    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     */
    017    package org.apache.commons.jxpath.ri;
    018
    019    import java.io.StringReader;
    020
    021    import org.apache.commons.jxpath.JXPathInvalidSyntaxException;
    022    import org.apache.commons.jxpath.ri.parser.ParseException;
    023    import org.apache.commons.jxpath.ri.parser.TokenMgrError;
    024    import 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 12:46:46 -0500 (Fri, 02 May 2008) $
    031     */
    032    public 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    }