xpath.java

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/*
 * Copyright 2000-2002,2004,2005 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.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.
 * 
 * @xerces.internal
 *
 * @author Andy Clark, IBM
 * @author Sunitha Reddy, Sun Microsystems
 * @version $Id: XPath.java,v 1.3 2005/09/26 13:02:31 sunithareddy 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_AXISNAME_ATTRIBUTE ||
                    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 ||
                    token == XPath.Tokens.EXPRTOKEN_AXISNAME_CHILD ||
                    token == XPath.Tokens.EXPRTOKEN_DOUBLE_COLON
                    ) {
                    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;
        boolean expectingDoubleColon = false;

        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;
                }
                case XPath.Tokens.EXPRTOKEN_AXISNAME_ATTRIBUTE: {
                     check(expectingStep);
                     expectingDoubleColon = true;
                    
                     if (xtokens.nextToken() == XPath.Tokens.EXPRTOKEN_DOUBLE_COLON){
                         Step step = new Step(
                         new Axis(Axis.ATTRIBUTE),
                                 parseNodeTest(xtokens.nextToken(),xtokens,context));
                         stepsVector.addElement(step);
                         expectingStep=false;
                         expectingDoubleColon = false;
                     }
                     break;
                }
                case XPath.Tokens.EXPRTOKEN_AXISNAME_CHILD:{
                    check(expectingStep);
                    expectingDoubleColon = true;
                    break;
                }
                case XPath.Tokens.EXPRTOKEN_DOUBLE_COLON :{
                    check(expectingStep);
                    check(expectingDoubleColon);
                    expectingDoubleColon = false;
                    break;
                }
                default:
                    // we should have covered all the tokens that we can possibly see. 
                    throw new XPathException("c-general-xpath");
           }
        }
        
        check(!expectingStep);

        locationPathsVector.addElement(buildLocationPath(stepsVector));

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


        if (DEBUG_XPATH_PARSE) {
            System.out.println(">>> "+fLocationPaths);
        }

    } // parseExpression(SymbolTable,NamespaceContext)

    /**
     * Used by {@link #parseExpression} to parse a node test
     * from the token list.
     */