Schema validation with a SAX parser

In this section we shall validate the example XML document catalog.xml with XML schema document catalog.xsd, with the SAXParser class. Import the oracle.xml.parser.schema and oracle.xml.parser.v2 packages.

Creating a SAX parser

Create a SAXParser object and set the validation mode of the SAXParser object to SCHEMA_VALIDATION, as shown in the following listing:

SAXParser saxParser=new SAXParser(); saxParser.setValidationMode(XMLParser.SCHEMA_VALIDATION);

The different validation modes that may be set on a SAXParser are discussed in the following table; but we only need the SCHEMA-based validation modes:

Next, create an XMLSchema object from the schema document with which an XML document is to be validated. An XMLSchema object represents the DOM structure of an XML schema document and is created with an XSDBuilder class object. Create an XSDBuilder object and invoke the build(InputSource) method of the XSDBuilder object to obtain an XMLSchema object. The InputSource object is created with an InputStream object created from the example XML schema document, catalog.xsd. As discussed before, we have used an InputSource object because most SAX implementations are InputSource based. The procedure to obtain an XMLSchema object is shown in the following listing:

XSDBuilder builder = new XSDBuilder();
InputStream inputStream=new FileInputStream(new File("catalog.xsd"));
InputSource inputSource=new InputSource(inputStream);
XMLSchema schema = builder.build(inputSource);

Set the XMLSchema object on the SAXParser object with setXMLSchema(XMLSchema) method:

saxParser.setXMLSchema(schema);

Setting the error handler

As in the previous section, define an error handling class, CustomErrorHandler that extends DefaultHandler class. Create an object of type CustomErrorHandler, and register the ErrorHandler object with the SAXParser as shown here:

CustomErrorHandler errorHandler = new CustomErrorHandler();
saxParser.setErrorHandler(errorHandler);

Validating the XML document

The SAXParser class extends the XMLParser class, which provides the overloaded parse methods discussed in the following table to parse an XML document:

Create an InputSource object from the XML document to be validated, and parse the XML document with the parse(InputSource) object:

InputStream inputStream=new FileInputStream(new
File("catalog.xml"));
InputSource inputSource=new InputSource(inputStream);
saxParser.parse(inputSource);

Running the Java application

The validation application SAXValidator.java is listed in the following listing with additional explanations:

  1. First we declare the import statements for the classes that we need. 
    import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import oracle.xml.parser.schema.*;
import oracle.xml.parser.v2.*;
import java.io.IOException;
import java.io.InputStream;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.InputSource;
  2. We define the Java class SAXValidator for SAX validation. 
    public class SAXValidator {
  3. In the Java class we define a method validateXMLDocument. 
    public void validateXMLDocument(InputSource input) {
try {
  4. In the method we create a SAXParser and set the XML schema on the SAXParser. 
    SAXParser saxParser = new SAXParser();
saxParser.setValidationMode(XMLParser.SCHEMA_VALIDATION);
XMLSchema schema=getXMLSchema();
saxParser.setXMLSchema(schema);
  5. To handle errors we create a custom error handler. We set the error handler on the SAXParser object and parse the XML document to be validated and also output validation errors if any. 
    CustomErrorHandler errorHandler = new CustomErrorHandler();
saxParser.setErrorHandler(errorHandler);
saxParser.parse(input);
if (errorHandler.hasValidationError == true) {
System.err.println("XML Document has
Validation Error:" + errorHandler.saxParseException.getMessage());
} else {
System.out.println("XML Document validates
with XML schema");
}
} catch (IOException e) {
System.err.println("IOException " + e.getMessage());
} catch (SAXException e) {
System.err.println("SAXException " + e.getMessage());
}
}
  6. We add the Java method getXMLSchema to create an XMLSchema object. 
    public XMLSchema getXMLSchema() {
try {
XSDBuilder builder = new XSDBuilder();
InputStream inputStream =
new FileInputStream(new File("catalog.xsd"));
InputSource inputSource = new
InputSource(inputStream);
XMLSchema schema = builder.build(inputSource);
return schema;
} catch (XSDException e) {
System.err.println("XSDException " + e.getMessage());
} catch (FileNotFoundException e) {
System.err.println("FileNotFoundException " +
e.getMessage());
}
return null;
}
  7. We define the main method in which we create an instance of the SAXValidator class and invoke the validateXMLDocument method. 
    public static void main(String[] argv) {
try {
InputStream inputStream =
new FileInputStream(new File("catalog.xml"));
InputSource inputSource=new InputSource(inputStream);
SAXValidator validator = new SAXValidator();
validator.validateXMLDocument(inputSource);
} catch (FileNotFoundException e) {
System.err.println("FileNotFoundException " +
e.getMessage());
}
}
  8. Finally, we define the custom error handler class as an inner class CustomErrorHandler to handle validation errors. 
    private class CustomErrorHandler extends DefaultHandler {
protected boolean hasValidationError = false;
protected SAXParseException saxParseException = null;
public void error(SAXParseException exception)
{
hasValidationError = true;
saxParseException = exception;
}
public void fatalError(SAXParseException exception)
{
hasValidationError = true;
saxParseException = exception;
}
public void warning(SAXParseException exception)
{
}
}
}

Copy the SAXValidator.java application to SAXValidator.java in the SchemaValidation project. To demonstrate error handling, add a title element to the journal element.

To run the SAXValidator.java application, right-click on SAXValidator.java in Application Navigator, and select Run. A validation error gets outputted. The validation error indicates that the title element is not expected.

Running the Java application
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