View Javadoc

1   /*
2    * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/saxpath/helpers/XPathReaderFactory.java,v 1.4 2005/04/09 14:03:38 elharo Exp $
3    * $Revision: 1.4 $
4    * $Date: 2005/04/09 14:03:38 $
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 1.4 2005/04/09 14:03:38 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      /*** Should the default driver be used */
90      private static boolean USE_DEFAULT = true;
91      
92      
93      /*** Create an <code>XPathReader</code> using the value of
94       *  the <code>org.saxpath.driver</code> system property.
95       *
96       *  @return an instance of the <code>XPathReader</code> specified
97       *          by the <code>org.saxpath.driver</code> property
98       *
99       *  @throws SAXPathException if the property is  not set, or if
100      *          the class can not be instantiated for some reason,
101      *          or if the class doesn't implement the <code>XPathReader</code>
102      *          interface
103      */
104     public static XPathReader createReader() throws SAXPathException
105     {
106         String className = null;
107 
108         boolean securityException = false;
109 
110         try
111         {
112             className = System.getProperty( DRIVER_PROPERTY );
113         }
114         catch (SecurityException e)
115         {
116             securityException = true;
117         }
118 
119         if ( className == null
120              ||
121              className.length() == 0 )
122         {
123             if ( USE_DEFAULT )
124             {
125                 className = DEFAULT_DRIVER;
126             }
127             else
128             {
129                 if ( securityException )
130                 {
131                     throw new SAXPathException( "Reading of property " + DRIVER_PROPERTY + " disallowed." );
132                 }
133                 else
134                 {
135                     throw new SAXPathException( "Property " + DRIVER_PROPERTY + " not set" );
136                 }
137             }
138         }
139 
140         return createReader( className );
141     }
142     
143     /*** Create an <code>XPathReader</code> using the passed
144      *  in class name.
145      *
146      *  @param className the name of the class that implements
147      *         the <code>XPathReader</code> interface.
148      *
149      *  @throws SAXPathException if the class can not be
150      *          instantiated for some reason, or if the
151      *          class doesn't implement the <code>XPathReader</code>
152      *          interface
153      */
154     public static XPathReader createReader(String className) throws SAXPathException
155     {
156         Class readerClass  = null;
157         XPathReader reader = null;
158 
159         try
160         {
161             // Use the full version of Class.forName(), so as to
162             // work better in sandboxed environments, such as
163             // Servlet contains, and applets.
164 
165             readerClass = Class.forName( className,
166                                          true,
167                                          XPathReaderFactory.class.getClassLoader() );
168             
169             // Double-check that it's actually the right kind of class
170             // before attempting instantiation.
171             
172             if ( ! XPathReader.class.isAssignableFrom( readerClass ) )
173             {
174                 throw new SAXPathException( "Class [" + className 
175                   + "] does not implement the org.jaxen.saxpath.XPathReader interface." );
176             }
177         }
178         catch (ClassNotFoundException e)
179         {
180             throw new SAXPathException( e );
181         }
182 
183         try
184         {
185             reader = (XPathReader) readerClass.newInstance();
186         }
187         catch (IllegalAccessException e)
188         {
189             throw new SAXPathException( e );
190         }
191         catch (InstantiationException e)
192         {
193             throw new SAXPathException( e );
194         }
195 
196         if ( reader == null )
197         {
198             throw new SAXPathException( "Unable to create XPathReader" );
199         }
200         
201         return reader;
202     }
203 }