// SAX default handler base class.
// No warranty; no copyright -- use this as you will.
// $Id: HandlerBase.java,v 1.5 1998/04/27 01:47:23 david Exp $

package org.xml.sax;

/**
  * Default base class for handlers.
  *
  * <p>This class implements the default behaviour for four SAX
  * interfaces: EntityResolver, DTDHandler, DocumentHandler,
  * and ErrorHandler.</p>
  *
  * <p>Application writers can extend this class when they need to
  * implement only part of an interface; parser writers can
  * instantiate this class to provide default handlers when the
  * application has not supplied its own.</p>
  *
  * <p>Note that the use of this class is optional.</p>
  *
  * @author David Megginson (ak117@freenet.carleton.ca)
  * @version 1.0
  * @see org.xml.sax.EntityResolver
  * @see org.xml.sax.DTDHandler
  * @see org.xml.sax.DocumentHandler
  * @see org.xml.sax.ErrorHandler
  */
public class HandlerBase
  implements EntityResolver, DTDHandler,
	     DocumentHandler, ErrorHandler
{


  //////////////////////////////////////////////////////////////////////
  // Default implementation of the EntityResolver interface.
  //////////////////////////////////////////////////////////////////////

  /**
    * Resolve an external entity.
    *
    * <p>Always return null, so that the parser will use the system
    * identifier provided in the XML document.  This method implements
    * the SAX default behaviour: application writers can override it
    * in a subclass to do special translations such as catalog lookups
    * or URI redirection.</p>
    *
    * @param publicId The public identifer, or null if none is
    *                 available.
    * @param systemId The system identifier provided in the XML 
    *                 document.
    * @return The new input source, or null to require the
    *         default behaviour.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.EntityResolver#resolveEntity
    */
  public InputSource resolveEntity (String publicId, String systemId)
    throws SAXException
  {
    return null;
  }



  //////////////////////////////////////////////////////////////////////
  // Default implementation of DTDHandler interface.
  //////////////////////////////////////////////////////////////////////


  /**
    * Receive notification of a notation declaration.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass if they wish to keep track of the notations
    * declared in a document.</p>
    *
    * @param name The notation name.
    * @param publicId The notation public identifier, or null if not
    *                 available.
    * @param systemId The notation system identifier.
    * @see org.xml.sax.DTDHandler#notationDecl
    */
  public void notationDecl (String name, String publicId, String systemId)
  {
    // no op
  }


  /**
    * Receive notification of an unparsed entity declaration.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to keep track of the unparsed entities
    * declared in a document.</p>
    *
    * @param name The entity name.
    * @param publicId The entity public identifier, or null if not
    *                 available.
    * @param systemId The entity system identifier.
    * @param notationName The name of the associated notation.
    * @see org.xml.sax.DTDHandler#unparsedEntityDecl
    */
  public void unparsedEntityDecl (String name, String publicId,
				  String systemId, String notationName)
  {
    // no op
  }



  //////////////////////////////////////////////////////////////////////
  // Default implementation of DocumentHandler interface.
  //////////////////////////////////////////////////////////////////////


  /**
    * Receive a Locator object for document events.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass if they wish to store the locator for use
    * with other document events.</p>
    *
    * @param locator A locator for all SAX document events.
    * @see org.xml.sax.DocumentHandler#setDocumentLocator
    * @see org.xml.sax.Locator
    */
  public void setDocumentLocator (Locator locator)
  {
    // no op
  }


  /**
    * Receive notification of the beginning of the document.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to take specific actions at the beginning
    * of a document (such as allocating the root node of a tree or
    * creating an output file).</p>
    *
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#startDocument
    */
  public void startDocument ()
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of the end of the document.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to take specific actions at the beginning
    * of a document (such as finalising a tree or closing an output
    * file).</p>
    *
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#endDocument
    */
  public void endDocument ()
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of the start of an element.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to take specific actions at the start of
    * each element (such as allocating a new tree node or writing
    * output to a file).</p>
    *
    * @param name The element type name.
    * @param attributes The specified or defaulted attributes.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#startElement
    */
  public void startElement (String name, AttributeList attributes)
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of the end of an element.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to take specific actions at the end of
    * each element (such as finalising a tree node or writing
    * output to a file).</p>
    *
    * @param name The element type name.
    * @param attributes The specified or defaulted attributes.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#endElement
    */
  public void endElement (String name)
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of character data inside an element.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method to take specific actions for each chunk of character data
    * (such as adding the data to a node or buffer, or printing it to
    * a file).</p>
    *
    * @param ch The characters.
    * @param start The start position in the character array.
    * @param length The number of characters to use from the
    *               character array.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#characters
    */
  public void characters (char ch[], int start, int length)
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of ignorable whitespace in element content.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method to take specific actions for each chunk of ignorable
    * whitespace (such as adding data to a node or buffer, or printing
    * it to a file).</p>
    *
    * @param ch The whitespace characters.
    * @param start The start position in the character array.
    * @param length The number of characters to use from the
    *               character array.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#ignorableWhitespace
    */
  public void ignorableWhitespace (char ch[], int start, int length)
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of a processing instruction.
    *
    * <p>By default, do nothing.  Application writers may override this
    * method in a subclass to take specific actions for each
    * processing instruction, such as setting status variables or
    * invoking other methods.</p>
    *
    * @param target The processing instruction target.
    * @param data The processing instruction data, or null if
    *             none is supplied.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.DocumentHandler#processingInstruction
    */
  public void processingInstruction (String target, String data)
    throws SAXException
  {
    // no op
  }



  //////////////////////////////////////////////////////////////////////
  // Default implementation of the ErrorHandler interface.
  //////////////////////////////////////////////////////////////////////


  /**
    * Receive notification of a parser warning.
    *
    * <p>The default implementation does nothing.  Application writers
    * may override this method in a subclass to take specific actions
    * for each warning, such as inserting the message in a log file or
    * printing it to the console.</p>
    *
    * @param e The warning information encoded as an exception.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.ErrorHandler#warning
    * @see org.xml.sax.SAXParseException
    */
  public void warning (SAXParseException e)
    throws SAXException
  {
    // no op
  }


  /**
    * Receive notification of a recoverable parser error.
    *
    * <p>The default implementation does nothing.  Application writers
    * may override this method in a subclass to take specific actions
    * for each error, such as inserting the message in a log file or
    * printing it to the console.</p>
    *
    * @param e The warning information encoded as an exception.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.ErrorHandler#warning
    * @see org.xml.sax.SAXParseException
    */
  public void error (SAXParseException e)
    throws SAXException
  {
    // no op
  }


  /**
    * Report a fatal XML parsing error.
    *
    * <p>The default implementation throws a SAXParseException.
    * Application writers may override this method in a subclass if
    * they need to take specific actions for each fatal error (such as
    * collecting all of the errors into a single report): in any case,
    * the application must stop all regular processing when this
    * method is invoked, since the document is no longer reliable, and
    * the parser may no longer report parsing events.</p>
    *
    * @param e The error information encoded as an exception.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see org.xml.sax.ErrorHandler#fatalError
    * @see org.xml.sax.SAXParseException
    */
  public void fatalError (SAXParseException e)
    throws SAXException
  {
    throw e;
  }

}
