String vendorParserClass = "org.apache.xerces.parsers.SAXParser";

XMLReader reader = XMLReaderFactory.createXMLReader(vendorParserClass);

    ContentHandler jTreeContentHandler= new  JTreeContentHandler(treeModel,base);
    ErrorHandler jTreeErrorHandler= new  JTreeErrorHandler();

   //регистрируем
    reader.setContentHandler(jTreeContentHandler);
    reader.setErrorHandler(jTreeErrorHandler);
    reader.setEntityResolver( new  SimpleEntityResolver());
    reader.setFeature("http://xml.org/sax/features/validation",true);

    InputSource inputSource =  new  InputSource(xmlURI);
    reader.parse(inputSource);

 class  JTreeContentHandler  implements  ContentHandler,LexicalHandler {
     private  DefaultTreeModel treeModel;
     private  DefaultMutableTreeNode current;

     private  Locator locator;
     private  Map namespaceMapping;

     public  JTreeContentHandler(DefaultTreeModel treeModel,
                               DefaultMutableTreeNode current) {
       this .treeModel = treeModel;
       this .current = current;
       this .namespaceMapping= new  HashMap();
    }
// Все методы ContentHandler выкладывать нестану, они работают

     public   void  setDocumentLocator(Locator locator){
       this .locator=locator;
    }
     public   void  startDocument()  throws  SAXException{
    }
     public   void  endDocument ()   throws  SAXException{
    }

     public   void  processingInstruction(String target,String data)  throws  SAXException{
      DefaultMutableTreeNode pi= new  DefaultMutableTreeNode("PI (target = '"+target+"',data= '"+data+"')");
      current.add(pi);
    }
     public   void  startPrefixMapping(String prefix,String uri){
      namespaceMapping.put(uri,prefix);
    }

     public   void  characters( char [] ch, int  start, int  length){
      String s= new  String(ch,start,length);
      DefaultMutableTreeNode data= new  DefaultMutableTreeNode("Символьные данные: '"+s+"'");
      current.add(data);
    }

// Эти методы (LexicalHandler) парсером не вызываются 
     public   void  startDTD(String name,String publicID,String systemID)  throws  SAXException{
      JOptionPane.showMessageDialog( null ,"DTD");
      DefaultMutableTreeNode dtdReference= new  DefaultMutableTreeNode("DTD для '"+name+"'");
       if (publicID!= null ){
        DefaultMutableTreeNode publicIDNode= new  DefaultMutableTreeNode("Публичный идентификатор: '"+publicID+"'");
        dtdReference.add(publicIDNode);
      }
       if (systemID!= null ){
        DefaultMutableTreeNode systemIDNode= new  DefaultMutableTreeNode("Системный ID: '"+systemID+"'");
        dtdReference.add(systemIDNode);
      }
      current.add(dtdReference);
    }

     public   void  endDTD()  throws  SAXException{
    }

     public   void  startEntity(String name) throws  SAXException{
     DefaultMutableTreeNode entity=  new  DefaultMutableTreeNode("Сущность: '"+name+"'");
     current.add(entity);
     current=entity;
    }
     public   void  endEntity(String name)  throws  SAXException{
      current=(DefaultMutableTreeNode)current.getParent();
    }

     public   void  startCDATA()  throws  SAXException{
      DefaultMutableTreeNode cdata=  new  DefaultMutableTreeNode("Секция CDATA");
      current.add(cdata);
      current=cdata;
    }
     public   void  endCDATA()  throws  SAXException{
      current=(DefaultMutableTreeNode)current.getParent();
    }

     public   void  comment( char [] ch,  int  start, int  length)  throws  SAXException{
      String comment= new  String(ch,start,length);
      DefaultMutableTreeNode commentNode=  new  DefaultMutableTreeNode(comment);
      current.add(commentNode);
    }

  }