pruningelementstack.java

Java的面向对象数据库系统的源代码

/*
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 * 
 * This software is open source. 
 * See the bottom of this file for the licence.
 * 
 * $Id: PruningElementStack.java,v 1.7 2003/04/07 22:14:02 jstrachan Exp $
 */

package org.dom4j.io;

import org.dom4j.Element;
import org.dom4j.ElementHandler;

/** <p><code>PruningElementStack</code> is a stack of {@link Element} 
  * instances which will prune the tree when a path expression is reached. 
  * This is useful for parsing very large documents where children of the
  * root element can be processed individually rather than keeping them all
  * in memory at the same time.</p>
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.7 $
  */
class PruningElementStack extends ElementStack {

    /** ElementHandler to call when pruning occurs */
    private ElementHandler elementHandler;
 
    /** the element name path which denotes the node to remove from its parent
      * when it is complete (i.e. when it is popped from the stack).
      * The first entry in the path will be a child of the root node
      */
    private String[] path;

    /** The level at which a path match can occur. 
      * We match when we have popped the selected node so the 
      * and the lastElementIndex points to its parent so this
      * value should be path.length - 2
      */
    private int matchingElementIndex;
    
    
    
    public PruningElementStack(String[] path, ElementHandler elementHandler) {
        this.path = path;
        this.elementHandler = elementHandler;
        checkPath();
    }
    
    public PruningElementStack(String[] path, ElementHandler elementHandler, int defaultCapacity) {
        super(defaultCapacity);
        this.path = path;
        this.elementHandler = elementHandler;
        checkPath();
    }
    
    public Element popElement() {
        Element answer = super.popElement();
        
        if ( lastElementIndex == matchingElementIndex && lastElementIndex >= 0 ) {
            // we are popping the correct level in the tree
            // lets check if the path fits
            //
            // NOTE: this is an inefficient way of doing it - we could 
            // maintain a history of which parts matched?
            if ( validElement( answer, lastElementIndex + 1 ) ) {
                Element parent = null;
                for ( int i = 0; i <= lastElementIndex; i++ ) {
                    parent = stack[i];
                    if ( ! validElement( parent, i ) ) {
                        parent = null;
                        break;
                    }
                }
                if ( parent != null ) {
                    pathMatches(parent, answer);
                }
            }
        }
        return answer;
    }
    
    protected void pathMatches(Element parent, Element selectedNode) {
        //System.out.println( "Matched: " + selectedNode + " about to call handler" );
        
        //elementHandler.handle( selectedNode );
        elementHandler.onEnd(this);
        
        //System.out.println( "Pruning: removing " + selectedNode + " from parent: " + parent );
        parent.remove( selectedNode );
    }
    
    protected boolean validElement(Element element, int index) {
        String requiredName = path[index];
        String name = element.getName();
        if (requiredName == name) { 
            return true;
        }
        if (requiredName != null && name != null ) {
            return requiredName.equals( name );
        }
        return false;
    }
    
    
    private void checkPath() {
        if ( path.length < 2 ) {
            throw new RuntimeException( "Invalid path of length: " + path.length + " it must be greater than 2" );
        }
        matchingElementIndex = path.length - 2;
    }
}




/*
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 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 name "DOM4J" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of MetaStuff, Ltd.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "DOM4J"
 *    nor may "DOM4J" appear in their names without prior written
 *    permission of MetaStuff, Ltd. DOM4J is a registered
 *    trademark of MetaStuff, Ltd.
 *
 * 5. Due credit should be given to the DOM4J Project
 *    (http://dom4j.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS
 * ``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
 * METASTUFF, LTD. 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.
 *
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * $Id: PruningElementStack.java,v 1.7 2003/04/07 22:14:02 jstrachan Exp $
 */