Custom Error Handler while Validating XML against XSD Schema

In this example we create a Custom Error Handler while Validating XML against XSD. We use the javax.xml.validation.Validator to check the XML document against the XSD schema. We can create a custom error handler which will handle the error generated from the validator.validate() method. Next we need to register our custom error handler using the validator.setErrorHandler() method. This will instruct the validator to use our custom error handler when there is an exception.

Project structure

+--src
|   +--main
|       +--java
|           +--com
|               +--memorynotfound
|                   |--ValidateXmlXsd.java
|       +--resources
|           |--schema.xsd
pom.xml

XSD Schema

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

    <xs:element name="course">
        <xs:complexType>
            <xs:all>
                <xs:element type="xs:string" name="name"/>
                <xs:element type="xs:string" name="description"/>
            </xs:all>
            <xs:attribute type="xs:integer" name="id"/>
        </xs:complexType>
    </xs:element>

</xs:schema>

Custom Error Handler while Validating XML against XSD

We can handle warnings, errrors or fatalErrors. When one of these events occure we can construct a custom error message. In this example the error message contains the line and column number and a message.

package com.memorynotfound.xml.xsd;

import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
/**
  * custom error handler while validating xml against xsd
  */
public class XsdErrorHandler implements ErrorHandler {

    @Override
    public void warning(SAXParseException exception) throws SAXException {
        handleMessage("Warning", exception);
    }

    @Override
    public void error(SAXParseException exception) throws SAXException {
        handleMessage("Error", exception);
    }

    @Override
    public void fatalError(SAXParseException exception) throws SAXException {
        handleMessage("Fatal", exception);
    }

    private String handleMessage(String level, SAXParseException exception) throws SAXException {
        int lineNumber = exception.getLineNumber();
        int columnNumber = exception.getColumnNumber();
        String message = exception.getMessage();
        throw new SAXException("[" + level + "] line nr: " + lineNumber + " column nr: " + columnNumber + " message: " + message);
    }
}

XSD Validator

To validate XML against XSD schema we need to create a schema. And create a validator. We also need to register our custom error handler. We do this by calling the validator.setErrorHandler() method with our custom error handler. When there is a validation exception the validator throws a SAXException. This exception will print our custom error handler exception.

package com.memorynotfound.xml.xsd;

import org.xml.sax.SAXException;

import javax.xml.XMLConstants;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;
import java.io.IOException;
import java.io.StringReader;

/**
  * custom error handler while validating xml against xsd
  */
public class ValidateXmlXsd {

    public static String xml =
            "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>\n" +
            "<course id=\"1-ID\">\n" +
            "    <name>JAX-B</name>\n" +
            "    <description>Validate XML against XSD Schema</description>\n" +
            "</course>";

    public static void main(String... args) {
        try {
            System.out.println("Custom Error Handler while Validating XML against XSD");
            SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
            Schema schema = factory.newSchema(ValidateXmlXsd.class.getResource("/schema.xsd"));
            Validator validator = schema.newValidator();
            validator.setErrorHandler(new XsdErrorHandler());
            validator.validate(new StreamSource(new StringReader(xml)));
            System.out.println("Validation is successful");
        } catch (IOException e) {
            // handle exception while reading source
        } catch (SAXException e) {
            System.out.println("Custom Error Handler while Validating XML against XSD");
            System.out.println("Message: " + e.getMessage());
        }
    }
}

Output

Validate XML against XSD Schema
Error when validate XML against XSD Schema
Message: [Error] line nr: 2 column nr: 19 message: cvc-datatype-valid.1.2.1: '1-ID' is not a valid value for 'integer'.

References

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