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