實例簡析XPath串函數和XSLT

XPath(xml Path language)是一種處理XML文檔段的語言。 XSLT(Extensible Stylesheet Language Transformations,可擴充樣式表語言轉換)使用XPath描述表達式和位址路徑控制節點選取。 XSLT可以將XML轉換為各種格式，如HTML或其他格式。 
    以下用一個郵件合併程序簡單說明XPath的字串函數。下面的XML檔案中包含數據，XSLT檔案中包含對郵件格式的定義。 MSXML4.0對XML文件套用樣式表，產生一個合併的郵件文字文件。
XML檔Letter.xml

<?xml version="1.0" encoding="UTF-8"?>
<Letter>
  <Date>July 17, 2002</Date>
  <To>
     <FirstName>Vicky</FirstName>
     <LastName>P</LastName>
     <Sex>Male</Sex>
  </To>
  <Address>
     <Line1>900 National Pkwy</Line1>
     <Line2>Suite 105</Line2>
     <City>Bellevue</City>
     <State>WA</State>
     <Zip>98007</Zip>
     <Country>USA</Country>
  </Address>
  <Subject>ESTATE OF JOHN DOE / FILE NO. 12345.6789</Subject>
  <Text>
     Please pay the PRoperty taxes as soon as possible.
  </Text>
  <Sender>
     <FirstName>John</FirstName>
     <LastName>M</LastName>
     <Title>Sr. Tax Consultant</Title>
  </Sender>
</Letter>

XSLT樣式表文件Letter.xsl

<?xml version=&#39;1.0&#39; encoding="utf-8"?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" indent="yes"/>
<xsl:variable name="NL" select="&#39;&#xA;&#39;" />
<xsl:variable name="Para" select="concat($NL, $NL)" />
<xsl:template match="/">
   <xsl:value-of select="//Date" />
   <xsl:value-of select="$Para" />
To,
<xsl:value-of select="concat(//To/FirstName, &#39; &#39;, //To/LastName)" />
<xsl:value-of select="$NL" />
<xsl:value-of select="//Address/Line1" />
<xsl:value-of select="$NL" />
<xsl:value-of select="//Address/Line2" />
<xsl:value-of select="$NL" />
<xsl:value-of select="concat(//Address/City, &#39; &#39;, //Address/State, &#39; &#39;, //Address/Zip)" />
<xsl:value-of select="$NL" />
<xsl:value-of select="//Address/Country" />
<xsl:value-of select="$Para" />
Regarding: <xsl:value-of select="//Subject" />
<xsl:value-of select="$NL" />
Dear <xsl:if test="starts-with(//Sex, &#39;M&#39;)">Mr. </xsl:if><xsl:if test="starts-with(//Sex, &#39;F&#39;)">Miss </xsl:if>
<xsl:value-of select="concat(//To/FirstName, &#39; &#39;, //To/LastName)" />,
<xsl:value-of select="$Para" />
<xsl:value-of select="//Text" />
<xsl:value-of select="$Para" />
Sincerely,
<xsl:value-of select="$Para" />
<xsl:value-of select="concat(//Sender/FirstName, &#39; &#39;, //Sender/LastName)" />
<xsl:value-of select="$NL" />
<xsl:value-of select="//Sender/Title" />
</xsl:template>
</xsl:stylesheet>

上面的樣式表舉例說明了concat和starts-with XPath字串函數和怎樣在輸出文字中增加新行，還有定義和使用變數。
    以下是程式的執行結果。

1.VC6建立Win32控制台應用程式。
2.在stdafx.h中加入下面的程式碼：

#include <TCHAR.H>
#include <stdio.h>
#include <time.h>
#import "msxml4.dll"
// If this import statement fails, you need to install MSXML 4.0 SP1 from:
//http://msdn.microsoft.com/downloads/sample.asp?url=/MSDN-FILES/027/001/766/msdncompositedoc.xml
#include <msxml2.h>
// If this include statement fails, you need to install MSXML 4.0 SP1 SDK from:
//http://msdn.microsoft.com/downloads/sample.asp?url=/MSDN-FILES/027/001/766/msdncompositedoc.xml
// You also need to add the include file and library search path
// to Visual C++&#39;s list of directories (Tools > Options... > Directories).
using namespace MSXML2;
inline void EVAL_HR( HRESULT _hr ) 
   { if FAILED(_hr) throw(_hr); }
#define TEMP_SIZE  _MAX_PATH               // size of short buffer
static _TCHAR   szTemp[TEMP_SIZE];         // multipurpose buffer on stack
static DWord    dwLen;

3.上面的程式碼引入MSXML4類型庫，包含MSXML頭文件，檢查HRESULT值並聲明了一些全域變數。
4.main函數：

  int main(int argc, char* argv[])
{
 try
 {
  EVAL_HR(CoInitialize(NULL));
  // Make sure that MSXML 4.0 is installed
  if (!isMSXMLInstalled())
   return -1;
  // Make sure that XML and XSL file names are passed
  // as command line parameters
  if (argc < 3)
   // Show proper message here
   return -1;
  
  IXMLDOMDocument2Ptr pXMLDoc = NULL;
  IXMLDOMDocument2Ptr pXSLDoc = NULL;
  
  // Load the XML document
  if (loadDocument(pXMLDoc, argv[1], true))
  {
   // Load the stylesheet
   if (loadDocument(pXSLDoc, argv[2], false))
   {
    _ftprintf(stdout, pXMLDoc->transformNode(pXSLDoc));
   }
   else
   {
    printMSXMLError(pXSLDoc);
   }
  }
  else
  {
   printMSXMLError(pXMLDoc);
  }
 }
 catch(...)
 {//exception handling
 }
 
 _ftprintf(stdout, "\n\nPress Enter to continue...");
 getchar();
 CoUninitialize();
 return 0;
}

5.XML檔案和XSLT樣式表檔案名稱作為命令列參數傳遞給應用程式。主函數透過呼叫isMSXMLInstalled驗證    MSXML4.0是否安裝。接下來兩次呼叫loadDocument;先是載入XML文檔,然後是載入XSLT樣式表。 最後呼叫transformNode進行轉換。

6.本範例程式碼下載：http://www.perfectxml.com/CPPMSXML/downloads/20020716MailMerge.zip

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