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The Validator.nu HTML Parser is an implementation of the HTML5 parsing algorithm in Java for applications. The parser is designed to work as a drop-in replacement for the XML parser in applications that already support XHTML 1.x content with an XML parser and use SAX, DOM or XOM to interface with the parser.
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/*
 * Copyright (c) 2007 Henri Sivonen
 * Copyright (c) 2008 Mozilla Foundation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a 
 * copy of this software and associated documentation files (the "Software"), 
 * to deal in the Software without restriction, including without limitation 
 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 
 * and/or sell copies of the Software, and to permit persons to whom the 
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in 
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
 * DEALINGS IN THE SOFTWARE.
 */

package nu.validator.saxtree;

import java.util.LinkedList;
import java.util.List;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.ext.LexicalHandler;

/**
 * Builds a SAX Tree representation of a document or a fragment 
 * streamed as ContentHandler and 
 * LexicalHandler events. The start/end event matching 
 * is expected to adhere to the SAX API contract. Things will 
 * simply break if this is not the case. Fragments are expected to
 * omit startDocument() and endDocument()
 * calls.
 * 
 * @version $Id$
 * @author hsivonen
 */
public class TreeBuilder implements ContentHandler, LexicalHandler {

    /**
     * The locator.
     */
    private Locator locator;

    /**
     * The current node.
     */
    private ParentNode current;

    /**
     * Whether to retain attribute objects.
     */
    private final boolean retainAttributes;

    /**
     * The prefix mappings for the next element to be inserted.
     */
    private List prefixMappings;
    
    /**
     * Constructs a reusable TreeBuilder that builds 
     * Documents and copies attributes.
     */
    public TreeBuilder() {
        this(false, false);
    }
    
    /**
     * The constructor. The instance will be reusabe if building a full 
     * document and not reusable if building a fragment.
     * 
     * @param fragment whether this TreeBuilder should build 
     * a DocumentFragment instead of a Document.
     * @param retainAttributes whether instances of the Attributes
     * interface passed to startElement should be retained 
     * (the alternative is copying).
     */
    public TreeBuilder(boolean fragment, boolean retainAttributes) {
        if (fragment) {
            current = new DocumentFragment();
        }
        this.retainAttributes = retainAttributes;
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#characters(char[], int, int)
     */
    public void characters(char[] ch, int start, int length) throws SAXException {
        current.appendChild(new Characters(locator, ch, start, length));
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#endDocument()
     */
    public void endDocument() throws SAXException {
        current.setEndLocator(locator);
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#endElement(java.lang.String, java.lang.String, java.lang.String)
     */
    public void endElement(String uri, String localName, String qName) throws SAXException {
        current.setEndLocator(locator);
        current = current.getParentNode();
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#endPrefixMapping(java.lang.String)
     */
    public void endPrefixMapping(String prefix) throws SAXException {
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#ignorableWhitespace(char[], int, int)
     */
    public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
        current.appendChild(new IgnorableWhitespace(locator, ch, start, length));
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#processingInstruction(java.lang.String, java.lang.String)
     */
    public void processingInstruction(String target, String data) throws SAXException {
        current.appendChild(new ProcessingInstruction(locator, target, data));
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#setDocumentLocator(org.xml.sax.Locator)
     */
    public void setDocumentLocator(Locator locator) {
        this.locator = locator;
    }

    public void skippedEntity(String name) throws SAXException {
        current.appendChild(new SkippedEntity(locator, name));
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#startDocument()
     */
    public void startDocument() throws SAXException {
        current = new Document(locator);
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#startElement(java.lang.String, java.lang.String, java.lang.String, org.xml.sax.Attributes)
     */
    public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
        current = (ParentNode) current.appendChild(new Element(locator, uri, localName, qName, atts, retainAttributes, prefixMappings));
        prefixMappings = null;
    }

    /**
     * 
     * @see org.xml.sax.ContentHandler#startPrefixMapping(java.lang.String, java.lang.String)
     */
    public void startPrefixMapping(String prefix, String uri) throws SAXException {
        if (prefixMappings == null) {
            prefixMappings = new LinkedList();
        }
        prefixMappings.add(new PrefixMapping(prefix, uri));
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#comment(char[], int, int)
     */
    public void comment(char[] ch, int start, int length) throws SAXException {
        current.appendChild(new Comment(locator, ch, start, length));
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#endCDATA()
     */
    public void endCDATA() throws SAXException {
        current.setEndLocator(locator);
        current = current.getParentNode();
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#endDTD()
     */
    public void endDTD() throws SAXException {
        current.setEndLocator(locator);
        current = current.getParentNode();
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#endEntity(java.lang.String)
     */
    public void endEntity(String name) throws SAXException {
        current.setEndLocator(locator);
        current = current.getParentNode();
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#startCDATA()
     */
    public void startCDATA() throws SAXException {
        current = (ParentNode) current.appendChild(new CDATA(locator));        
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#startDTD(java.lang.String, java.lang.String, java.lang.String)
     */
    public void startDTD(String name, String publicId, String systemId) throws SAXException {
        current = (ParentNode) current.appendChild(new DTD(locator, name, publicId, systemId));        
    }

    /**
     * 
     * @see org.xml.sax.ext.LexicalHandler#startEntity(java.lang.String)
     */
    public void startEntity(String name) throws SAXException {
        current = (ParentNode) current.appendChild(new Entity(locator, name));        
    }

    /**
     * Returns the root (Document if building a full document or 
     * DocumentFragment if building a fragment.).
     * 
     * @return the root
     */
    public ParentNode getRoot() {
        return current;
    }
}