1 /*
2 * Copyright (c) 2015, 2016, 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.lang.module;
27
28 import java.io.Closeable;
29 import java.io.IOException;
30 import java.io.InputStream;
31 import java.net.URI;
32 import java.nio.ByteBuffer;
33 import java.util.Optional;
34
35
36 /**
37 * Provides access to the content of a module.
38 *
39 * <p> A module reader is intended for cases where access to the resources in a
40 * module is required, regardless of whether the module has been loaded.
41 * A framework that scans a collection of packaged modules on the file system,
42 * for example, may use a module reader to access a specific resource in each
43 * module. A module reader is also intended to be used by {@code ClassLoader}
44 * implementations that load classes and resources from modules. </p>
45 *
46 * <p> A {@code ModuleReader} is {@linkplain ModuleReference#open open} upon
47 * creation and is closed by invoking the {@link #close close} method. Failure
48 * to close a module reader may result in a resource leak. The {@code
49 * try-with-resources} statement provides a useful construct to ensure that
50 * module readers are closed. </p>
51 *
52 * <p> A {@code ModuleReader} implementation may require permissions to access
53 * resources in the module. Consequently the {@link #find find}, {@link #open
54 * open} and {@link #read read} methods may throw {@code SecurityException} if
55 * access is denied by the security manager. </p>
56 *
57 * @see ModuleReference
58 * @since 9
59 */
60
61 public interface ModuleReader extends Closeable {
62
63 /**
64 * Finds a resource, returning a URI to the resource in the module.
65 *
66 * @param name
67 * The name of the resource to open for reading
68 *
69 * @return A URI to the resource; an empty {@code Optional} if the resource
70 * is not found or a URI cannot be constructed to locate the
71 * resource
72 *
73 * @throws IOException
74 * If an I/O error occurs or the module reader is closed
75 * @throws SecurityException
76 * If denied by the security manager
77 *
78 * @see ClassLoader#getResource(String)
79 */
80 Optional<URI> find(String name) throws IOException;
81
82 /**
83 * Opens a resource, returning an input stream to read the resource in
84 * the module.
85 *
86 * @implSpec The default implementation invokes the {@link #find(String)
87 * find} method to get a URI to the resource. If found, then it attempts
88 * to construct a {@link java.net.URL URL} and open a connection to the
89 * resource.
90 *
91 * @param name
92 * The name of the resource to open for reading
93 *
94 * @return An input stream to read the resource or an empty
95 * {@code Optional} if not found
96 *
97 * @throws IOException
98 * If an I/O error occurs or the module reader is closed
99 * @throws SecurityException
100 * If denied by the security manager
101 */
102 default Optional<InputStream> open(String name) throws IOException {
103 Optional<URI> ouri = find(name);
104 if (ouri.isPresent()) {
105 return Optional.of(ouri.getWhenPresent().toURL().openStream());
106 } else {
107 return Optional.empty();
108 }
109 }
110
111 /**
112 * Reads a resource, returning a byte buffer with the contents of the
113 * resource.
114 *
115 * The element at the returned buffer's position is the first byte of the
116 * resource, the element at the buffer's limit is the last byte of the
117 * resource. Once consumed, the {@link #release(ByteBuffer) release} method
118 * must be invoked. Failure to invoke the {@code release} method may result
119 * in a resource leak.
120 *
121 * @apiNote This method is intended for high-performance class loading. It
122 * is not capable (or intended) to read arbitrary large resources that
123 * could potentially be 2GB or larger. The rational for using this method
124 * in conjunction with the {@code release} method is to allow module reader
125 * implementations manage buffers in an efficient manner.
126 *
127 * @implSpec The default implementation invokes the {@link #open(String)
128 * open} method and reads all bytes from the input stream into a byte
129 * buffer.
130 *
131 * @param name
132 * The name of the resource to read
133 *
134 * @return A byte buffer containing the contents of the resource or an
135 * empty {@code Optional} if not found
136 *
137 * @throws IOException
138 * If an I/O error occurs or the module reader is closed
139 * @throws SecurityException
140 * If denied by the security manager
141 *
142 * @see ClassLoader#defineClass(String, ByteBuffer, java.security.ProtectionDomain)
143 */
144 default Optional<ByteBuffer> read(String name) throws IOException {
145 Optional<InputStream> in = open(name);
146 if (in.isPresent()) {
147 byte[] bytes = in.getWhenPresent().readAllBytes();
148 return Optional.of(ByteBuffer.wrap(bytes));
149 } else {
150 return Optional.empty();
151 }
152 }
153
154 /**
155 * Release a byte buffer. This method should be invoked after consuming
156 * the contents of the buffer returned by the {@code read} method.
157 * The behavior of this method when invoked to release a buffer that has
158 * already been released, or the behavior when invoked to release a buffer
159 * after a {@code ModuleReader} is closed is implementation specific and
160 * therefore not specified.
161 *
162 * @param bb
163 * The byte buffer to release
164 *
165 * @implSpec The default implementation does nothing.
166 */
167 default void release(ByteBuffer bb) { }
168
169 /**
170 * Closes the module reader. Once closed then subsequent calls to locate or
171 * read a resource will fail by returning {@code Optional.empty()} or
172 * throwing {@code IOException}.
173 *
174 * <p> A module reader is not required to be asynchronously closeable. If a
175 * thread is reading a resource and another thread invokes the close method,
176 * then the second thread may block until the read operation is complete.
177 *
178 * <p> The behavior of {@code InputStream}s obtained using the {@link
179 * #open(String) open} method and used after the module reader is closed
180 * is implementation specific and therefore not specified.
181 */
182 @Override
183 void close() throws IOException;
184
185 }