1 /*
2 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.net;
27
28 import java.io.IOException;
29
30 /**
31 * The abstract class {@code ContentHandler} is the superclass
32 * of all classes that read an {@code Object} from a
33 * {@code URLConnection}.
34 * <p>
35 * An application does not generally call the
36 * {@code getContent} method in this class directly. Instead, an
37 * application calls the {@code getContent} method in class
38 * {@code URL} or in {@code URLConnection}.
39 * The application's content handler factory (an instance of a class that
40 * implements the interface {@code ContentHandlerFactory} set
41 * up by a call to {@code setContentHandler}) is
42 * called with a {@code String} giving the MIME type of the
43 * object being received on the socket. The factory returns an
44 * instance of a subclass of {@code ContentHandler}, and its
45 * {@code getContent} method is called to create the object.
46 * <p>
47 * If no content handler could be {@linkplain URLConnection#getContent() found},
48 * URLConnection will look for a content handler in a user-definable set of places.
49 * Users can define a vertical-bar delimited set of class prefixes
50 * to search through by defining the <i>{@link java.net.URLConnection#contentPathProp}</i>
51 * property. The class name must be of the form:
52 * <blockquote>
53 * <i>{package-prefix}.{major}.{minor}</i>
54 * <p>
55 * where <i>{major}.{minor}</i> is formed by taking the
56 * content-type string, replacing all slash characters with a
57 * {@code period} ('.'), and all other non-alphanumeric characters
58 * with the underscore character '{@code _}'. The alphanumeric
59 * characters are specifically the 26 uppercase ASCII letters
60 * '{@code A}' through '{@code Z}', the 26 lowercase ASCII
61 * letters '{@code a}' through '{@code z}', and the 10 ASCII
62 * digits '{@code 0}' through '{@code 9}'.
63 * <p>
64 * e.g.
65 * YoyoDyne.experimental.text.plain
66 * </blockquote>
67 * If no user-defined content handler is found, then the system
68 * tries to load a specific <i>content-type</i> handler from one
69 * of the built-in handlers, if one exists.
70 * <p>
71 * If the loading of the content handler class would be performed by
72 * a classloader that is outside of the delegation chain of the caller,
73 * the JVM will need the RuntimePermission "getClassLoader".
74 *
75 * @author James Gosling
76 * @see java.net.ContentHandler#getContent(java.net.URLConnection)
77 * @see java.net.ContentHandlerFactory
78 * @see java.net.URL#getContent()
79 * @see java.net.URLConnection
80 * @see java.net.URLConnection#getContent()
81 * @see java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
82 * @since 1.0
83 */
84 abstract public class ContentHandler {
85
86 /**
87 * Given a URL connect stream positioned at the beginning of the
88 * representation of an object, this method reads that stream and
89 * creates an object from it.
90 *
91 * @param urlc a URL connection.
92 * @return the object read by the {@code ContentHandler}.
93 * @exception IOException if an I/O error occurs while reading the object.
94 */
95 abstract public Object getContent(URLConnection urlc) throws IOException;
96
97 /**
98 * Given a URL connect stream positioned at the beginning of the
99 * representation of an object, this method reads that stream and
100 * creates an object that matches one of the types specified.
101 *
102 * The default implementation of this method should call getContent()
103 * and screen the return type for a match of the suggested types.
104 *
105 * @param urlc a URL connection.
106 * @param classes an array of types requested
107 * @return the object read by the {@code ContentHandler} that is
108 * the first match of the suggested types or
109 * {@code null} if none of the requested are supported.
110 * @exception IOException if an I/O error occurs while reading the object.
111 * @since 1.3
112 */
113 @SuppressWarnings("rawtypes")
114 public Object getContent(URLConnection urlc, Class[] classes) throws IOException {
115 Object obj = getContent(urlc);
116
117 for (Class<?> c : classes) {
118 if (c.isInstance(obj)) {
119 return obj;
120 }
121 }
122 return null;
123 }
124 }