extendableadvertisement.java

jxta_src_2.41b jxta 2.41b 最新版源码 from www.jxta.org

/*
 * $Id: ExtendableAdvertisement.java,v 1.2 2004/04/23 20:03:12 bondolo Exp $
 ********************
 *
 * Copyright (c) 2001-2003 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
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 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    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
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 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * ====================================================================
 *
 * 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.
 ********************
 */

package net.jxta.document;

/**
 *  Extendable advertisements provide features for allowing inheritance of
 *  advertisement types. The core and standard JXTA advertisements all allow
 *  extension by extending this class.
 *
 *  @see net.jxta.document.Advertisement
 *  @see net.jxta.document.AdvertisementFactory
 *  @see net.jxta.document.Document
 *  @see net.jxta.document.MimeMediaType
 *
 **/
public abstract class ExtendableAdvertisement extends Advertisement {
    
    /**
     *  Returns the base type of this advertisement hierarchy. Typically, only
     *  the most basic advertisement of a type will implement this method and
     *  declare it as <code>final</code>.
     *
     *  @return String the base type of advertisements in this hierarchy.
     **/
    public abstract String getBaseAdvType();
    
    /**
     *  Process an individual element from the document during parse. Normally,
     *  implementations will allow the base advertisments a chance to handle the
     *  element before attempting ot handle the element themselves. ie.
     *
     *  <p/><pre><code>
     *  protected boolean handleElement( Element elem ) {
     *
     *      if ( super.handleElement() ) {
     *           // it's been handled.
     *           return true;
     *           }
     *
     *      <i>... handle elements here ...</i>
     *
     *      // we don't know how to handle the element
     *      return false;
     *      }
     *  </code></pre>
     *
     *  @param elem the element to be processed.
     *  @return true if the element was recognized, otherwise false.
     **/
    protected boolean handleElement( Element elem ) {
        // we don't handle any elements.
        return false;
    }
    
    /**
     * {@inheritDoc}
     *
     * <p/>We don't have any content to add, just build the document instance
     * and return it to implementations that actually do something with it.
     **/
    public Document getDocument( MimeMediaType encodeAs ) {
        Document adv = StructuredDocumentFactory.newStructuredDocument( encodeAs, getBaseAdvType() );
        
        if( adv instanceof XMLDocument ) {
            XMLDocument xmlAdv = (XMLDocument) adv;
            
            xmlAdv.addAttribute( "xmlns:jxta", "http://jxta.org" );
//            xmlAdv.addAttribute( "xml:space", "preserve" );
            if( !getBaseAdvType().equals( getAdvType() ) ) {
                xmlAdv.addAttribute( "type", getAdvType() );
            }
        }
        
        return adv;
    }
}