How to Load XML Documents in ASP.NET 2.0

The next picture shows you the Object Browser showing the XMLDocument class in the System.XML namespace. The XMLDocument class inherits from the XMLNode class as in the following hierarchical relationship:

System.Object
   System.Xml.XmlNode
     System.Xml.XmlDocument

The XMLDocument class has a large number of Public/Private properties and methods shown in the picture, which are also from the object browser in the Visual Studio 2.0 IDE. This class can invoke its methods not only to load XML documents but also create XML documents with all the different element types you would find in an XML document. This article however will look only at loading the XML document. We will assume it exists as an xml file on the hard drive of the machine; or is available as a file that can be accessed as an URL; or that the content is available as a string.

Loading an XMLDocument

The five different Load() methods shown in the above picture surrounded by a red rectangle will be explored with code to show how each of them may be used to load the XMLDocument. The various methods are used in a web site project, XMLSite. The XMLDocument gets instantiated and loaded in the click event of a button. All of the examples use the same XML file which has been used in other XML related tutorials by the author on the DevArticles.com and ASPFree.com web sites.

LoadXml (string) method

After instantiating an XMLDocument using the New keyword you can invoke the LoadXml() method with the XML file in a string format as an argument as shown in the following picture. Also observe that the argument to the method typed in is an XML file content in a string format.

Once the XML document is loaded you can invoke its properties through the XML DOM Model to verify if the content is loaded correctly. This may be simply tested as shown by the completed code and the output written as a Response.Write() as shown.

Response.Write(xmldoc.HasChildNodes)
Response.Write("<br/>")
Response.Write(xmldoc.DocumentElement.LastChild.InnerXml)
Response.Write("<br/>")

The result of running the above in the IE browser is as shown in the next picture.

Load (string) where string is an XML file

The Load (string) method takes as an argument the reference to an XML file located in the file system as shown in the following code.

Imports system.xml
Partial Class LoadString
   Inherits System.Web.UI.Page

   Protected Sub Button1_Click(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Button1.Click
   Dim xmldoc As New XmlDocument
   xmldoc.Load("C:Inetpubwwwrootwebstudents.xml")
   Response.Write("Loaded as an xml file located on the C drive<br/>")
   Response.Write("Does the document has child nodes? " _
   & "<b>" & xmldoc.HasChildNodes & "</b>")
   Response.Write("<br/>")
   Response.Write("What is the Last child? " & "<b>" _ 
   & xmldoc.DocumentElement.LastChild.InnerXml & "</b>")
   Response.Write("<br/>")
   Response.Write("What is Last child's Last child? " & _
   "<b>" & xmldoc.DocumentElement.LastChild.LastChild.InnerXml _
   & "</b>")
   End Sub
End Class

Again the DOM API is used to look at the Last child and the Last child's Last child as in the code. The browser display for this is shown in the next picture.

Load (System.IO.TextReader) method

The next picture shows the System.IO.TextReader class. The Read() method of this will be invoked to load the xml as in the code.

Imports System.xml
Partial Class LoadWithTextReader
   Inherits System.Web.UI.Page

   Protected Sub Button1_Click(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Button1.Click

     Dim docxml As New XmlDocument

     Dim rdr As New XmlTextReader( _
     "http://localhost/webstudents.xml")
     rdr.Read()
     docxml.Load(rdr)
     Response.Write("What is the Last Child? " & "<b>" & _
     docxml.DocumentElement.LastChild.InnerXml & "</b>")
   End Sub
End Class

Again the DOM API is used to look at the Last child as in the code. The browser display for this is shown in the next picture. Although a URL is passed as an argument, you may also pass a file reference as in the Load (string) method discussed earlier.

It may be noted that the StreamReader class can also be used to read the XML from the file as a text  from its Read() method since the StreamReader inherits from the System.IO.TextReader as shown in the next picture.

Load (System.IO.Stream) method

The class FileStream inherits from System.IO.Stream as shown in the next picture. This is utilized to read the file from the drive as shown in the code that follows.

Imports System.xml
Partial Class LoadStream
   Inherits System.Web.UI.Page

   Protected Sub Button1_Click(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Button1.Click
     Dim xmldoc As New XmlDocument
     Dim fs As New IO.FileStream( _
     "C:Inetpubwwwrootwebstudents.xml", _
     IO.FileMode.Open, IO.FileAccess.Read)
     xmldoc.Load(fs)
     Response.Write(xmldoc.HasChildNodes)
     Response.Write("<br/>")
     Response.Write("What is the Last Child? " & "<b>" & _
     xmldoc.DocumentElement.LastChild.InnerXml & "</b>")
   End Sub
End Class

Again the DOM API is used to look at the Last child as in the code. The browser display for this is shown in the next picture. Although a file reference is passed as an argument, you may also pass a URL reference as in the Load (string) method discussed earlier.

Load (System.XML.XMLReader) method

The XMLReader is the API for parsing, and XMLTextReader, which inherits from the XMLReader, can be used for reading text or bytes.

Imports System.xml
Partial Class LoadXMLReader
   Inherits System.Web.UI.Page

   Protected Sub Button1_Click(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Button1.Click
     Dim xmldoc As New XmlDocument
     Dim xmlrdr As New XmlTextReader( _
     "http://localhost/webstudents.xml")
     xmldoc.Load(xmlrdr)
     Response.Write(xmldoc.HasChildNodes)
     Response.Write("<br/>")
     Response.Write("What is the Last Child? " & "<b>" & _
     xmldoc.DocumentElement.LastChild.InnerXml & "</b>")
   End Sub
End Class

Again the DOM API is used to look at the Last Child as in the code. The browser display for this is shown in the next picture. Although a URL reference is passed as an argument, you may also pass a File reference as in the Load (string) method discussed earlier.

Summary

This tutorial has shown with examples the several ways in which an XML document can be loaded. Once loaded it can be parsed, or utilized in several ways. All of the examples take the same webstudents.xml file used in several other tutorials. The examples are provided with ample reference to the various classes and the namespaces and should provide an appropriate starting point for those venturing into XML using VS 2005.