XML Validation with XSLT & Calling Custom functions from XSLT

Surya Prakash
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In this article, I will discuss about validating XML against defined XSL. Prior to getting into this article, it's mandatory that one should have basic knowledge on what XML & XSL are.

Consider the below XML as input (UserCheck.xml) to our application

<?xml version="1.0" encoding="utf-16"?>
<root xmlns:func="urn:actl-xslt">
<User>
<UserName>suryaprakash</UserName>
<Password>password</Password>
</User>
</root>

This example describes the below business rules:

If UserName, Password node not exists, generate XML ERROR as output
If UserName, Password nodes are empty, generate XML ERROR as output
Check if user,password exists in DB or not & generate XML SUCCESS or ERROR as output

The output would be as follows if there are any errors, which will be inserted into an XML file (result.xml)

Each ERROR tag would represent each error with ERRORMSG & ERRORCODE

<root xmlns:msxsl="urn:schemas-microsoft-com:xslt" xmlns:func="urn:actl-xslt">
<OUTPUT>
    <ERROR>
      <ErrorMsg>
        UserName Node Contains Invalid Data
      </ErrorMsg>
      <ErrorCode>
        ERR_003
      </ErrorCode>
    </ERROR>
</OUTPUT>
</root>

Let get into the sample with below steps

Step 1: Define XML
Step 2: Define XSL as per our business rules defined above
Step 3: Define function which will be called from XSL
Step 4: Implement code validate XML with XSL as follows which will be called from XSL

Step 1: Define XML

Consider the below XML as input to our example

<?xml version="1.0" encoding="utf-16"?>
<root xmlns:func="urn:actl-xslt">
<User>
<UserName>suryaprakash</UserName>
<Password>password</Password>
</User>
</root>

Step 2: Define XSL as per our business rules defined above

<?xml version="1.0"?>
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt"
xmlns:func="urn:actl-xslt">
<xsl:template match="root">
    <root>
      <xsl:for-each select="User">
        <OUTPUT>
          <xsl:if test="not(UserName)">
            <ERROR>
              <ErrorMsg>
                UserName Node not present
              </ErrorMsg>
              <ErrorCode>
                ERR_001
              </ErrorCode>
            </ERROR>
          </xsl:if>
          <xsl:if test="not(Password)">
            <ERROR>
              <ErrorMsg>
                Password Node not present
              </ErrorMsg>
              <ErrorCode>
                ERR_002
              </ErrorCode>
            </ERROR>
          </xsl:if>
          <xsl:if test="UserName=''">
            <ERROR>
              <ErrorMsg>
                UserName Node Contains Invalid Data
              </ErrorMsg>
              <ErrorCode>
                ERR_003
              </ErrorCode>
            </ERROR>
          </xsl:if>
          <xsl:if test="Password=''">
            <ERROR>
              <ErrorMsg>
                Password Node Contains Invalid Data
              </ErrorMsg>
              <ErrorCode>
                ERR_004
              </ErrorCode>
            </ERROR>
          </xsl:if>
          <xsl:value-of select="func:checkUserExist('UserName','Password')" />
        </OUTPUT>
      </xsl:for-each>
    </root>
</xsl:template>
</xsl:stylesheet>

For the above XSL, the below are code comments

Code Comment #1

xmlns:func="urn:actl-xslt"

Note the attribute that I have added here as - xmlns:func="urn:actl-xslt"

Code Comment #2

The prefix added to my external method func:checkUserExist('UserName','Password') as below

<xsl:value-of select="func:checkUserExist('UserName','Password')" />

Code Comment #3

<xsl:if test="not(UserName)">

This tag is used to check if USERNAME node exists or not

Code Comment #4

<xsl:if test="UserName=''">

This tag is used to check if content in USERNAME node is empty or not

Step 3: Define a function which will be called from XSL

This function will be called from XSL defined as <xsl:value-of select="func:checkUserExist('UserName','Password')" />

Instead of checking username against DB we are checking with a static value. If username matches it returns a Success string else it would return ErrorStrings

public string checkUserExist(string uName, string pWord)
    {
        string returnValue = string.Empty;
        if (uName == "prakash")
        {
            returnValue = " <SUCCESS> <SuccessMsg> SUCESSS </SuccessMsg><SuccessCode>SUC_000</SuccessCode> </SUCCESS> ";
        }
        else
        {
            returnValue = " <ERROR> <ErrorMsg>UserName/Password is invalid!.</ErrorMsg><ErrorCode>ERR_005</ErrorCode> </ERROR> ";
        }

        return returnValue;
    }

Step 4: Implement code to validate XML with XSL as follows which will be called from XSL.

This below function will be called in the main method & this function declares 3 main variables for XML input, XSL input & XML output as result.xml

    public void CheckUserXslt()
    {

        string sourceDoc = @"D:\Surya Prakash\WorkAround\GopalSample\XML\CheckUser.XML";
        string xsltDoc = @"D:\Surya Prakash\WorkAround\GopalSample\XML\CheckUser.xslt";
        string resultDoc = @"D:\Surya Prakash\WorkAround\GopalSample\XML\result.xml";
        XsltArgumentList xsltArguments = null;
        XsltExtension xsltExtension = new XsltExtension();
        xsltArguments = new XsltArgumentList();
        xsltArguments.AddExtensionObject("urn:actl-xslt", xsltExtension);

        XPathDocument myXPathDocument = new XPathDocument(sourceDoc);
        XslTransform myXslTransform = new XslTransform();
        XmlTextWriter writer = new XmlTextWriter(resultDoc, null);
        myXslTransform.Load(xsltDoc);
        myXslTransform.Transform(myXPathDocument, xsltArguments, writer);
        writer.Close();
        StreamReader stream = new StreamReader(resultDoc);