public class ValidateXML {
 static String SCHEMA_LANGUAGE = "http://java.sun.com/xml/jaxp/properties/schemaLanguage";

 static String XML_SCHEMA = "http://www.w3.org/2001/XMLSchema";

 static String SCHEMA_SOURCE = "http://java.sun.com/xml/jaxp/properties/schemaSource";

 static boolean validatechecksuccess;

 static void validate(String xmlfilename, String shemafilename) {
  validatechecksuccess = true;
  File input = new File(xmlfilename);
  File schema = new File(shemafilename);
  SAXParserFactory factory = SAXParserFactory.newInstance();
  factory.setNamespaceAware(true);
  factory.setValidating(true);
  try {
   SAXParser parser = factory.newSAXParser();
   parser.setProperty(SCHEMA_LANGUAGE, XML_SCHEMA);
   parser.setProperty(SCHEMA_SOURCE, schema);
   parser.parse(input, new SAXErrorPrinter());
  } catch (SAXNotRecognizedException e) {
   System.err.println("Unknown property specified:" + e.getMessage());
  } catch (SAXNotSupportedException e) {
   System.err.println("Unsupported property specified:"
     + e.getMessage());
  } catch (ParserConfigurationException e) {
   System.err.println("Your SAX parser is not JAXP 1.2 compliant."
     + e.getMessage());
  } catch (SAXException e) {
   System.err.println("Your SAX parser is not JAXP 1.2 compliant."
     + e.getMessage());
  } catch (IOException e) {
   System.err.println("Your SAX parser is not JAXP 1.2 compliant."
     + e.getMessage());
  } catch (Exception e) {
   System.err.println("Your SAX parser is not JAXP 1.2 compliant."
     + e.getMessage());
  }
 }
}
这个类的静态方法validate第一个参数是需要验证的xml文档(*.xml)，第二个是相对应的schema文档(*.xsd)。其中还注册了一个ErrorHandler，在贴一个处理程序。
import java.text.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;

public class SAXErrorPrinter extends DefaultHandler {
 private MessageFormat message = new MessageFormat("({0}: {1}, {2}): {3}");

 private void print(SAXParseException x) {
  String msg = this.message.format(new Object[] { x.getSystemId(),
    new Integer(x.getLineNumber()),
    new Integer(x.getColumnNumber()), x.getMessage() });
  System.err.println(msg);
  ValidateXML.validatechecksuccess = false;
 }

 public void warning(SAXParseException x) {
  this.print(x);
 }

 public void error(SAXParseException x) {
  this.print(x);
 }

 public void fatalError(SAXParseException x) throws SAXParseException {
  this.print(x);
  throw x;
 }
}

XML Schema:XML Schema is an XML based alternative to DTD.An XML schema describes the structure of an XML document.The XML Schema language is also referred to as XML Schema Definition (XSD).

CSS = HTML Style Sheets:HTML uses predefined tags and the meaning of the tags are well understood.

XSL = XML Style Sheets:XML does not use predefined tags (we can use any tag-names we like), and the meaning of these tags are not well understood.