htmlcollectionimpl.java

Java的面向对象数据库系统的源代码

/**
 * org/ozone-db/xml/dom/html/HTMLCollectionImpl.java
 *
 * The contents of this file are subject to the OpenXML Public
 * License Version 1.0; you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 * http://www.openxml.org/license.html
 *
 * THIS SOFTWARE IS DISTRIBUTED ON AN "AS IS" BASIS WITHOUT WARRANTY
 * OF ANY KIND, EITHER EXPRESSED OR IMPLIED. THE INITIAL DEVELOPER
 * AND ALL CONTRIBUTORS SHALL NOT BE LIABLE FOR ANY DAMAGES AS A
 * RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. SEE THE LICENSE FOR THE SPECIFIC LANGUAGE GOVERNING
 * RIGHTS AND LIMITATIONS UNDER THE LICENSE.
 *
 * The Initial Developer of this code under the License is Assaf Arkin.
 * Portions created by Assaf Arkin are Copyright (C) 1998, 1999.
 * All Rights Reserved.
 */

package org.ozoneDB.xml.dom.html;

import org.ozoneDB.xml.dom.CollectionImpl;
import org.w3c.dom.Element;
import org.w3c.dom.html.*;


/**
 * Implements {@link org.w3c.dom.html.HTMLCollection} to traverse any named
 * elements on a {@link org.w3c.dom.html.HTMLDocument}. The elements type to
 * look for is identified in the constructor by code. This collection is not
 * optimized for traversing large trees.
 * <p>
 * The collection has to meet two requirements: it has to be live, and it has
 * to traverse depth first and always return results in that order. As such,
 * using an object container (such as {@link java.util.Vector}) is expensive on
 * insert/remove operations. Instead, the collection has been implemented using
 * three traversing functions. As a result, operations on large documents will
 * result in traversal of the entire document tree and consume a considerable
 * amount of time.
 * <p>
 * Note that synchronization on the traversed document cannot be achieved.
 * The document itself cannot be locked, and locking each traversed node is
 * likely to lead to a dead lock condition. Therefore, there is a chance of the
 * document being changed as results are fetched; in all likelihood, the results
 * might be out dated, but not erroneous.
 *
 *
 * @version $Revision: 1.2 $ $Date: 2003/11/20 23:18:42 $
 * @author <a href="mailto:[e-mail]">Assaf Arkin</a>
 * @see org.w3c.dom.html.HTMLCollection
 * @see org.ozoneDB.xml.dom.CollectionImpl
 */
final class HTMLCollectionImpl extends CollectionImpl implements HTMLCollection {


    /**
     * Returns true if scanning methods should iterate through the collection.
     * When looking for elements in the document, recursing is needed to traverse
     * the full document tree. When looking inside a specific element (e.g. for a
     * cell inside a row), recursing can lead to erroneous results.
     *
     * @return True if methods should recurse to traverse entire tree
     */
    protected boolean recurse() {
        return _lookingFor > 0;
    }


    /**
     * Determines if current element matches based on what we're looking for.
     * The element is passed along with an optional identifier name. If the
     * element is the one we're looking for, return true. If the name is also
     * specified, the name must match the <code>id</code> attribute
     * (match <code>name</code> first for anchors).
     *
     * @param elem The current element
     * @param name The identifier name or null
     * @return The element matches what we're looking for
     */
    protected boolean collectionMatch( Element elem, String name ) {
        boolean match;

        synchronized (elem) {
            // Begin with no matching. Depending on what we're looking for,
            // attempt to match based on the element type. This is the quickest
            // way to match involving only a cast. Do the expensive string
            // comparison later on.
            match = false;
            switch (_lookingFor) {
            case ANCHOR:
                // Anchor is an <A> element with a 'name' attribute. Otherwise, it's
                // just a link.
                match = elem instanceof HTMLAnchorElement && elem.getAttribute( "name" ) != null;
                break;
            case FORM:
                // Any <FORM> element.
                match = elem instanceof HTMLFormElement;
                break;
            case IMAGE:
                // Any <IMG> element. <OBJECT> elements with images are not returned.
                match = elem instanceof HTMLImageElement;
                break;
            case APPLET:
                // Any <APPLET> element, and any <OBJECT> element which represents an
                // Applet. This is determined by 'codetype' attribute being
                // 'application/java' or 'classid' attribute starting with 'java:'.
                match = elem instanceof HTMLAppletElement || elem instanceof HTMLObjectElement
                        && ("application/java".equals( elem.getAttribute( "codetype" ) ) || elem.getAttribute(
                        "classid" ) != null && elem.getAttribute( "classid" ).startsWith( "java:" ));
                break;
            case ELEMENT:
                // All form elements implement HTMLFormControl for easy identification.
                match = elem instanceof HTMLFormControl;
                break;
            case LINK:
                // Any <A> element, and any <AREA> elements with an 'href' attribute.
                match = (elem instanceof HTMLAnchorElement || elem instanceof HTMLAreaElement) && elem.getAttribute(
                        "href" ) != null;
                break;
            case AREA:
                // Any <AREA> element.
                match = elem instanceof HTMLAreaElement;
                break;
            case OPTION:
                // Any <OPTION> element.
                match = elem instanceof HTMLOptionElement;
                break;
            case ROW:
                // Any <TR> element.
                match = elem instanceof HTMLTableRowElement;
                break;
            case TBODY:
                // Any <TBODY> element (one of three table section types).
                match = elem instanceof HTMLTableSectionElement && elem.getTagName().equals( "tbody" );
                break;
            case CELL:
                // Any <TD> element.
                match = elem instanceof HTMLTableCellElement;
                break;
            }

            // If element type was matched and a name was specified, must also match
            // the name against either the 'id' or the 'name' attribute. The 'name'
            // attribute is relevant only for <A> elements for backward compatibility.
            if (match && name != null) {
                // If an anchor and 'name' attribute matches, return true. Otherwise,
                // try 'id' attribute.
                if (elem instanceof HTMLAnchorElement && name.equals( elem.getAttribute( "name" ) )) {
                    return true;
                }
                match = name.equals( elem.getAttribute( "id" ) );
            }
        }
        return match;
    }


    /**
     * Construct a new collection that retrieves element of the specific type
     * (<code>lookingFor</code>) from the specific document portion
     * (<code>topLevel</code>).
     *
     * @param topLevel The element underneath which the collection exists
     * @param lookingFor Code indicating what elements to look for
     */
    HTMLCollectionImpl( HTMLElement topLevel, short lookingFor ) {
        super( topLevel );
        _lookingFor = lookingFor;
    }


    /**
     * Request collection of all anchors in document: &lt;A&gt; elements that
     * have a <code>name</code> attribute.
     */
    final static short ANCHOR = 1;


    /**
     * Request collection of all forms in document: &lt;FORM&gt; elements.
     */
    final static short FORM = 2;


    /**
     * Request collection of all images in document: &lt;IMAGE&gt; elements.
     */
    final static short IMAGE = 3;


    /**
     * Request collection of all Applets in document: &lt;APPLET&gt; and
     * &lt;OBJECT&gt; elements (&lt;OBJECT&gt; must contain an Applet).
     */
    final static short APPLET = 4;


    /**
     * Request collection of all links in document: &lt;A&gt; and &lt;AREA&gt;
     * elements (must have a <code>href</code> attribute).
     */
    final static short LINK = 5;


    /**
     * Request collection of all options in selection: &lt;OPTION&gt; elments in
     * &lt;SELECT&gt; or &lt;OPTGROUP&gt;.
     */
    final static short OPTION = 6;


    /**
     * Request collection of all rows in table: &lt;TR&gt; elements in table or
     * table section.
     */
    final static short ROW = 7;


    /**
     * Request collection of all form elements: &lt;INPUT&gt;, &lt;BUTTON&gt;,
     * &lt;SELECT&gt;, &lt;TEXT&gt; and &lt;TEXTAREA&gt; elements inside form
     * &lt;FORM&gt;.
     */
    final static short ELEMENT = 8;


    /**
     * Request collection of all areas in map: &lt;AREA&gt; element in &lt;MAP&gt;
     * (non recursive).
     */
    final static short AREA = -1;


    /**
     * Request collection of all table bodies in table: &lt;TBODY&gt; element in
     * table &lt;TABLE&gt; (non recursive).
     */
    final static short TBODY = -2;


    /**
     * Request collection of all cells in row: &lt;TD&gt; elements in &lt;TR&gt;
     * (non recursive).
     */
    final static short CELL = -3;


    /**
     * Indicates what this collection is looking for. Holds one of the enumerated
     * values and used by {@link #collectionMatch}. Set by the constructor and
     * determine the collection's use for its life time.
     */
    private short _lookingFor;


}