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Java > Open Source Codes > org > jaxen > saxpath > helpers > XPathReaderFactory


1 /*
2  * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/saxpath/helpers/XPathReaderFactory.java,v 1.6 2005/06/14 15:13:07 elharo Exp $
3  * $Revision: 1.6 $
4  * $Date: 2005/06/14 15:13:07 $
5  *
6  * ====================================================================
7  *
8  * Copyright (C) 2000-2002 bob mcwhirter & James Strachan.
9  * All rights reserved.
10  *
11  * Redistribution and use in source and binary forms, with or without
12  * modification, are permitted provided that the following conditions
13  * are met:
14  *
15  * 1. Redistributions of source code must retain the above copyright
16  * notice, this list of conditions, and the following disclaimer.
17  *
18  * 2. Redistributions in binary form must reproduce the above copyright
19  * notice, this list of conditions, and the disclaimer that follows
20  * these conditions in the documentation and/or other materials
21  * provided with the distribution.
22  *
23  * 3. The name "Jaxen" must not be used to endorse or promote products
24  * derived from this software without prior written permission. For
25  * written permission, please contact license@jaxen.org.
26  *
27  * 4. Products derived from this software may not be called "Jaxen", nor
28  * may "Jaxen" appear in their name, without prior written permission
29  * from the Jaxen Project Management (pm@jaxen.org).
30  *
31  * In addition, we request (but do not require) that you include in the
32  * end-user documentation provided with the redistribution and/or in the
33  * software itself an acknowledgement equivalent to the following:
34  * "This product includes software developed by the
35  * Jaxen Project (http://www.jaxen.org/)."
36  * Alternatively, the acknowledgment may be graphical using the logos
37  * available at http://www.jaxen.org/
38  *
39  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
40  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
41  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
42  * DISCLAIMED. IN NO EVENT SHALL THE Jaxen AUTHORS OR THE PROJECT
43  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
44  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
45  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
46  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
47  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
48  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
49  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50  * SUCH DAMAGE.
51  *
52  * ====================================================================
53  * This software consists of voluntary contributions made by many
54  * individuals on behalf of the Jaxen Project and was originally
55  * created by bob mcwhirter <bob@werken.com> and
56  * James Strachan <jstrachan@apache.org>. For more information on the
57  * Jaxen Project, please see <http://www.jaxen.org/>.
58  *
59  * $Id: XPathReaderFactory.java,v 1.6 2005/06/14 15:13:07 elharo Exp $
60  */
61
62
63
64
65 package org.jaxen.saxpath.helpers;
66
67 import org.jaxen.saxpath.SAXPathException;
68 import org.jaxen.saxpath.XPathReader;
69
70 /** Create an {@link org.jaxen.saxpath.XPathReader} from
71  * either a system property, or a named class.
72  *
73  * <p>
74  * Similar to the SAX API, the <code>XPathReaderFactory</code>
75  * can create an <code>XPathReader</code> from a name of a
76  * class passed in directly, or by inspecting the system
77  * property <code>org.saxpath.driver</code>.
78  *
79  * @author bob mcwhirter (bob@werken.com)
80  */
81 public class XPathReaderFactory
82 {
83     /** The <code>org.saxpath.driver</code> property name. */
84     public static final String JavaDoc DRIVER_PROPERTY = "org.saxpath.driver";
85
86     /** The default driver to use if none is configured. */
87     protected static final String JavaDoc DEFAULT_DRIVER = "org.jaxen.saxpath.base.XPathReader";
88     
89     private XPathReaderFactory() {}
90     
91     
92     /** Create an <code>XPathReader</code> using the value of
93      * the <code>org.saxpath.driver</code> system property.
94      *
95      * @return an instance of the <code>XPathReader</code> specified
96      * by the <code>org.saxpath.driver</code> property
97      *
98      * @throws SAXPathException if the property is not set, or if
99      * the class can not be instantiated for some reason,
100      * or if the class doesn't implement the <code>XPathReader</code>
101      * interface
102      */
103     public static XPathReader createReader() throws SAXPathException
104     {
105         String JavaDoc className = null;
106
107         try
108         {
109             className = System.getProperty( DRIVER_PROPERTY );
110         }
111         catch (SecurityException JavaDoc e)
112         {
113             // we'll use the default
114 }
115
116         if ( className == null
117              ||
118              className.length() == 0 )
119         {
120             className = DEFAULT_DRIVER;
121         }
122
123         return createReader( className );
124     }
125     
126     /** Create an <code>XPathReader</code> using the passed
127      * in class name.
128      *
129      * @param className the name of the class that implements
130      * the <code>XPathReader</code> interface.
131      *
132      * @return an XPathReader
133      *
134      * @throws SAXPathException if the class cannot be
135      * instantiated for some reason, or if the
136      * class doesn't implement the <code>XPathReader</code>
137      * interface
138      */
139     public static XPathReader createReader(String JavaDoc className) throws SAXPathException
140     {
141         Class JavaDoc readerClass = null;
142         XPathReader reader = null;
143
144         try
145         {
146             // Use the full version of Class.forName(), so as to
147 // work better in sandboxed environments, such as
148 // servlet containers and applets.
149
150             readerClass = Class.forName( className,
151                                          true,
152                                          XPathReaderFactory.class.getClassLoader() );
153             
154             // Double-check that it's actually the right kind of class
155 // before attempting instantiation.
156
157             if ( ! XPathReader.class.isAssignableFrom( readerClass ) )
158             {
159                 throw new SAXPathException( "Class [" + className
160                   + "] does not implement the org.jaxen.saxpath.XPathReader interface." );
161             }
162         }
163         catch (ClassNotFoundException JavaDoc e)
164         {
165             throw new SAXPathException( e );
166         }
167
168         try
169         {
170             reader = (XPathReader) readerClass.newInstance();
171         }
172         catch (IllegalAccessException JavaDoc e)
173         {
174             throw new SAXPathException( e );
175         }
176         catch (InstantiationException JavaDoc e)
177         {
178             throw new SAXPathException( e );
179         }
180
181         if ( reader == null )
182         {
183             throw new SAXPathException( "Unable to create XPathReader" );
184         }
185         
186         return reader;
187     }
188 }
189
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