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Java > Open Source Codes > org > apache > commons > jxpath > ri > Parser


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.jxpath.ri;
17
18 import java.io.StringReader JavaDoc;
19
20 import org.apache.commons.jxpath.JXPathException;
21 import org.apache.commons.jxpath.ri.parser.ParseException;
22 import org.apache.commons.jxpath.ri.parser.TokenMgrError;
23 import org.apache.commons.jxpath.ri.parser.XPathParser;
24
25 /**
26  * XPath parser
27  *
28  * @author Dmitri Plotnikov
29  * @version $Revision: 1.8 $ $Date: 2004/02/29 14:17:45 $
30  */
31 public class Parser {
32
33     private static XPathParser parser = new XPathParser(new StringReader JavaDoc(""));
34
35     /**
36      * Parses the XPath expression. Throws a JXPathException in case
37      * of a syntax error.
38      */
39     public static Object JavaDoc parseExpression(
40         String JavaDoc expression,
41         Compiler JavaDoc compiler)
42     {
43         synchronized (parser) {
44             parser.setCompiler(compiler);
45             Object JavaDoc expr = null;
46             try {
47                 parser.ReInit(new StringReader JavaDoc(expression));
48                 expr = parser.parseExpression();
49             }
50             catch (TokenMgrError e) {
51                 throw new JXPathException(
52                     "Invalid XPath: '"
53                         + addEscapes(expression)
54                         + "'. Invalid symbol '"
55                         + addEscapes(String.valueOf(e.getCharacter()))
56                         + "' "
57                         + describePosition(expression, e.getPosition()));
58             }
59             catch (ParseException e) {
60                 throw new JXPathException(
61                     "Invalid XPath: '"
62                         + addEscapes(expression)
63                         + "'. Syntax error "
64                         + describePosition(
65                             expression,
66                             e.currentToken.beginColumn));
67             }
68             return expr;
69         }
70     }
71
72     private static String JavaDoc describePosition(String JavaDoc expression, int position) {
73         if (position <= 0) {
74             return "at the beginning of the expression";
75         }
76         else if (position >= expression.length()) {
77             return "- expression incomplete";
78         }
79         else {
80             return "after: '"
81                 + addEscapes(expression.substring(0, position)) + "'";
82         }
83     }
84
85     private static String JavaDoc addEscapes(String JavaDoc string) {
86         // Piggy-back on the code generated by JavaCC
87 return TokenMgrError.addEscapes(string);
88     }
89 }
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