xalanxpathprocessor.java

用Java写的面相对象的数据库管理系统

// Copyright 1997-1999 by softwarebuero m&b (SMB). All rights reserved.
//
// You can redistribute this software and/or modify it under the terms of
// the Ozone Library License version 1 published by softwarebuero m&b (SMB).
//
// $Id: XalanXPathProcessor.java,v 1.7 2000/11/03 11:21:49 daniela Exp $

package org.ozoneDB.xml.xpath;

import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.traversal.NodeFilter;

import org.xml.sax.SAXException;

import org.apache.xalan.xpath.XPath;
import org.apache.xalan.xpath.XPathProcessorImpl;
import org.apache.xalan.xpath.XPathSupport;
import org.apache.xalan.xpath.xml.PrefixResolverDefault;


/**
 * This class implements the XPathProcessor interface on top of Xalan.<p>
 * 
 * This class only compiles if you have a working Xalan 1.0.1 in your classpath!
 * 
 * 
 * @version $Revision: 1.7 $ $Date: 2000/11/03 11:21:49 $
 * @author <a href="http://www.softwarebuero.de">SMB</a>
 */
public class XalanXPathProcessor extends java.lang.Object implements XPathProcessor {
    
    // Constants
    
    final static long serialVersionUID = 1;
    
    // Data
    
    protected XPathSupport xpathSupport;
    
    protected XPathProcessorImpl parser;
    
    protected XPath xpath;
    
    
    /**
     * The constructur initializes some basic but internal variables needed by
     * Xalans XPath implementation.
     */
    public XalanXPathProcessor() {
        // Since we don't have a XML Parser involved here, install some
        // default support for things like namespaces, etc.
        // xpathSupport = new XMLParserLiaisonDefault();
        xpathSupport = new NodeFilterLiaison();
        
        // sets the DocumentTraversal for this query
        ((NodeFilterLiaison)xpathSupport).setDocumentTraversal( new org.apache.xerces.dom.DocumentImpl() );
        
        // Create the XPath object.
        xpath = new XPath();
        
        // Create a XPath parser.
        parser = new XPathProcessorImpl( xpathSupport );
    }
    
    
    public XObject execute( XPathQuery _query, Node _rootNode ) throws SAXException {
        Node namespace = _query.namespace != null ? _query.namespace : _rootNode;
        return execute( _query.qstring, _rootNode, namespace, _query.filter );
    } 
    
    
    /**
     * Executes the specified query on the specified node using the specified
     * namespace resolver.
     * @param qString The XPath query string.
     * @param rootNode The node from which the query should start.
     * @param nameSpace The node that resolves namespace queries.
     * @param filter The node filter which is to apply while querying.
     * @exception SAXException If any error occurs.
     * @return The XObject insulating the query result.
     */
    protected XObject execute( String qString, Node rootNode, Node nameSpace, NodeFilter filter ) 
            throws org.xml.sax.SAXException {
        
        PrefixResolverDefault prefixResolver;
        
        if (rootNode.getNodeType() == Node.DOCUMENT_NODE) {
            rootNode = ((Document)rootNode).getDocumentElement();
        } 
        
        // Create an object to resolve namespace prefixes.
        // XPath namespaces are resolved from the input root node's
        // document element if it is a root node, or else the current root node.
        prefixResolver = nameSpace != null 
                ? new PrefixResolverDefault( nameSpace ) 
                : new PrefixResolverDefault( rootNode );
        
        // sets the filter for this query
        ((NodeFilterLiaison)xpathSupport).setNodeFilter( filter == null ? new SimpleNodeFilter() : filter );
        
        // parse the specified Query-String and build an Parse-Tree
        parser.initXPath( xpath, qString, prefixResolver );
        
        // execute the XPath query on the specified root node
        return new XalanXObject( xpath.execute( xpathSupport, rootNode, prefixResolver ) );
    } 
    
    
    public void writeExternal( ObjectOutput out ) throws IOException {
    // nothing to do
    } 
    
    
    public void readExternal( ObjectInput in ) throws IOException, ClassNotFoundException {
        xpathSupport = new NodeFilterLiaison();
        ((NodeFilterLiaison)xpathSupport).setDocumentTraversal( new org.apache.xerces.dom.DocumentImpl() );
        xpath = new XPath();
        parser = new XPathProcessorImpl( xpathSupport );
    } 
    
}