This code snippet creates a Validator that you can use to validate an XML document represented as a DOMSource.
//create a DocumentBuilderFactory object
DBF=DocumentBuilderFactory.newInstance();
//activating namespaces support
DBF.setNamespaceAware(true);
//create a DocumentBuilder object
DB=DBF.newDocumentBuilder();
//get the Document from XML document
D=DB.parse(new File(XMLdoc));
//create a SchemaFactory object
SchemaFactory SF=SchemaFactory.newInstance
(XMLConstants.W3C_XML_SCHEMA_NS_URI);
//create a Schema object
Schema S=SF.newSchema(new File("schema_name.xsd"));
//create a Validator object
Validator V=S.newValidator();
//call validate method
V.validate(new DOMSource(D));