream();

          // Load a XML Document
          XmlDocument rssDoc = new XmlDocument();
          rssDoc.Load(rssStream);

          XmlNodeList rssItems = rssDoc.SelectNodes("rss/channel/item");

          string title = "";
          string link = "";
          string description = "";

          // Loop through RSS Feed items
          for (int i = 0; i < rssItems.Count; i++)
          {
               XmlNode rssDetail;

               rssDetail = rssItems.Item(i).SelectSingleNode("title");
               if (rssDetail != null)
               {
                     title = rssDetail.InnerText;
               }
               else
               {
                     title = "";
               }

               rssDetail = rssItems.Item(i).SelectSingleNode("link");
               if (rssDetail != null)
               {
                     link = rssDetail.InnerText;
               }
               else
               {
                     link = "";
               }

               rssDetail = rssItems.Item(i).SelectSingleNode("description");
               if (rssDetail != null)
               {
                     description = rssDetail.InnerText;
               }
               else
               {
                     description = "";
               }

               // Populate the HTML table rows and cells
               HtmlTableCell cell1 = new HtmlTableCell();
               cell1.InnerHtml = "<b><a href='" + link + "' target='new'>" + title + "</a></b>";
               HtmlTableRow tr1 = new HtmlTableRow();
               tr1.Cells.Add(cell1);
               tblNews.Rows.Add(tr1);
               HtmlTableCell cell2 = new HtmlTableCell();
               cell2.InnerHtml = "<p align='justify'>" + description + "</p>";
               HtmlTableRow tr2 = new HtmlTableRow();
               tr2.Cells.Add(cell2);
               tblNews.Rows.Add(tr2);
          }
     }

  1. Inside the Page_Load method, write the following code to call the ProcessRSSItem method:

     string rssURL = "http://localhost/RSSFeeds/EmployeeDetails.aspx".ToString();
     try
     {
          ProcessRSSItem(rssURL);
     }
     catch (Exception ex)
     {
     }

  1. Right-click RSSRead.aspx and click on 'Set as Start Page'.

  2. Run the project from inside Visual Studio 2005 and enjoy new feature. Happy Programming!


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