001/* ContentHandler.java -- Abstract class for handling content from URL's
002   Copyright (C) 1998, 1999, 2000, 2001, 2003 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038package java.net;
039
040import 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  */
060public 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