XML Validation with XSD Along With Custom Exception

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

This article describes the below items:

XML data validation with XSD like XML TAGS provided are present & appropriate with respect to XSD
How to write custom validations like check to see email ID is valid or not
How to generate XSD from XML
How to generate Custom Error, when XML data validation fails
How to write regular expression in XSD

Let get into a sample with below steps

Step 1: Define XML
Step 2: Generate/Define XSD
Step 3: Write code to validate XML with XSD
Step 4: Handle Exception in by defining Custom Exception

Step 1: First define XML as follows & name the XML file as Complex.XML

<Name>Surya Prakash</Name>

<Address>Malkajgiri</Address>

<Email>[email protected]</Email>
</Person>

Step 2: How to generate XSD? Simple follow below steps

Open Complex.XML file à Go to VS Menu à XML à Create Schema, this will generate XSD as below

<?xml version="1.0" encoding="utf-8"?>

<xs:schema xmlns:ns0="http://Testing.Message" attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="Person">

<xs:complexType>

<xs:sequence>

<xs:element name="Name" type="xs:string" />

<xs:element name="Address" type="xs:string" />

<xs:element name="Phone" type="xs:unsignedLong" />

<xs:element name="Email" type="xs:string" />

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:schema>

As we need to write code to check if Email ID is valid or not we can do this by regular expression, by changing EMAIL tag type from String to Custom Type as follows

<xs:element name="Email" type="ValidateEmail" />

As we have defined custom type we need to define its structure as follows

<xs:simpleType name="ValidateEmail">

<xs:restriction base="xs:string">

<xs:pattern value="[A-Za-z0-9_]+([-+.'][A-Za-z0-9_]+)*@[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*\.[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*" />

</xs:restriction>

</xs:simpleType>

Finally our XSD file will be as

<?xml version="1.0" encoding="utf-8"?>

<xs:schema xmlns:ns0="http://Testing.Message" attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="Person">

<xs:complexType>

<xs:sequence>

<xs:element name="Name" type="xs:string" />

<xs:element name="Address" type="xs:string" />

<xs:element name="Phone" type="xs:string" />

<xs:element name="Email" type="ValidateEmail" />

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:simpleType name="ValidateEmail">

<xs:restriction base="xs:string">

<xs:pattern value="[A-Za-z0-9_]+([-+.'][A-Za-z0-9_]+)*@[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*\.[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*" />

</xs:restriction>

</xs:simpleType>

</xs:schema>

Step 3: Create a new page as "Complex.aspx" & add a label to the form and name it as "lblMsg"

Go to Complex.aspx.cs & define class level global variable a

private int nErrors = 0;

private string strErrorMsg = string.Empty;

public string Errors { get { return strErrorMsg; } }

Go to Pageload event of Comple.aspx page

// IsValidXML return TRUE if no exception, false if any exceptions & respective message is appended to lblMsg

// IsValidXML takes 2 parameters, param1: XML path, param2: XSD path

if (!IsValidXml(@"D:\Surya Prakash\WorkAround\GopalSample\XML\Complex.xml", @"D:\Surya Prakash\WorkAround\GopalSample\XML\Complex.xsd"))
            lblMsg.Text = Errors;
        else
            lblMsg.Text = string.Format("Success");

IsValidXML function definition

public bool IsValidXml(string xmlPath, string xsdPath)
{
  bool bStatus = false;
  try
{
             // Declare local objects
             XmlReaderSettings rs = new XmlReaderSettings();
             rs.ValidationType = ValidationType.Schema;
             rs.ValidationFlags |= XmlSchemaValidationFlags.ProcessSchemaLocation | XmlSchemaValidationFlags.ReportValidationWarnings;
      // Event Handler for handling exception & this will be called whenever any mismatch between XML & XSD
          rs.ValidationEventHandler += new ValidationEventHandler(ValidationEventHandler);
           rs.Schemas.Add(null, XmlReader.Create(xsdPath));
// reading xml
  using (XmlReader xmlValidatingReader = XmlReader.Create(xmlPath, rs))
{ while (xmlValidatingReader.Read()) { } }
////Exception if error.
if (nErrors > 0) { throw new Exception(strErrorMsg);
}
else { bStatus = true; }//Success
}
        catch (Exception error) { bStatus = false; }
        return bStatus;
}

EventHandler body definition for handling any exception

void ValidationEventHandler(object sender, ValidationEventArgs e)
{
        if (e.Severity == XmlSeverityType.Warning) strErrorMsg += "WARNING: ";
        else strErrorMsg += "ERROR: ";
        nErrors++;
        if (e.Exception.Message.Contains("'Email' element is invalid"))
        {
            strErrorMsg = strErrorMsg + getErrorString("Provided Email data is Invalid", "CAPIEMAIL007") + "\r\n";
        }
        if (e.Exception.Message.Contains("The element 'Person' has invalid child element"))
        {
            strErrorMsg = strErrorMsg + getErrorString("Provided XML contains invalid child element", "CAPINVALID005") + "\r\n";
        }
        else
        {
            strErrorMsg = strErrorMsg + e.Exception.Message + "\r\n";
        }
    }

Step 4: getErrorString: Custom error generation in XML string format

string getErrorString(string erroString, string errorCode)
    {
        StringBuilder errXMl = new StringBuilder();
        errXMl.Append("<MyError> <errorString> ERROR_STRING </errorString> <errorCode> ERROR_CODE </errorCode> </MyError>");
        errXMl.Replace("ERROR_STRING", erroString);
        errXMl.Replace("ERROR_CODE", errorCode);
        return errXMl.ToString();