content: /*
   * $Header$
   * $Revision$
   * $Date$
   *
   * ====================================================================
   *
   * Copyright 2000-2002 bob mcwhirter & James Strachan.
   * All rights reserved.
   *
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   * 
   *   * Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   * 
   *   * Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   * 
   *   * Neither the name of the Jaxen Project nor the names of its
   *     contributors may be used to endorse or promote products derived 
   *     from this software without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * ====================================================================
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Jaxen Project and was originally
   * created by bob mcwhirter <bob@werken.com> and
   * James Strachan <jstrachan@apache.org>.  For more information on the
   * Jaxen Project, please see <http://www.jaxen.org/>.
   *
   * $Id$
   */
  
  
  
  
  package org.jaxen.saxpath.helpers;
  
  import org.jaxen.saxpath.SAXPathException;
  import org.jaxen.saxpath.XPathReader;
  
  /** Create an {@link org.jaxen.saxpath.XPathReader} from
   *  either a system property, or a named class.
   *
   *  <p>
   *  Similar to the SAX API, the <code>XPathReaderFactory</code>
   *  can create an <code>XPathReader</code> from a name of a
   *  class passed in directly, or by inspecting the system
   *  property <code>org.saxpath.driver</code>.
   *
   *  @author bob mcwhirter (bob@werken.com)
   */
  public class XPathReaderFactory
  {
      /** The <code>org.saxpath.driver</code> property name. */
      public static final String DRIVER_PROPERTY = "org.saxpath.driver";
  
      /** The default driver to use if none is configured. */
      protected static final String DEFAULT_DRIVER = "org.jaxen.saxpath.base.XPathReader";
      
      private XPathReaderFactory() {}
      
      
      /** Create an <code>XPathReader</code> using the value of
       *  the <code>org.saxpath.driver</code> system property.
       *
       *  @return an instance of the <code>XPathReader</code> specified
       *          by the <code>org.saxpath.driver</code> property
       *
       *  @throws SAXPathException if the property is  not set, or if
       *          the class can not be instantiated for some reason,
       *          or if the class doesn't implement the <code>XPathReader</code>
       *          interface
       */
      public static XPathReader createReader() throws SAXPathException
      {
          String className = null;
  
          try
          {
              className = System.getProperty( DRIVER_PROPERTY );
          }
          catch (SecurityException e)
          {
              // we'll use the default
          }
  
          if ( className == null
               ||
               className.length() == 0 )
          {
              className = DEFAULT_DRIVER;
          }
  
          return createReader( className );
      }
      
      /** Create an <code>XPathReader</code> using the passed
       *  in class name.
       *
       *  @param className the name of the class that implements
       *         the <code>XPathReader</code> interface.
       * 
       *  @return an XPathReader
       *
       *  @throws SAXPathException if the class cannot be
       *          instantiated for some reason, or if the
       *          class doesn't implement the <code>XPathReader</code>
       *          interface
       */
      public static XPathReader createReader(String className) throws SAXPathException
      {
          Class readerClass  = null;
          XPathReader reader = null;
  
          try
          {
              // Use the full version of Class.forName(), so as to
              // work better in sandboxed environments, such as
              // servlet containers and applets.
  
              readerClass = Class.forName( className,
                                           true,
                                           XPathReaderFactory.class.getClassLoader() );
              
              // Double-check that it's actually the right kind of class
              // before attempting instantiation.
              
              if ( ! XPathReader.class.isAssignableFrom( readerClass ) )
              {
                  throw new SAXPathException( "Class [" + className 
                    + "] does not implement the org.jaxen.saxpath.XPathReader interface." );
              }
          }
          catch (ClassNotFoundException e)
          {
              throw new SAXPathException( e );
          }
  
          try
          {
              reader = (XPathReader) readerClass.newInstance();
          }
          catch (IllegalAccessException e)
          {
              throw new SAXPathException( e );
          }
          catch (InstantiationException e)
          {
              throw new SAXPathException( e );
          }
          
          return reader;
      }
  }
  