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.Objects;
34 import java.util.Optional;
35 import java.util.stream.Stream;
36
37
38 /**
39 * Provides access to the content of a module.
40 *
41 * <p> A module reader is intended for cases where access to the resources in a
42 * module is required, regardless of whether the module has been loaded.
43 * A framework that scans a collection of packaged modules on the file system,
44 * for example, may use a module reader to access a specific resource in each
45 * module. A module reader is also intended to be used by {@code ClassLoader}
46 * implementations that load classes and resources from modules. </p>
47 *
48 * <p> A resource in a module is identified by an abstract name that is a
49 * '{@code /}'-separated path string. For example, module {@code java.base} may
50 * have a resource "{@code java/lang/Object.class}" that, by convention, is the
51 * class file for {@code java.lang.Object}. </p>
52 *
53 * <p> A {@code ModuleReader} is {@linkplain ModuleReference#open open} upon
54 * creation and is closed by invoking the {@link #close close} method. Failure
55 * to close a module reader may result in a resource leak. The {@code
56 * try-with-resources} statement provides a useful construct to ensure that
57 * module readers are closed. </p>
58 *
59 * <p> A {@code ModuleReader} implementation may require permissions to access
60 * resources in the module. Consequently the {@link #find find}, {@link #open
61 * open}, {@link #read read}, and {@link #list list} methods may throw {@code
62 * SecurityException} if access is denied by the security manager. </p>
63 *
64 * @implSpec Implementations of {@code ModuleReader} should take great care
65 * when translating an abstract resource name to the location of a resource in
66 * a packaged module or on the file system. Implementations are advised to
67 * treat resource names with elements such as '{@code .}, '{@code ..}',
68 * elements containing file separators, or empty elements as "not found". More
69 * generally, if the resource name is not in the stream of elements that the
70 * {@code list} method returns then the resource should be treated as "not
71 * found" to avoid inconsistencies.
72 *
73 * @see ModuleReference
74 * @since 9
75 * @spec JPMS
76 */
77
78 public interface ModuleReader extends Closeable {
79
80 /**
81 * Finds a resource, returning a URI to the resource in the module.
82 *
83 * @param name
84 * The name of the resource to open for reading
85 *
86 * @return A URI to the resource; an empty {@code Optional} if the resource
87 * is not found or a URI cannot be constructed to locate the
88 * resource
89 *
90 * @throws IOException
91 * If an I/O error occurs or the module reader is closed
92 * @throws SecurityException
93 * If denied by the security manager
94 *
95 * @see ClassLoader#getResource(String)
96 */
97 Optional<URI> find(String name) throws IOException;
98
99 /**
100 * Opens a resource, returning an input stream to read the resource in
101 * the module.
102 *
103 * <p> The behavior of the input stream when used after the module reader
104 * is closed is implementation specific and therefore not specified. </p>
105 *
106 * @implSpec The default implementation invokes the {@link #find(String)
107 * find} method to get a URI to the resource. If found, then it attempts
108 * to construct a {@link java.net.URL URL} and open a connection to the
109 * resource.
110 *
111 * @param name
112 * The name of the resource to open for reading
113 *
114 * @return An input stream to read the resource or an empty
115 * {@code Optional} if not found
116 *
117 * @throws IOException
118 * If an I/O error occurs or the module reader is closed
119 * @throws SecurityException
120 * If denied by the security manager
121 */
122 default Optional<InputStream> open(String name) throws IOException {
123 Optional<URI> ouri = find(name);
124 if (ouri.isPresent()) {
125 return Optional.of(ouri.get().toURL().openStream());
126 } else {
127 return Optional.empty();
128 }
129 }
130
131 /**
132 * Reads a resource, returning a byte buffer with the contents of the
133 * resource.
134 *
135 * The element at the returned buffer's position is the first byte of the
136 * resource, the element at the buffer's limit is the last byte of the
137 * resource. Once consumed, the {@link #release(ByteBuffer) release} method
138 * must be invoked. Failure to invoke the {@code release} method may result
139 * in a resource leak.
140 *
141 * @apiNote This method is intended for high-performance class loading. It
142 * is not capable (or intended) to read arbitrary large resources that
143 * could potentially be 2GB or larger. The rational for using this method
144 * in conjunction with the {@code release} method is to allow module reader
145 * implementations manage buffers in an efficient manner.
146 *
147 * @implSpec The default implementation invokes the {@link #open(String)
148 * open} method and reads all bytes from the input stream into a byte
149 * buffer.
150 *
151 * @param name
152 * The name of the resource to read
153 *
154 * @return A byte buffer containing the contents of the resource or an
155 * empty {@code Optional} if not found
156 *
157 * @throws IOException
158 * If an I/O error occurs or the module reader is closed
159 * @throws SecurityException
160 * If denied by the security manager
161 * @throws OutOfMemoryError
162 * If the resource is larger than {@code Integer.MAX_VALUE},
163 * the maximum capacity of a byte buffer
164 *
165 * @see ClassLoader#defineClass(String, ByteBuffer, java.security.ProtectionDomain)
166 */
167 default Optional<ByteBuffer> read(String name) throws IOException {
168 Optional<InputStream> oin = open(name);
169 if (oin.isPresent()) {
170 try (InputStream in = oin.get()) {
171 return Optional.of(ByteBuffer.wrap(in.readAllBytes()));
172 }
173 } else {
174 return Optional.empty();
175 }
176 }
177
178 /**
179 * Release a byte buffer. This method should be invoked after consuming
180 * the contents of the buffer returned by the {@code read} method.
181 * The behavior of this method when invoked to release a buffer that has
182 * already been released, or the behavior when invoked to release a buffer
183 * after a {@code ModuleReader} is closed is implementation specific and
184 * therefore not specified.
185 *
186 * @param bb
187 * The byte buffer to release
188 *
189 * @implSpec The default implementation doesn't do anything except check
190 * if the byte buffer is null.
191 */
192 default void release(ByteBuffer bb) {
193 Objects.requireNonNull(bb);
194 }
195
196 /**
197 * Lists the contents of the module, returning a stream of elements that
198 * are the names of all resources in the module.
199 *
200 * <p> In lazy implementations then an {@code IOException} may be thrown
201 * when using the stream to list the module contents. If this occurs then
202 * the {@code IOException} will be wrapped in an {@link
203 * java.io.UncheckedIOException} and thrown from the method that caused the
204 * access to be attempted. {@code SecurityException} may also be thrown
205 * when using the stream to list the module contents and access is denied
206 * by the security manager. </p>
207 *
208 * <p> The behavior of the stream when used after the module reader is
209 * closed is implementation specific and therefore not specified. </p>
210 *
211 * @return A stream of elements that are the names of all resources
212 * in the module
213 *
214 * @throws IOException
215 * If an I/O error occurs or the module reader is closed
216 * @throws SecurityException
217 * If denied by the security manager
218 */
219 Stream<String> list() throws IOException;
220
221 /**
222 * Closes the module reader. Once closed then subsequent calls to locate or
223 * read a resource will fail by throwing {@code IOException}.
224 *
225 * <p> A module reader is not required to be asynchronously closeable. If a
226 * thread is reading a resource and another thread invokes the close method,
227 * then the second thread may block until the read operation is complete. </p>
228 */
229 @Override
230 void close() throws IOException;
231
232 }