How to validate XML against XSD and parse/save in one step using SAXParser?

Question

How to validate XML against XSD and parse/save in one step using SAXParser?
I currently have an XML file and XSD. The XML file specifies the location of the XSD. In Java code I create a SAXParser with parameters indicating that it needs to validate the XML. However, SAXParser.parse does not validate the XML, but it does call my handler functions which save the elements/attributes in memory as it is read. On the other hand, XMLReader.parse does validate the XML against the XSD, but does not save the document in memory.
My code can call XMLReader.parse to validate the XML followed by SAXParser.parse to save the XML document in memory. But this sound inefficient. Besides, while a valid document is being parsed by XMLReader, it can be changed to be invalid and saved, and XMLReader.parse would be looking at the original file and would think that the file is OK, and then SAXParser.parse would parse the document without errors.
<Book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="book.xsd" name="MyBook">
  <Chapter name="First Chapter"/>
  <Chapter name="Second Chapter">
    <Section number="1"/>
    <Section number="2"/>
  </Chapter>
</Book>
<?xml version="1.0" encoding="ISO-8859-1" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="Book">
<xs:complexType>
  <xs:sequence>
   <xs:element name="Chapter" minOccurs="0" maxOccurs="unbounded">
    <xs:complexType>
     <xs:sequence>
      <xs:element name="Section" minOccurs="0" maxOccurs="unbounded">
       <xs:complexType>
        <xs:attribute name="xnumber"/>
      </xs:complexType>
      </xs:element>
     </xs:sequence>
     <xs:attribute name="name"/>
    </xs:complexType>
   </xs:element>
  </xs:sequence>
  <xs:attribute name="name"/>
</xs:complexType>
</xs:element>
</xs:schema>
public class SAXXMLParserTest
   public static void main(String[] args)
      try
         SAXParserFactory factory = SAXParserFactory.newInstance();
         factory.setNamespaceAware(true);
         factory.setValidating(true);
         SAXParser parser = factory.newSAXParser();
         parser.setProperty("http://java.sun.com/xml/jaxp/properties/schemaLanguage",
                            "http://www.w3.org/2001/XMLSchema");
         BookHandler handler = new BookHandler();
         XMLReader reader = parser.getXMLReader();
         reader.setErrorHandler(handler);
         parser.parse("xmltest.dat", handler); // does not throw validation error
         Book book = handler.getBook();
         System.out.println(book);
         reader.parse("xmltest.dat"); // throws validation error because of 'xnumber' in the XSD
public class Book extends Element
   private String name;
   private List<Chapter> chapters = new ArrayList<Chapter>();
   public Book(String name)
      this.name = name;
   public void addChapter(Chapter chapter)
      chapters.add(chapter);
   public String toString()
      StringBuilder builder = new StringBuilder();
      builder.append("<Book name=\"").append(name).append("\">\n");
      for (Chapter chapter: chapters)
         builder.append(chapter.toString());
      builder.append("</Book>\n");
      return builder.toString();
   public static class BookHandler extends DefaultHandler
      private Stack<Element> root = null;
      private Book book = null;
      public void startDocument()
         root = new Stack<Element>();
      public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException
         if (qName.equals("Book"))
            String name = attributes.getValue("name");
            root.push(new Book(name));
         else if (qName.equals("Chapter"))
            String name = attributes.getValue("name");
            Chapter child = new Chapter(name);
            ((Book)root.peek()).addChapter(child);
            root.push(child);
         else if (qName.equals("Section"))
            Integer number = Integer.parseInt(attributes.getValue("number"));
            Section child = new Section(number);
            ((Chapter)root.peek()).addSection(child);
            root.push(child);
      public void endElement(String uri, String localName, String qName) throws SAXException
         Element finished = root.pop();
         if (root.size() == 0)
            book = (Book) finished;
      public Book getBook()
         return book;
      public void error(SAXParseException e)
         System.out.println(e.getMessage());
      public void fatalError(SAXParseException e)
         error(e);
      public void warning(SAXParseException e)
         error(e);
public class Chapter extends Element
   public static class Section extends Element
      private Integer number;
      public Section(Integer number)
         this.number = number;
      public String toString()
         StringBuilder builder = new StringBuilder();
         builder.append("<Section number=\"").append(number).append("\"/>\n");
         return builder.toString();
   private String name;
   private List<Section> sections = null;
   public Chapter(String name)
      this.name = name;
   public void addSection(Section section)
      if (sections == null)
         sections = new ArrayList<Section>();
      sections.add(section);
   public String toString()
      StringBuilder builder = new StringBuilder();
      builder.append("<Chapter name=\"").append(name).append("\">\n");
      if (sections != null)
         for (Section section: sections)
            builder.append(section.toString());
      builder.append("</Chapter>\n");
      return builder.toString();
}Edited by: sn72 on Oct 28, 2008 1:16 PM

Answer 1

Have you looked at the XML DB FAQ thread (second post) in this forum? It has some examples for validating XML against schemas.