XML File Parsing in VB.NET

Introduction

Parsing XML files has always been time consuming and sometimes tricky. .NET framework provides powerful new ways of parsing XML. The various techniques know to parse xml files with .NET framework are using XmlTextReader, XmlDocument, XmlSerializer, DataSet and XpathDocument. I will explore the XmlTextReader and XmlDocument approach here.

The Xml File

Figure 1 outlines the xml file that will be parsed.

<?xml version="1.0" encoding="UTF-8"?>
<family>
  <name gender="Male">
    <firstname>Tom</firstname>
    <lastname>Smith</lastname>
  </name>
  <name gender="Female">
    <firstname>Dale</firstname>
    <lastname>Smith</lastname>
  </name>
</family>

Figure1: Xml file

Parsing XML with XMLTextReader

Using XmlTextReader is appropriate when the structure of the XML file is relatively simple. Parsing with XmlTextReader gives you a pre .net feel as you sequentially walk through the file using Read() and get data using GetAttribute() andReadElementString() methods. Thus while using XmlTextReader it is up to the developer to keep track where he is in the Xml file and Read() correctly. Figure 2 below outlines parsing of xml file with XmlTextReader

Imports System.IO
Imports System.Xml
Module ParsingUsingXmlTextReader
Sub Main()
  Dim m_xmlr As XmlTextReader
  'Create the XML Reader

  m_xmlr = New XmlTextReader("C:\Personal\family.xml")
  'Disable whitespace so that you don't have to read over whitespaces

  m_xmlr.WhiteSpaceHandling = WhiteSpaceHandling.NONE
  'read the xml declaration and advance to family tag

  m_xmlr.Read()
  'read the family tag

  m_xmlr.Read()
  'Load the Loop

  While Not m_xmlr.EOF
    'Go to the name tag

    m_xmlr.Read()
    'if not start element exit while loop

    If Not m_xmlr.IsStartElement() Then
      Exit While
    End If
    'Get the Gender Attribute Value

    Dim genderAttribute = m_xmlr.GetAttribute("gender")
    'Read elements firstname and lastname

    m_xmlr.Read()
    'Get the firstName Element Value

    Dim firstNameValue = m_xmlr.ReadElementString("firstname")
    'Get the lastName Element Value

    Dim lastNameValue = m_xmlr.ReadElementString("lastname")
    'Write Result to the Console

    Console.WriteLine("Gender: " & genderAttribute _
      & " FirstName: " & firstNameValue & " LastName: " _
      & lastNameValue)
    Console.Write(vbCrLf)
  End While
  'close the reader

  m_xmlr.Close()
End Sub
End Module

Figure 2: Xml Parsing with XmlTextReader

Parsing XML with XmlDocument

The XmlDocument class is modeled based on Document Object Model. XmlDocument class is appropriate if you need to extract data in a non-sequential manner. Figure 3 below outlines parsing of xml file with XmlDocument

Imports System.IO
Imports System.Xml
Module ParsingUsingXmlDocument
Sub Main()
  Try
    Dim m_xmld As XmlDocument
    Dim m_nodelist As XmlNodeList
    Dim m_node As XmlNode
    'Create the XML Document

    m_xmld = New XmlDocument()
    'Load the Xml file

    m_xmld.Load("C:\CMS\Personal\family.xml")
    'Get the list of name nodes 

    m_nodelist = m_xmld.SelectNodes("/family/name")
    'Loop through the nodes

    For Each m_node In m_nodelist
      'Get the Gender Attribute Value

      Dim genderAttribute = m_node.Attributes.GetNamedItem("gender").Value
      'Get the firstName Element Value

      Dim firstNameValue = m_node.ChildNodes.Item(0).InnerText
      'Get the lastName Element Value

      Dim lastNameValue = m_node.ChildNodes.Item(1).InnerText
      'Write Result to the Console

      Console.Write("Gender: " & genderAttribute _
        & " FirstName: " & firstNameValue & " LastName: " _
        & lastNameValue)
      Console.Write(vbCrLf)
    Next
  Catch errorVariable As Exception
    'Error trapping

    Console.Write(errorVariable.ToString())
  End Try
End Sub
End Module

Figure 3: Xml Parsing with XmlDocument

Compilation and Result

Make sure you have vbc.exe in your path. From the command prompt go to C:\Personal>. Compile ParsingUsingXmlTextReader.vb and ParsingUsingXmlDocument.vb.

C:\Personal>vbc /out:ParsingUsingXmlTextReadervb.exe ParsingUsingXmlTextReader.vb
C:\Personal>vbc /out:ParsingUsingXmlDocumentvb.exe ParsingUsingXmlDocument.vb

When you run the individual program

C:\Personal>ParsingUsingXmlTextReadervb.exe 

OR

C:\Personal>ParsingUsingXmlDocumentvb.exe

You will see the following result for both

Gender: Male FirstName: Tom LastName: Smith

Gender: Female FirstName: Dale LastName: Smith

Conclusion

There are different ways to parse XML files and the best method depends on your situation and the programming style preferred.