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1   /*
2    * $Header$
3    * $Revision: 1193 $
4    * $Date: 2006-09-15 13:41:38 -0700 (Fri, 15 Sep 2006) $
5    *
6    * ====================================================================
7    *
8    * Copyright 2000-2002 bob mcwhirter & James Strachan.
9    * All rights reserved.
10   *
11   *
12   * Redistribution and use in source and binary forms, with or without
13   * modification, are permitted provided that the following conditions are
14   * met:
15   * 
16   *   * Redistributions of source code must retain the above copyright
17   *     notice, this list of conditions and the following disclaimer.
18   * 
19   *   * Redistributions in binary form must reproduce the above copyright
20   *     notice, this list of conditions and the following disclaimer in the
21   *     documentation and/or other materials provided with the distribution.
22   * 
23   *   * Neither the name of the Jaxen Project nor the names of its
24   *     contributors may be used to endorse or promote products derived 
25   *     from this software without specific prior written permission.
26   * 
27   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
28   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
29   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
30   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
31   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
32   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
33   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
34   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
35   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
36   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
37   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
38   *
39   * ====================================================================
40   * This software consists of voluntary contributions made by many
41   * individuals on behalf of the Jaxen Project and was originally
42   * created by bob mcwhirter <bob@werken.com> and
43   * James Strachan <jstrachan@apache.org>.  For more information on the
44   * Jaxen Project, please see <http://www.jaxen.org/>.
45   *
46   * $Id: XPathReaderFactory.java 1193 2006-09-15 20:41:38Z elharo $
47   */
48  
49  
50  
51  
52  package org.jaxen.saxpath.helpers;
53  
54  import org.jaxen.saxpath.SAXPathException;
55  import org.jaxen.saxpath.XPathReader;
56  
57  /** Create an {@link org.jaxen.saxpath.XPathReader} from
58   *  either a system property, or a named class.
59   *
60   *  <p>
61   *  Similar to the SAX API, the <code>XPathReaderFactory</code>
62   *  can create an <code>XPathReader</code> from a name of a
63   *  class passed in directly, or by inspecting the system
64   *  property <code>org.saxpath.driver</code>.
65   *
66   *  @author bob mcwhirter (bob@werken.com)
67   */
68  public class XPathReaderFactory
69  {
70      /** The <code>org.saxpath.driver</code> property name. */
71      public static final String DRIVER_PROPERTY = "org.saxpath.driver";
72  
73      /** The default driver to use if none is configured. */
74      protected static final String DEFAULT_DRIVER = "org.jaxen.saxpath.base.XPathReader";
75      
76      private XPathReaderFactory() {}
77      
78      
79      /** Create an <code>XPathReader</code> using the value of
80       *  the <code>org.saxpath.driver</code> system property.
81       *
82       *  @return an instance of the <code>XPathReader</code> specified
83       *          by the <code>org.saxpath.driver</code> property
84       *
85       *  @throws SAXPathException if the property is  not set, or if
86       *          the class can not be instantiated for some reason,
87       *          or if the class doesn't implement the <code>XPathReader</code>
88       *          interface
89       */
90      public static XPathReader createReader() throws SAXPathException
91      {
92          String className = null;
93  
94          try
95          {
96              className = System.getProperty( DRIVER_PROPERTY );
97          }
98          catch (SecurityException e)
99          {
100             // we'll use the default
101         }
102 
103         if ( className == null
104              ||
105              className.length() == 0 )
106         {
107             className = DEFAULT_DRIVER;
108         }
109 
110         return createReader( className );
111     }
112     
113     /** Create an <code>XPathReader</code> using the passed
114      *  in class name.
115      *
116      *  @param className the name of the class that implements
117      *         the <code>XPathReader</code> interface.
118      * 
119      *  @return an XPathReader
120      *
121      *  @throws SAXPathException if the class cannot be
122      *          instantiated for some reason, or if the
123      *          class doesn't implement the <code>XPathReader</code>
124      *          interface
125      */
126     public static XPathReader createReader(String className) throws SAXPathException
127     {
128         Class readerClass  = null;
129         XPathReader reader = null;
130 
131         try
132         {
133             // Use the full version of Class.forName(), so as to
134             // work better in sandboxed environments, such as
135             // servlet containers and applets.
136 
137             readerClass = Class.forName( className,
138                                          true,
139                                          XPathReaderFactory.class.getClassLoader() );
140             
141             // Double-check that it's actually the right kind of class
142             // before attempting instantiation.
143             
144             if ( ! XPathReader.class.isAssignableFrom( readerClass ) )
145             {
146                 throw new SAXPathException( "Class [" + className 
147                   + "] does not implement the org.jaxen.saxpath.XPathReader interface." );
148             }
149         }
150         catch (ClassNotFoundException e)
151         {
152             throw new SAXPathException( e );
153         }
154 
155         try
156         {
157             reader = (XPathReader) readerClass.newInstance();
158         }
159         catch (IllegalAccessException e)
160         {
161             throw new SAXPathException( e );
162         }
163         catch (InstantiationException e)
164         {
165             throw new SAXPathException( e );
166         }
167         
168         return reader;
169     }
170 }