Home > Articles > Web Services > XML

Like this article? We recommend 

Like this article? We recommend

Sams Teach Yourself XML in 24 Hours, Complete Starter Kit, 3rd EditionSams Teach Yourself XML in 24 Hours, Complete Starter Kit, 3rd Edition

Learn More Buy

Like this article? We recommend

Like this article? We recommend 

Sams Teach Yourself XML in 24 Hours, Complete Starter Kit, 3rd EditionSams Teach Yourself XML in 24 Hours, Complete Starter Kit, 3rd Edition

Learn More Buy

The Solution

The core component of the solution (the complete source is available here) is the OutputXMLResponse subroutine shown in Listing 1, which checks for the presence of the XML cookie with the UseXMLOutput function, outputting an XML document if the cookie is set, or the transformed HTML markup if the cookie is not present. The parameters to this function are an XML document parsed in a DOM tree (XDoc) and the relative path to the XSLT style sheet (StyleURL).

NOTE

The code examples in the article use Microsoft XML (MSXML) with ASP. PHP DOM processing is very similar.

Listing 1 Main output function.

Sub OutputXMLResponse(XDoc,StyleURL)
 Dim XSLT,HText

 If UseXMLOutput Or IsNull(StyleURL) Then
  OutputXMLDocument XDoc,StyleURL
 Else
  HText = LocalXSLTransform(XDoc,StyleURL)
  OutputUTFtext HText, "text/html"
 End If
End Sub

The UseXMLOutput function, shown in Listing 2, checks for the presence of the XML cookie. Due to incomplete support of XSLT in Internet Explorer 5, it always returns False if the user agent is IE5.

Listing 2 Select XML or HTML response.

Function UseXMLOutput
 UseXMLOutput = False
 If InStr(Request ("HTTP_USER_AGENT"),"MSIE 5") > 0 Then Exit Function
 UseXMLOutput = Request.Cookies("XML") = "1"
End Function

The OutputXMLDocument subroutine in Listing 3 is conceptually simple: It prepends the xml-stylesheet processing directive in front of the XML root element, and outputs the value of the xml property of the DOM document by using the OutputUTFtext function. A minor adjustment is needed to ensure that the <?xml ?> processing instruction is always present in the output XML stream; see the source code for the complete subroutine.

NOTE

The PHP equivalent for the xml property is the DomDocument->dump_mem method.

Listing 3 Send XML text to the client.

Sub OutputXMLDocument(XDoc,StyleURL)
 Dim XPI
 If StyleURL <> "" Then
  Set XPI = XDoc.createProcessingInstruction("xml-stylesheet", "href=’" & StyleURL & "’ type=’text/xsl’")
  XDoc.insertBefore XPI, XDoc.firstChild.nextSibling
 End If
 OutputUTFtext XDoc.xml,"text/xml"
End Sub

When the XML cookie is not set, the LocalXSLTransform function in Listing 4 performs the XSLT transformation. It creates a new DOM document, loads the XSL style sheet into it, and uses the style sheet to transform the input DOM document. You could also enhance its performance with server-cached XSLT processors.

NOTE

Several options are set on the input XML document and the XSL style sheet with the SetXMLOptions subroutine to enable the use of the <xsl:import> tag and the XSL document() function.

Listing 4 Perform local XSLT transformation.

Function LocalXSLTransform(XDoc,StyleURL)
 Dim XSLT
 Set XSLT = Server.CreateObject(DOMClass)
 SetXMLOptions XDoc : SetXMLOptions XSLT
 If Not XSLT.Load (Server.MapPath(StyleURL)) Then RaiseError "XSL stylesheet load failed " & StyleURL
 If XSLT.parseError.errorCode <> 0 Then RaiseError "XML parsing failed: " & XSLT.parseError.reason
 LocalXSLTransform = XDoc.transformNode(XSLT)
End Function

Sub SetXMLOptions (XD)
 XD.Async = False
 XD.setProperty "ServerHTTPRequest",true
 XD.setProperty "AllowDocumentFunction",true
End Sub

Sub RaiseError(Txt)
 Err.Raise vbObjectError+1, "XML library",Txt
End Sub

Finally, the OutputUTFtext function in Listing 5 returns the XML text string or HTML markup to the client. This function clears the output buffer (to erase any previous debugging messages or HTML markup embedded in the script), sets the content-type header, changes the codepage property to a UTF-8 code page, displays the input result text, and stops response processing.

NOTE

The HTML markup produced by the local XSLT transformation doesn’t include the META http-equiv=content-type tag, to prevent the mismatch between the HTTP response header and the META tag. The source code for the LocalXSLTransform function includes a fix for a bug related to META tags in MSXML version 4.0.

Listing 5 Output UTF-8 text to the client.

Sub OutputUTFtext (txt,contentType)
 Response.Clear
 Response.ContentType = contentType
 Response.Charset = "utf-8"
 Response.Codepage = 65001
 Response.Write txt
 Response.End
End Sub

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.