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:
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:
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:
We define the Java class SAXValidator for SAX validation.
public class SAXValidator {
In the Java class we define a method validateXMLDocument.
public void validateXMLDocument(InputSource input) {
try {
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);
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());
}
}
We add the Java method getXMLSchema to create an XMLSchema object.
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.