contentmetadatafactory.java

jxta-cms-src-2.4.zip 是官网上的比较稳定的CMS源代码。目前是最稳定的高版本。

/*
 * Copyright (c) 2001 Sun Microsystems, Inc.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *       Sun Microsystems, Inc. for Project JXTA."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact Project JXTA at http://www.jxta.org.
 *
 * 5. Products derived from this software may not be called "JXTA",
 *    nor may "JXTA" appear in their name, without prior written
 *    permission of Sun.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 APACHE SOFTWARE FOUNDATION OR
 * ITS 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 Project JXTA.  For more
 * information on Project JXTA, please see
 * <http://www.jxta.org/>.
 *
 * This license is based on the BSD license adopted by the Apache Foundation.
 *
 * $Id: ContentMetadataFactory.java,v 1.4 2006/02/07 20:43:51 bondolo Exp $
 *
 */

package net.jxta.share.metadata;

import net.jxta.document.StructuredDocument;
import net.jxta.document.Element;
import org.apache.log4j.Logger;
import org.apache.log4j.Level;
import java.util.Hashtable;

/** A factory class used by ContentAdvertisementImpl to ensure that a metadata
 * element is parsed and stored by the ContentMetadata object that is most
 * specific to the element's scheme and content type.
 *@see net.jxta.share.ContentAdvertisementImpl
 *@version $Revision: 1.4 $
 *@author $Author: bondolo $
 */
public class ContentMetadataFactory {
    private final static transient Logger LOG = Logger.getLogger(ContentMetadataFactory.class.getName());

    private static ContentMetadataConstructor genericConstructor = null;
    
    private static Hashtable registry = new Hashtable();

    //constructor registrations can be hardcoded here
    static {
	registerClass(Description.SN_DESCRIPTION,
		      Description.DESCRIPTION_CONTENT_TYPE,
		      Description.getConstructor());
	
	registerClass(Keywords.SN_KEYWORDS, Keywords.KEYWORDS_CONTENT_TYPE,
					     Keywords.getConstructor());
	
    }

    /**Get the ContentMetadataConstructor that is registered for use with
     * metadata of a certain scheme and content type.
     *@exception SchemeNotFoundException if no constructor is registered for
     * the given scheme and content type.
     */
    public static ContentMetadataConstructor getConstructor(String scheme_name,
							  String content_type)
	throws SchemeNotFoundException {
	ContentMetadataConstructor constructor = null;
	constructor =
	    (ContentMetadataConstructor)registry.get(scheme_name+content_type);
	if(constructor == null)
	    throw new SchemeNotFoundException();
	return constructor;
    }

    /**Create a new ContentMetadata instance from a metadata element using the
     * most appropriate ContentMetadataConstructor.  If no specialized
     * ContentMetadataConstructor can be found, a the generic constructor is
     * used.  If the generic constructor fails, a ContentMetadataImpl
     * representation of metadataEl is returned.
     * @see ContentMetadataImpl
     */
    public static ContentMetadata newInstance(Element metadataEl) {
	ContentMetadata result = new ContentMetadataImpl(metadataEl);
	ContentMetadataConstructor constructor
	    =(ContentMetadataConstructor)registry.get(result.getName() +
						      result.getContentType());
	
	boolean registryFailed = false;
	if(constructor != null) {
	    try {
		result = constructor.newInstance(metadataEl);
	    }catch(IllegalArgumentException iae) {
		registryFailed = true;
		if(LOG.isEnabledFor(Level.INFO))
		    LOG.info("instanciation failed: "+iae
			     +"\nconstructor class: "
			     + constructor.getClass().getName()
			     + "\nscheme name:" + result.getName()
			     + "\ncontent type:" + result.getContentType());
	    }
	}else {
	    registryFailed = true;
	    if(LOG.isDebugEnabled()) {
		LOG.debug("no constructor registered for metadata of scheme '"
			  + result.getName() + "' and content type '"
			  + result.getContentType() + "'");
	    }
	}
	if(registryFailed && genericConstructor != null) {
	    try {
		result = genericConstructor.newInstance(metadataEl);
	    }catch(IllegalArgumentException iae) {
		//result will still = new ContentMetadataImpl(metadataEl);
	    }
	}
	return result;
    }
    
    /**Register the constructor that will be used to parse metadata elements 
     * with a certain scheme and content type.
     */
    public static void registerClass(String scheme_name, String content_type
				     ,ContentMetadataConstructor constructor) {
	registry.put(scheme_name+content_type, constructor);
    }

    /**Select the constructor that will be used if no more specific
     * constructor can be found or used to parse a metadata element.
     */
    public static void registerGenericClass(ContentMetadataConstructor
					    constructor) {
	genericConstructor = constructor;
    }
}