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Cayenne Object Persistence Framework
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/* ====================================================================
 * 
 * The ObjectStyle Group Software License, version 1.1
 * ObjectStyle Group - http://objectstyle.org/
 * 
 * Copyright (c) 2002-2005, Andrei (Andrus) Adamchik and individual authors
 * of the software. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * 3. The end-user documentation included with the redistribution, if any,
 *    must include the following acknowlegement:
 *    "This product includes software developed by independent contributors
 *    and hosted on ObjectStyle Group web site (http://objectstyle.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 * 
 * 4. The names "ObjectStyle Group" and "Cayenne" must not be used to endorse
 *    or promote products derived from this software without prior written
 *    permission. For written permission, email
 *    "andrus at objectstyle dot org".
 * 
 * 5. Products derived from this software may not be called "ObjectStyle"
 *    or "Cayenne", nor may "ObjectStyle" or "Cayenne" appear in their
 *    names without prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE OBJECTSTYLE GROUP OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 * 
 * This software consists of voluntary contributions made by many
 * individuals and hosted on ObjectStyle Group web site.  For more
 * information on the ObjectStyle Group, please see
 * .
 */
package org.objectstyle.cayenne.util;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

/**
 * The common superclass for all SAX event handlers used to parse the configuration file.
 * Each method just throws an exception, so subclasses should override what they can
 * handle. Each type of XML element (map, node, etc.) has a specific subclass. In the
 * constructor, this class takes over the handling of SAX events from the parent handler
 * and returns control back to the parent in the endElement method.
 * 
 * The idea to use nested handlers for XML document parsing (and code to implement it)
 * were taken from org.apache.tools.ant.ProjectHelper from Jakarta-Ant project (Copyright:
 * Apache Software Foundation). This may not be the best way to build objects from XML,
 * but it is rather consistent. For each nested element in the XML tree a dedicated
 * handler is created (subclass of this AbstractHandler). Once the element is parsed,
 * control is handled back to the parent handler.
 * 
 * 
 * @deprecated since 1.2 - this is moved to a non-public class in conf package.
 * @author Andrei Adamchik
 */
public class AbstractHandler extends DefaultHandler {

    /** Current parser. */
    protected XMLReader parser;

    /**
     * Previous handler for the document. When the next element is finished, control
     * returns to this handler.
     */
    protected ContentHandler parentHandler;

    /**
     * Creates a handler and sets the parser to use it for the current element.
     * 
     * @param parser Currently used XML parser. Must not be null.
     * @param parentHandler The handler which should be restored to the parser at the end
     *            of the element. Must not be null.
     */
    public AbstractHandler(XMLReader parser, ContentHandler parentHandler) {
        this.parentHandler = parentHandler;
        this.parser = parser;

        // Start handling SAX events
        parser.setContentHandler(this);
    }

    /** Returns currently used XMLReader. */
    public XMLReader getParser() {
        return parser;
    }

    /**
     * Handles the start of an element. This base implementation just throws an exception.
     * 
     * @exception SAXException if this method is not overridden, or in case of error in an
     *                overridden version
     */
    public void startElement(
            String namespaceURI,
            String localName,
            String qName,
            Attributes atts) throws SAXException {
        throw new SAXException(this.getClass().getName()
                + ": unexpected element \""
                + localName
                + "\"");
    }

    /**
     * Handles text within an element. This base implementation just throws an exception.
     * 
     * @param buf A character array of the text within the element. Will not be
     *            null.
     * @param start The start element in the array.
     * @param count The number of characters to read from the array.
     * @exception SAXException if this method is not overridden, or in case of error in an
     *                overridden version
     */
    public void characters(char[] buf, int start, int count) throws SAXException {
        String s = new String(buf, start, count).trim();

        if (s.length() > 0) {
            throw new SAXException(this.getClass().getName()
                    + ": unexpected text \""
                    + s
                    + "\"");
        }
    }

    /**
     * Called when this element and all elements nested into it have been handled.
     */
    protected void finished() {
    }

    /**
     * Handles the end of an element. Any required clean-up is performed by the finished()
     * method and then the original handler is restored to the parser.
     * 
     * @see #finished()
     */
    public void endElement(String namespaceURI, String localName, String qName)
            throws SAXException {
        finished();
        // Let parent resume handling SAX events
        parser.setContentHandler(parentHandler);
    }
}