src/org/apache/xerces/dom/DeferredEntityReferenceImpl.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  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 acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xerces" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
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 * 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 on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, International
 * Business Machines, Inc., http://www.apache.org.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.xerces.dom;

import org.w3c.dom.DocumentType;
import org.w3c.dom.Entity;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;

/**
 * EntityReference models the XML &entityname; syntax, when used for
 * entities defined by the DOM. Entities hardcoded into XML, such as
 * character entities, should instead have been translated into text
 * by the code which generated the DOM tree.
 * <P>
 * An XML processor has the alternative of fully expanding Entities
 * into the normal document tree. If it does so, no EntityReference nodes
 * will appear.
 * <P>
 * Similarly, non-validating XML processors are not required to read
 * or process entity declarations made in the external subset or
 * declared in external parameter entities. Hence, some applications
 * may not make the replacement value available for Parsed Entities 
 * of these types.
 * <P>
 * EntityReference behaves as a read-only node, and the children of 
 * the EntityReference (which reflect those of the Entity, and should
 * also be read-only) give its replacement value, if any. They are 
 * supposed to automagically stay in synch if the DocumentType is 
 * updated with new values for the Entity.
 * <P>
 * The defined behavior makes efficient storage difficult for the DOM
 * implementor. We can't just look aside to the Entity's definition
 * in the DocumentType since those nodes have the wrong parent (unless
 * we can come up with a clever "imaginary parent" mechanism). We
 * must at least appear to clone those children... which raises the
 * issue of keeping the reference synchronized with its parent.
 * This leads me back to the "cached image of centrally defined data"
 * solution, much as I dislike it.
 * <P>
 * For now I have decided, since REC-DOM-Level-1-19980818 doesn't
 * cover this in much detail, that synchronization doesn't have to be
 * considered while the user is deep in the tree. That is, if you're
 * looking within one of the EntityReferennce's children and the Entity
 * changes, you won't be informed; instead, you will continue to access
 * the same object -- which may or may not still be part of the tree.
 * This is the same behavior that obtains elsewhere in the DOM if the
 * subtree you're looking at is deleted from its parent, so it's
 * acceptable here. (If it really bothers folks, we could set things
 * up so deleted subtrees are walked and marked invalid, but that's
 * not part of the DOM's defined behavior.)
 * <P>
 * As a result, only the EntityReference itself has to be aware of
 * changes in the Entity. And it can take advantage of the same
 * structure-change-monitoring code I implemented to support
 * DeepNodeList.
 * 
 * @version $Id$
 * @since  PR-DOM-Level-1-19980818.
 */
public class DeferredEntityReferenceImpl 
    extends EntityReferenceImpl 
    implements DeferredNode {

    //
    // Constants
    //

    /** Serialization version. */
    static final long serialVersionUID = 390319091370032223L;
    
    //
    // Data
    //

    /** Node index. */
    protected transient int fNodeIndex;

    //
    // Constructors
    //

    /**
     * This is the deferred constructor. Only the fNodeIndex is given here. 
     * All other data, can be requested from the ownerDocument via the index.
     */
    DeferredEntityReferenceImpl(DeferredDocumentImpl ownerDocument,
                                int nodeIndex) {
        super(ownerDocument, null);

        fNodeIndex = nodeIndex;
        needsSyncData(true);

    } // <init>(DeferredDocumentImpl,int)

    //
    // DeferredNode methods
    //

    /** Returns the node index. */
    public int getNodeIndex() {
        return fNodeIndex;
    }

    //
    // Protected methods
    //

    /** 
     * Synchronize the entity data. This is special because of the way
     * that the "fast" version stores the information.
     */
    protected void synchronizeData() {

        // no need to sychronize again
        needsSyncData(false);

        // get the node data
        DeferredDocumentImpl ownerDocument =
            (DeferredDocumentImpl)this.ownerDocument;
        name = ownerDocument.getNodeName(fNodeIndex);
        
    } // synchronizeData()

    /** Synchronize the children. */
    protected void synchronizeChildren() {

        // no need to synchronize again
        needsSyncChildren(false);

        // get children
        isReadOnly(false);
        DeferredDocumentImpl ownerDocument =
            (DeferredDocumentImpl) ownerDocument();
        ownerDocument.synchronizeChildren(this, fNodeIndex);
        setReadOnly(true, true);

    } // synchronizeChildren()

} // class DeferredEntityReferenceImpl