deferredentityreferenceimpl.java

来自「JAVA 所有包」· Java 代码 · 共 153 行

/*
 * Copyright 1999-2002,2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.xerces.internal.dom;

/**
 * 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.
 * 
 * @xerces.internal
 * 
 * @version $Id: DeferredEntityReferenceImpl.java,v 1.2.6.1 2005/08/31 10:40:39 sunithareddy Exp $
 * @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);
        baseURI = ownerDocument.getNodeValue(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