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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 DRIVER_PROPERTY = "org.saxpath.driver";
85  
86      /*** The default driver to use if none is configured. */
87      protected static final String 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 className = null;
106 
107         try
108         {
109             className = System.getProperty( DRIVER_PROPERTY );
110         }
111         catch (SecurityException 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 className) throws SAXPathException
140     {
141         Class 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 e)
164         {
165             throw new SAXPathException( e );
166         }
167 
168         try
169         {
170             reader = (XPathReader) readerClass.newInstance();
171         }
172         catch (IllegalAccessException e)
173         {
174             throw new SAXPathException( e );
175         }
176         catch (InstantiationException 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 }