xpath.java

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/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 2000-2002 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
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 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    distribution.
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 *       "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.
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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 com.sun.org.apache.xerces.internal.impl.xpath;

import java.util.Vector;

import com.sun.org.apache.xerces.internal.util.SymbolTable;
import com.sun.org.apache.xerces.internal.util.XMLSymbols;
import com.sun.org.apache.xerces.internal.util.XMLChar;
import com.sun.org.apache.xerces.internal.xni.NamespaceContext;
import com.sun.org.apache.xerces.internal.xni.QName;

/**
 * Bare minimum XPath parser.
 *
 * @author Andy Clark, IBM
 * @version $Id: XPath.java,v 1.13 2004/02/09 22:50:01 kohsuke Exp $
 */
public class XPath {

    //
    // Constants
    //

    private static final boolean DEBUG_ALL = false;

    private static final boolean DEBUG_XPATH_PARSE = DEBUG_ALL || false;

    private static final boolean DEBUG_ANY = DEBUG_XPATH_PARSE;

    //
    // Data
    //

    /** Expression. */
    protected String fExpression;

    /** Symbol table. */
    protected SymbolTable fSymbolTable;

    /** Location paths. */
    protected LocationPath[] fLocationPaths;

    //
    // Constructors
    //

    /** Constructs an XPath object from the specified expression. */
    public XPath(String xpath, SymbolTable symbolTable,
                 NamespaceContext context)
        throws XPathException {
        fExpression = xpath;
        fSymbolTable = symbolTable;
        parseExpression(context);
    } // <init>(String,SymbolTable,NamespaceContext)

    //
    // Public methods
    //

    /**
     * Returns a representation of all location paths for this XPath.
     * XPath = locationPath ( '|' locationPath)
     */
    public LocationPath[] getLocationPaths() {
        LocationPath[] ret=new LocationPath[fLocationPaths.length];
        for (int i=0;i<fLocationPaths.length;i++){
            ret[i]=(LocationPath)fLocationPaths[i].clone();
        }
        return ret;
    } // getLocationPath(LocationPath)

    /** Returns a representation of the first location path for this XPath. */
    public LocationPath getLocationPath() {
        return (LocationPath)fLocationPaths[0].clone();
    } // getLocationPath(LocationPath)

    //
    // Object methods
    //

    /** Returns a string representation of this object. */
    public String toString() {
        StringBuffer buf=new StringBuffer();
        for (int  i=0;i<fLocationPaths.length;i++){
            if (i>0){
                buf.append("|");
            }
            buf.append(fLocationPaths[i].toString());
        }
        return buf.toString();
    } // toString():String

    //
    // Private methods
    //

    /**
     * Used by the {@link #parseExpression(NamespaceContext)} method
     * to verify the assumption.
     * 
     * If <tt>b</tt> is false, this method throws XPathException
     * to report the error.
     */
    private static void check( boolean b ) throws XPathException {
        if(!b)      throw new XPathException("c-general-xpath");
    }
    
    /**
     * Used by the {@link #parseExpression(NamespaceContext)} method
     * to build a {@link LocationPath} object from the accumulated
     * {@link Step}s.
     */
    private LocationPath buildLocationPath( Vector stepsVector ) throws XPathException {
        int size = stepsVector.size();
        check(size!=0);
        Step[] steps = new Step[size];
        stepsVector.copyInto(steps);
        stepsVector.removeAllElements();
        
        return new LocationPath(steps);
    }
    
    /**
     * This method is implemented by using the XPathExprScanner and
     * examining the list of tokens that it returns.
     */
    private void parseExpression(final NamespaceContext context)
        throws XPathException {

        // tokens
        final XPath.Tokens xtokens = new XPath.Tokens(fSymbolTable);

        // scanner
        XPath.Scanner scanner = new XPath.Scanner(fSymbolTable) {
            protected void addToken(XPath.Tokens tokens, int token)
                throws XPathException {
                if (
                    token == XPath.Tokens.EXPRTOKEN_ATSIGN ||
                    token == XPath.Tokens.EXPRTOKEN_NAMETEST_QNAME ||
                    token == XPath.Tokens.EXPRTOKEN_OPERATOR_SLASH ||
                    token == XPath.Tokens.EXPRTOKEN_PERIOD ||
                    token == XPath.Tokens.EXPRTOKEN_NAMETEST_ANY ||
                    token == XPath.Tokens.EXPRTOKEN_NAMETEST_NAMESPACE ||
                    token == XPath.Tokens.EXPRTOKEN_OPERATOR_DOUBLE_SLASH ||
                    token == XPath.Tokens.EXPRTOKEN_OPERATOR_UNION
                    //
                    ) {
                    super.addToken(tokens, token);
                    return;
                }
                throw new XPathException("c-general-xpath");
            }
        };

        int length = fExpression.length();
        
        boolean success = scanner.scanExpr(fSymbolTable,
                                           xtokens, fExpression, 0, length);
        if(!success)
            throw new XPathException("c-general-xpath");
        
        //fTokens.dumpTokens();
        Vector stepsVector = new Vector();
        Vector locationPathsVector= new Vector();
        
        // true when the next token should be 'Step' (as defined in
        // the production rule [3] of XML Schema P1 section 3.11.6
        // if false, we are expecting either '|' or '/'.
        //
        // this is to make sure we can detect a token list like
        // 'abc' '/' '/' 'def' 'ghi'
        boolean expectingStep = true;

        while(xtokens.hasMore()) {
            final int token = xtokens.nextToken();

            switch (token) {
                case  XPath.Tokens.EXPRTOKEN_OPERATOR_UNION :{
                    check(!expectingStep);
                    locationPathsVector.addElement(buildLocationPath(stepsVector));
                    expectingStep=true;
                    break;
                }

                case XPath.Tokens.EXPRTOKEN_ATSIGN: {
                    check(expectingStep);
                    Step step = new Step(
                            new Axis(Axis.ATTRIBUTE),
                            parseNodeTest(xtokens.nextToken(),xtokens,context));
                    stepsVector.addElement(step);
                    expectingStep=false;
                    break;
                }
                case XPath.Tokens.EXPRTOKEN_NAMETEST_ANY:
                case XPath.Tokens.EXPRTOKEN_NAMETEST_NAMESPACE:
                case XPath.Tokens.EXPRTOKEN_NAMETEST_QNAME: {
                    check(expectingStep);
                    Step step = new Step(
                            new Axis(Axis.CHILD),
                            parseNodeTest(token,xtokens,context));
                    stepsVector.addElement(step);
                    expectingStep=false;
                    break;
                }

                case XPath.Tokens.EXPRTOKEN_PERIOD: {
                    check(expectingStep);
                    expectingStep=false;

                    // unless this is the first step in this location path,
                    // there's really no reason to keep them in LocationPath.
                    // This amounts to shorten "a/././b/./c" to "a/b/c".
                    // Also, the matcher fails to work correctly if XPath
                    // has those redundant dots. 
                    if (stepsVector.size()==0) {
                        // build step
                        Axis axis = new Axis(Axis.SELF);
                        NodeTest nodeTest = new NodeTest(NodeTest.NODE);
                        Step step = new Step(axis, nodeTest);
                        stepsVector.addElement(step);
                        
                        if( xtokens.hasMore()
                         && xtokens.peekToken() == XPath.Tokens.EXPRTOKEN_OPERATOR_DOUBLE_SLASH){
                            // consume '//'
                            xtokens.nextToken();    
                            
                            // build step
                            axis = new Axis(Axis.DESCENDANT);
                            nodeTest = new NodeTest(NodeTest.NODE);
                            step = new Step(axis, nodeTest);
                            stepsVector.addElement(step);
                            expectingStep=true;
                        }
                    }
                    break;
                }

                case XPath.Tokens.EXPRTOKEN_OPERATOR_DOUBLE_SLASH:{
                    // this cannot appear in arbitrary position.
                    // it is only allowed right after '.' when
                    // '.' is the first token of a location path.
                    throw new XPathException("c-general-xpath");
                }
                case XPath.Tokens.EXPRTOKEN_OPERATOR_SLASH: {
                    check(!expectingStep);
                    expectingStep=true;
                    break;
                }
                default:
                    // we should have covered all the tokens that we can possibly see. 
                    throw new InternalError();
            }
        }
        
        check(!expectingStep);

        locationPathsVector.addElement(buildLocationPath(stepsVector));

        // save location path
        fLocationPaths=new LocationPath[locationPathsVector.size()];
        locationPathsVector.copyInto(fLocationPaths);