HOW TO: Locate and Replace Special Characters in an XML File with Visual Basic .NET (308060)

SUMMARY

This article describes how to replace special characters in an Extensible Markup Language (XML) file by using Visual Basic .NET.

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Description of the Technique

XML predefines the following five entity references for special characters that would otherwise be interpreted as part of markup language:

Character Name	Entity Reference	Character Reference	Numeric Reference
Ampersand	&	&	&
Left angle bracket	&lt;	<	&#38;#60;
Right angle bracket	&gt;	>	&#62;
Straight quotation mark	&quot;	"	&#39;
Apostrophe	&apos;	'	&#34;

You can use entity and character references to escape the left angle bracket, the ampersand, and other delimiters. You can also use numeric character references; they are expanded immediately when they are recognized and they are treated as character data, so you can use the numeric character references

If you are declaring either of the following two entities

• lt
• amp

you have to declare them as internal entities whose replacement text is a character reference to the respective character (the left angle bracket or the ampersand) that is being escaped; the double escaping is required for these entities so that references to them produce a well-formed result.

If you are declaring any of the following three entities

• gt
• apos
• quot

you have to declare them as internal entities whose replacement text is the single character being escaped.

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Determine Whether a Special Character Replacement Is Required

Not Required: XML Files in Which the Data Is Retrieved from a Database

When you are using the Microsoft .NET Framework, data is retrieved and stored in a DataSet. When you are writing data from a DataSet to an XML file by using the WriteXml method, the special characters that are referred to in the "Summary" section are replaced with the respective character references; therefore, when you are writing XML files and you are using a DataSet, no special replacement process is required.

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Required: An XML File with Special Characters

Sometimes the XML file or the XML data that is coming from a third party may use these special characters; in this scenario, the data generates errors when you load it into an XmlDocument object or an XmlReader object.

The following error is generated when the ampersand character is encountered: where line # and position # represent the exact position of the special character.

The following error occurs when a left angle bracket is encountered: In this error message, the line # and position # do not indicate the position where the left angle bracket exists, but where the second left angle bracket is encountered.

If the XML file contains a right angle bracket (>), a straight quotation mark (") or an apostrophe ('), these are handled by the XmlReader and the XmlDocument objects because only single character replacement is required for these characters.

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Replace the Special Characters

To replace the ampersand and the left angle bracket characters:

1. Create the XML file.
2. Create the Visual Basic .NET application, and then insert the code.

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Create the XML File

Copy and paste the following code into Notepad, and then save the file as customers.xml:

<?xml version="1.0" standalone="yes"?>
<Customers>
<Customer>
<CustomerID>BLAUS</CustomerID>
<CompanyName>Blauer See Delikatessen</CompanyName>
<ContactName>Hanna Moos</ContactName>
<Region>test<ing</Region>
</Customer>
<Customer>
<CustomerID>SPLIR</CustomerID>
<CompanyName>Split Rail Beer & Ale</CompanyName>
<ContactName>Art raunschweiger</ContactName>
<Region>WY</Region>
</Customer>
</Customers>
				

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Create Visual Basic .NET Project

1. Create a new Visual Basic .NET Windows application.
2. Use a drag-and-drop operation to move a TextBox, two Button controls, and a DataGrid.
3. Set the Multiline property of the TextBox to True.
4. Import the following namespaces:

   Imports System.Xml
   Imports System.IO
   Imports System.Data.SqlClient
   					

5. After the following section

   Inherits System.Windows.Forms.Form

   copy and paste the following code sample:

    Dim filepath As String = "C:\customers.xml"
   Private Sub ReplaceSpecialChars(ByVal linenumber As Long)
           Dim strm As StreamReader
           Dim strline As String
           Dim strreplace As String
   
           Dim tempfile As String = "C:\temp.xml"
           Try
               FileCopy(filepath, tempfile)
           Catch ex As Exception
               MessageBox.Show(ex.Message)
           End Try
   
           Dim strmwriter As New StreamWriter(filepath)
           strmwriter.AutoFlush = True
   
           strm = New StreamReader(tempfile)
   
   
           Dim i As Long = 0
           While i < linenumber - 1
               strline = strm.ReadLine
               strmwriter.WriteLine(strline)
               i = i + 1
           End While
   
           strline = strm.ReadLine
           Dim lineposition As Int32
           lineposition = InStr(strline, "&")
           If lineposition > 0 Then
               strreplace = "&amp;"
           Else
               lineposition = InStr(2, strline, "<")
               If lineposition > 0 Then
                   strreplace = "<"
               End If
           End If
           strline = Mid(strline, 1, lineposition - 1) + strreplace + Mid(strline, lineposition + 1)
           strmwriter.WriteLine(strline)
   
           strline = strm.ReadToEnd
           strmwriter.WriteLine(strline)
   
           strm.Close()
           strm = Nothing
   
           strmwriter.Flush()
           strmwriter.Close()
           strmwriter = Nothing
   
       End Sub
   
       Public Function LoadXMLDoc() As XmlDocument
           Dim xdoc As XmlDocument
           Dim lnum As Long
           Dim pos As Long
           Dim Newxml As String
           Try
               xdoc = New XmlDocument()
               xdoc.Load(filepath)
           Catch ex As XmlException
               MessageBox.Show(ex.Message)
               lnum = ex.LineNumber
               ReplaceSpecialChars(lnum)
   
               xdoc = LoadXMLDoc()
   
           End Try
           Return (xdoc)
       End Function
   					

6. Copy and paste the following code into the Click event of Button1:

   Dim xmldoc As New XmlDocument()
           xmldoc = LoadXMLDoc()
           Dim nextnode As XmlNode
           nextnode = xmldoc.FirstChild.NextSibling
           TextBox1.Text = nextnode.OuterXml
   					

7. Copy and paste the following code into the Click event of Button2:

   Dim ds As New DataSet()
           Dim xdoc As New XmlDocument()
           Dim cnNwind As New SqlConnection("Data source=myservername;user id=myuser;Password=mypassword;Initial catalog=Northwind;")
           Dim daCustomers As New SqlDataAdapter("Select customerid,companyname,contactname, region from customers where region='WY'", cnNwind)
           Dim filepath As String
           Try
               daCustomers.Fill(ds, "Customers")
               DataGrid1.DataSource = ds.Tables(0)
               ds.WriteXml("C:\Dataset.xml")
               xdoc.Load("C:\Dataset.xml")
               Dim nextnode As XmlNode
               nextnode = xdoc.FirstChild.NextSibling
               TextBox1.Text = nextnode.OuterXml.ToString
           Catch ex As Exception
               MessageBox.Show(ex.Message)
           End Try
   					

8. Change the server name, the user name, and the password to connect to your server that is running Microsoft SQL Server.
9. Build the project, and then run it.
10. Click Button1.
    
    The errors that you receive are consistent with the description of the errors that are explained in the "Required: An XML File with Special Characters" section. The XML data is then displayed in the TextBox; the ampersand is replaced with
11. Click Button2.
    
    In the DataGrid, companyname has an ampersand and the TextBox shows the XML data with

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