xpathreaderfactory.java

XML的解析、编译、查询等技术的JAVA源代码。

/*
 * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/saxpath/helpers/XPathReaderFactory.java,v 1.9 2006/09/15 20:41:38 elharo Exp $
 * $Revision: 1.9 $
 * $Date: 2006/09/15 20:41:38 $
 *
 * ====================================================================
 *
 * 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 <[e-mail]> and
 * James Strachan <[e-mail]>.  For more information on the
 * Jaxen Project, please see <http://www.jaxen.org/>.
 *
 * $Id: XPathReaderFactory.java,v 1.9 2006/09/15 20:41:38 elharo Exp $
 */




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 ([e-mail])
 */
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;
    }
}