Commons JXPath example source code file (Parser.java)

This example Commons JXPath source code file (Parser.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons JXPath tags/keywords

invalid, invalid, io, jxpathinvalidsyntaxexception, jxpathinvalidsyntaxexception, object, object, parseexception, string, string, stringreader, syntax, tokenmgrerror, xpath, xpathparser

The Commons JXPath Parser.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.jxpath.ri;

import java.io.StringReader;

import org.apache.commons.jxpath.JXPathInvalidSyntaxException;
import org.apache.commons.jxpath.ri.parser.ParseException;
import org.apache.commons.jxpath.ri.parser.TokenMgrError;
import org.apache.commons.jxpath.ri.parser.XPathParser;

/**
 * XPath parser
 *
 * @author Dmitri Plotnikov
 * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
 */
public class Parser {

    private static XPathParser parser = new XPathParser(new StringReader(""));

    /**
     * Parses the XPath expression. Throws a JXPathException in case
     * of a syntax error.
     * @param expression to parse
     * @param compiler the compiler
     * @return parsed Object
     */
    public static Object parseExpression(
        String expression,
        Compiler compiler) {
        synchronized (parser) {
            parser.setCompiler(compiler);
            Object expr = null;
            try {
                parser.ReInit(new StringReader(expression));
                expr = parser.parseExpression();
            }
            catch (TokenMgrError e) {
                throw new JXPathInvalidSyntaxException(
                    "Invalid XPath: '"
                        + addEscapes(expression)
                        + "'. Invalid symbol '"
                        + addEscapes(String.valueOf(e.getCharacter()))
                        + "' "
                        + describePosition(expression, e.getPosition()));
            }
            catch (ParseException e) {
                throw new JXPathInvalidSyntaxException(
                    "Invalid XPath: '"
                        + addEscapes(expression)
                        + "'. Syntax error "
                        + describePosition(
                            expression,
                            e.currentToken.beginColumn));
            }
            return expr;
        }
    }

    /**
     * Describe a parse position.
     * @param expression to parse
     * @param position parse position
     * @return String
     */
    private static String describePosition(String expression, int position) {
        if (position <= 0) {
            return "at the beginning of the expression";
        }
        if (position >= expression.length()) {
            return "- expression incomplete";
        }
        return "after: '"
            + addEscapes(expression.substring(0, position)) + "'";
    }

    /**
     * Add escapes to the specified String.
     * @param string incoming String
     * @return String
     */
    private static String addEscapes(String string) {
        // Piggy-back on the code generated by JavaCC
        return TokenMgrError.addEscapes(string);
    }
}