001    /* ContentHandler.java -- Abstract class for handling content from URL's
002       Copyright (C) 1998, 1999, 2000, 2001, 2003 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.net;
039    
040    import java.io.IOException;
041    
042    /**
043     * Written using on-line Java Platform 1.2 API Specification, as well
044     * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
045     * Status:  Believed complete and correct.
046     */
047    
048    /**
049      * This is an abstract class that is the superclass for classes that read
050      * objects from URL's.  Calling the <code>getContent()</code> method in the
051      * <code>URL</code> class or the <code>URLConnection</code> class will cause
052      * an instance of a subclass of <code>ContentHandler</code> to be created for
053      * the MIME type of the object being downloaded from the URL.  Thus, this
054      * class is seldom needed by applications/applets directly, but only
055      * indirectly through methods in other classes.
056      *
057      * @author Aaron M. Renn (arenn@urbanophile.com)
058      * @author Warren Levy (warrenl@cygnus.com)
059      */
060    public abstract class ContentHandler
061    {
062      /*
063       * Constructors
064       */
065    
066      /**
067        * Default, no-argument constructor.
068        */
069      public ContentHandler()
070      {
071      }
072    
073      /*
074       * Instance Methods
075       */
076    
077      /**
078        * This method reads from the <code>InputStream</code> of the passed in URL
079        * connection and uses the data downloaded to create an <code>Object</code>
080        * represening the content.  For example, if the URL is pointing to a GIF
081        * file, this method might return an <code>Image</code> object.  This method
082        * must be implemented by subclasses.
083        *
084        * @param urlc A <code>URLConnection</code> object to read data from.
085        *
086        * @return An object representing the data read
087        *
088        * @exception IOException If an error occurs
089        */
090      public abstract Object getContent(URLConnection urlc)
091        throws IOException;
092    
093      /**
094        * This method reads from the <code>InputStream</code> of the passed in URL
095        * connection and uses the data downloaded to create an <code>Object</code>
096        * represening the content.  For example, if the URL is pointing to a GIF
097        * file, this method might return an <code>Image</code> object.  This method
098        * must be implemented by subclasses.  This method uses the list of
099        * supplied classes as candidate types.  If the data read doesn't match
100        * any of the supplied type, <code>null</code> is returned.
101        *
102        * @param urlc A <code>URLConnection</code> object to read data from.
103        * @param classes An array of types of objects that are candidate types
104        * for the data to be read.
105        *
106        * @return An object representing the data read, or <code>null</code>
107        * if the data does not match any of the candidate types.
108        *
109        * @exception IOException If an error occurs
110        *
111        * @since 1.3
112        */
113      public Object getContent(URLConnection urlc, Class[] classes)
114        throws IOException
115      {
116        Object obj = getContent(urlc);
117    
118        for (int i = 0; i < classes.length; i++)
119          {
120            if (classes[i].isInstance(obj))
121              return obj;
122          }
123    
124        return null;
125      }
126    } // class ContentHandler