1 /*
2 * Copyright (c) 2000, 2017, 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 javax.print;
27
28 import java.io.IOException;
29
30 /**
31 * Interface {@code MultiDoc} specifies the interface for an object that
32 * supplies more than one piece of print data for a Print Job. "Doc" is a short,
33 * easy-to-pronounce term that means "a piece of print data," and a "multidoc"
34 * is a group of several docs. The client passes to the Print Job an object that
35 * implements interface {@code MultiDoc}, and the Print Job calls methods on
36 * that object to obtain the print data.
37 * <p>
38 * Interface {@code MultiDoc} provides an abstraction similar to a "linked list"
39 * of docs. A multidoc object is like a node in the linked list, containing the
40 * current doc in the list and a pointer to the next node (multidoc) in the
41 * list. The Print Job can call the multidoc's {@link #getDoc() getDoc()} method
42 * to get the current doc. When it's ready to go on to the next doc, the Print
43 * Job can call the multidoc's {@link #next() next()} method to get the next
44 * multidoc, which contains the next doc. So Print Job code for accessing a
45 * multidoc might look like this:
46 *
47 * <pre>
48 * void processMultiDoc(MultiDoc theMultiDoc) {
49 *
50 * MultiDoc current = theMultiDoc;
51 *
52 * while (current != null) {
53 * processDoc (current.getDoc());
54 * current = current.next();
55 * }
56 * }
57 * </pre>
58 * Of course, interface {@code MultiDoc} can be implemented in any way that
59 * fulfills the contract; it doesn't have to use a linked list in the
60 * implementation.
61 * <p>
62 * To get all the print data for a multidoc print job, a Print Service proxy
63 * could use either of two patterns:
64 * <ol type=1>
65 * <li>The <b>interleaved</b> pattern: Get the doc from the current multidoc.
66 * Get the print data representation object from the current doc. Get all the
67 * print data from the print data representation object. Get the next multidoc
68 * from the current multidoc, and repeat until there are no more. (The code
69 * example above uses the interleaved pattern.)
70 * <li>The <b>all-at-once</b> pattern: Get the doc from the current multidoc,
71 * and save the doc in a list. Get the next multidoc from the current
72 * multidoc, and repeat until there are no more. Then iterate over the list of
73 * saved docs. Get the print data representation object from the current doc.
74 * Get all the print data from the print data representation object. Go to the
75 * next doc in the list, and repeat until there are no more.
76 * </ol>
77 * Now, consider a printing client that is generating print data on the fly and
78 * does not have the resources to store more than one piece of print data at a
79 * time. If the print service proxy used the all-at-once pattern to get the
80 * print data, it would pose a problem for such a client; the client would have
81 * to keep all the docs' print data around until the print service proxy comes
82 * back and asks for them, which the client is not able to do. To work with such
83 * a client, the print service proxy must use the interleaved pattern.
84 * <p>
85 * To address this problem, and to simplify the design of clients providing
86 * multiple docs to a Print Job, every Print Service proxy that supports
87 * multidoc print jobs is required to access a {@code MultiDoc} object using the
88 * interleaved pattern. That is, given a {@code MultiDoc} object, the print
89 * service proxy will call {@link #getDoc() getDoc()} one or more times until it
90 * successfully obtains the current {@code Doc} object. The print service proxy
91 * will then obtain the current doc's print data, not proceeding until all the
92 * print data is obtained or an unrecoverable error occurs. If it is able to
93 * continue, the print service proxy will then call {@link #next() next()} one
94 * or more times until it successfully obtains either the next {@code MultiDoc}
95 * object or an indication that there are no more. An implementation of
96 * interface {@code MultiDoc} can assume the print service proxy will follow
97 * this interleaved pattern; for any other pattern of usage, the
98 * {@code MultiDoc} implementation's behavior is unspecified.
99 * <p>
100 * There is no restriction on the number of client threads that may be
101 * simultaneously accessing the same multidoc. Therefore, all implementations of
102 * interface MultiDoc must be designed to be multiple thread safe. In fact, a
103 * client thread could be adding docs to the end of the (conceptual) list while
104 * a Print Job thread is simultaneously obtaining docs from the beginning of the
105 * list; provided the multidoc object synchronizes the threads properly, the two
106 * threads will not interfere with each other.
107 */
108 public interface MultiDoc {
109
110 /**
111 * Obtain the current doc object.
112 *
113 * @return current doc object
114 * @throws IOException if an error occurred when reading the document
115 */
116 public Doc getDoc() throws IOException;
117
118 /**
119 * Go to the multidoc object that contains the next doc object in the
120 * sequence of doc objects.
121 *
122 * @return multidoc object containing the next doc object, or {@code null}
123 * if there are no further doc objects
124 * @throws IOException if an error occurred locating the next document
125 */
126 public MultiDoc next() throws IOException;
127 }