ContentHandler.java revision 12745:f068a4ffddd2 
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
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24 */
25
26package java.net;
27
28import 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 */
84public abstract 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    public abstract 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}
125