001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.jxpath.ri;
018
019import java.io.StringReader;
020
021import org.apache.commons.jxpath.JXPathInvalidSyntaxException;
022import org.apache.commons.jxpath.ri.parser.ParseException;
023import org.apache.commons.jxpath.ri.parser.TokenMgrError;
024import org.apache.commons.jxpath.ri.parser.XPathParser;
025
026/**
027 * XPath parser
028 *
029 * @author Dmitri Plotnikov
030 * @version $Revision: 652845 $ $Date: 2008-05-02 13:46:46 -0400 (Fri, 02 May 2008) $
031 */
032public class Parser {
033
034    private static XPathParser parser = new XPathParser(new StringReader(""));
035
036    /**
037     * Parses the XPath expression. Throws a JXPathException in case
038     * of a syntax error.
039     * @param expression to parse
040     * @param compiler the compiler
041     * @return parsed Object
042     */
043    public static Object parseExpression(
044        String expression,
045        Compiler compiler) {
046        synchronized (parser) {
047            parser.setCompiler(compiler);
048            Object expr = null;
049            try {
050                parser.ReInit(new StringReader(expression));
051                expr = parser.parseExpression();
052            }
053            catch (TokenMgrError e) {
054                throw new JXPathInvalidSyntaxException(
055                    "Invalid XPath: '"
056                        + addEscapes(expression)
057                        + "'. Invalid symbol '"
058                        + addEscapes(String.valueOf(e.getCharacter()))
059                        + "' "
060                        + describePosition(expression, e.getPosition()));
061            }
062            catch (ParseException e) {
063                throw new JXPathInvalidSyntaxException(
064                    "Invalid XPath: '"
065                        + addEscapes(expression)
066                        + "'. Syntax error "
067                        + describePosition(
068                            expression,
069                            e.currentToken.beginColumn));
070            }
071            return expr;
072        }
073    }
074
075    /**
076     * Describe a parse position.
077     * @param expression to parse
078     * @param position parse position
079     * @return String
080     */
081    private static String describePosition(String expression, int position) {
082        if (position <= 0) {
083            return "at the beginning of the expression";
084        }
085        if (position >= expression.length()) {
086            return "- expression incomplete";
087        }
088        return "after: '"
089            + addEscapes(expression.substring(0, position)) + "'";
090    }
091
092    /**
093     * Add escapes to the specified String.
094     * @param string incoming String
095     * @return String
096     */
097    private static String addEscapes(String string) {
098        // Piggy-back on the code generated by JavaCC
099        return TokenMgrError.addEscapes(string);
100    }
101}