1 /*
2 * Copyright (c) 2000, 2009, 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.nio.channels.spi;
27
28 import java.io.IOException;
29 import java.net.ProtocolFamily;
30 import java.nio.channels.*;
31 import java.security.AccessController;
32 import java.security.PrivilegedAction;
33 import java.util.Iterator;
34 import java.util.ServiceLoader;
35 import java.util.ServiceConfigurationError;
36 import sun.security.action.GetPropertyAction;
37
38
39 /**
40 * Service-provider class for selectors and selectable channels.
41 *
42 * <p> A selector provider is a concrete subclass of this class that has a
43 * zero-argument constructor and implements the abstract methods specified
44 * below. A given invocation of the Java virtual machine maintains a single
45 * system-wide default provider instance, which is returned by the {@link
46 * #provider() provider} method. The first invocation of that method will locate
47 * the default provider as specified below.
48 *
49 * <p> The system-wide default provider is used by the static <tt>open</tt>
50 * methods of the {@link java.nio.channels.DatagramChannel#open
51 * DatagramChannel}, {@link java.nio.channels.Pipe#open Pipe}, {@link
52 * java.nio.channels.Selector#open Selector}, {@link
53 * java.nio.channels.ServerSocketChannel#open ServerSocketChannel}, and {@link
54 * java.nio.channels.SocketChannel#open SocketChannel} classes. It is also
55 * used by the {@link java.lang.System#inheritedChannel System.inheritedChannel()}
56 * method. A program may make use of a provider other than the default provider
57 * by instantiating that provider and then directly invoking the <tt>open</tt>
58 * methods defined in this class.
59 *
60 * <p> All of the methods in this class are safe for use by multiple concurrent
61 * threads. </p>
62 *
63 *
64 * @author Mark Reinhold
65 * @author JSR-51 Expert Group
66 * @since 1.4
67 */
68
69 public abstract class SelectorProvider {
70
71 private static final Object lock = new Object();
72 private static SelectorProvider provider = null;
73
74 private static Void checkPermission() {
75 SecurityManager sm = System.getSecurityManager();
76 if (sm != null)
77 sm.checkPermission(new RuntimePermission("selectorProvider"));
78 return null;
79 }
80 private SelectorProvider(Void ignore) { }
81
82 /**
83 * Initializes a new instance of this class.
84 *
85 * @throws SecurityException
86 * If a security manager has been installed and it denies
87 * {@link RuntimePermission}<tt>("selectorProvider")</tt>
88 */
89 protected SelectorProvider() {
90 this(checkPermission());
91 }
92
93 private static boolean loadProviderFromProperty() {
94 String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
95 if (cn == null)
96 return false;
97 try {
98 Class<?> c = Class.forName(cn, true,
99 ClassLoader.getSystemClassLoader());
100 provider = (SelectorProvider)c.newInstance();
101 return true;
102 } catch (ClassNotFoundException x) {
103 throw new ServiceConfigurationError(null, x);
104 } catch (IllegalAccessException x) {
105 throw new ServiceConfigurationError(null, x);
106 } catch (InstantiationException x) {
107 throw new ServiceConfigurationError(null, x);
108 } catch (SecurityException x) {
109 throw new ServiceConfigurationError(null, x);
110 }
111 }
112
113 private static boolean loadProviderAsService() {
114
115 ServiceLoader<SelectorProvider> sl =
116 ServiceLoader.load(SelectorProvider.class,
117 ClassLoader.getSystemClassLoader());
118 Iterator<SelectorProvider> i = sl.iterator();
119 for (;;) {
120 try {
121 if (!i.hasNext())
122 return false;
123 provider = i.next();
124 return true;
125 } catch (ServiceConfigurationError sce) {
126 if (sce.getCause() instanceof SecurityException) {
127 // Ignore the security exception, try the next provider
128 continue;
129 }
130 throw sce;
131 }
132 }
133 }
134
135 /**
136 * Returns the system-wide default selector provider for this invocation of
137 * the Java virtual machine.
138 *
139 * <p> The first invocation of this method locates the default provider
140 * object as follows: </p>
141 *
142 * <ol>
143 *
144 * <li><p> If the system property
145 * <tt>java.nio.channels.spi.SelectorProvider</tt> is defined then it is
146 * taken to be the fully-qualified name of a concrete provider class.
147 * The class is loaded and instantiated; if this process fails then an
148 * unspecified error is thrown. </p></li>
149 *
150 * <li><p> If a provider class has been installed in a jar file that is
151 * visible to the system class loader, and that jar file contains a
152 * provider-configuration file named
153 * <tt>java.nio.channels.spi.SelectorProvider</tt> in the resource
154 * directory <tt>META-INF/services</tt>, then the first class name
155 * specified in that file is taken. The class is loaded and
156 * instantiated; if this process fails then an unspecified error is
157 * thrown. </p></li>
158 *
159 * <li><p> Finally, if no provider has been specified by any of the above
160 * means then the system-default provider class is instantiated and the
161 * result is returned. </p></li>
162 *
163 * </ol>
164 *
165 * <p> Subsequent invocations of this method return the provider that was
166 * returned by the first invocation. </p>
167 *
168 * @return The system-wide default selector provider
169 */
170 public static SelectorProvider provider() {
171 synchronized (lock) {
172 if (provider != null)
173 return provider;
174 return AccessController.doPrivileged(
175 new PrivilegedAction<SelectorProvider>() {
176 public SelectorProvider run() {
177 if (loadProviderFromProperty())
178 return provider;
179 if (loadProviderAsService())
180 return provider;
181 provider = sun.nio.ch.DefaultSelectorProvider.create();
182 return provider;
183 }
184 });
185 }
186 }
187
188 /**
189 * Opens a datagram channel.
190 *
191 * @return The new channel
192 *
193 * @throws IOException
194 * If an I/O error occurs
195 */
196 public abstract DatagramChannel openDatagramChannel()
197 throws IOException;
198
199 /**
200 * Opens a datagram channel.
201 *
202 * @param family
203 * The protocol family
204 *
205 * @return A new datagram channel
206 *
207 * @throws UnsupportedOperationException
208 * If the specified protocol family is not supported
209 * @throws IOException
210 * If an I/O error occurs
211 *
212 * @since 1.7
213 */
214 public abstract DatagramChannel openDatagramChannel(ProtocolFamily family)
215 throws IOException;
216
217 /**
218 * Opens a pipe.
219 *
220 * @return The new pipe
221 *
222 * @throws IOException
223 * If an I/O error occurs
224 */
225 public abstract Pipe openPipe()
226 throws IOException;
227
228 /**
229 * Opens a selector.
230 *
231 * @return The new selector
232 *
233 * @throws IOException
234 * If an I/O error occurs
235 */
236 public abstract AbstractSelector openSelector()
237 throws IOException;
238
239 /**
240 * Opens a server-socket channel.
241 *
242 * @return The new channel
243 *
244 * @throws IOException
245 * If an I/O error occurs
246 */
247 public abstract ServerSocketChannel openServerSocketChannel()
248 throws IOException;
249
250 /**
251 * Opens a socket channel.
252 *
253 * @return The new channel
254 *
255 * @throws IOException
256 * If an I/O error occurs
257 */
258 public abstract SocketChannel openSocketChannel()
259 throws IOException;
260
261 /**
262 * Returns the channel inherited from the entity that created this
263 * Java virtual machine.
264 *
265 * <p> On many operating systems a process, such as a Java virtual
266 * machine, can be started in a manner that allows the process to
267 * inherit a channel from the entity that created the process. The
268 * manner in which this is done is system dependent, as are the
269 * possible entities to which the channel may be connected. For example,
270 * on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
271 * start programs to service requests when a request arrives on an
272 * associated network port. In this example, the process that is started,
273 * inherits a channel representing a network socket.
274 *
275 * <p> In cases where the inherited channel represents a network socket
276 * then the {@link java.nio.channels.Channel Channel} type returned
277 * by this method is determined as follows:
278 *
279 * <ul>
280 *
281 * <li><p> If the inherited channel represents a stream-oriented connected
282 * socket then a {@link java.nio.channels.SocketChannel SocketChannel} is
283 * returned. The socket channel is, at least initially, in blocking
284 * mode, bound to a socket address, and connected to a peer.
285 * </p></li>
286 *
287 * <li><p> If the inherited channel represents a stream-oriented listening
288 * socket then a {@link java.nio.channels.ServerSocketChannel
289 * ServerSocketChannel} is returned. The server-socket channel is, at
290 * least initially, in blocking mode, and bound to a socket address.
291 * </p></li>
292 *
293 * <li><p> If the inherited channel is a datagram-oriented socket
294 * then a {@link java.nio.channels.DatagramChannel DatagramChannel} is
295 * returned. The datagram channel is, at least initially, in blocking
296 * mode, and bound to a socket address.
297 * </p></li>
298 *
299 * </ul>
300 *
301 * <p> In addition to the network-oriented channels described, this method
302 * may return other kinds of channels in the future.
303 *
304 * <p> The first invocation of this method creates the channel that is
305 * returned. Subsequent invocations of this method return the same
306 * channel. </p>
307 *
308 * @return The inherited channel, if any, otherwise <tt>null</tt>.
309 *
310 * @throws IOException
311 * If an I/O error occurs
312 *
313 * @throws SecurityException
314 * If a security manager has been installed and it denies
315 * {@link RuntimePermission}<tt>("inheritedChannel")</tt>
316 *
317 * @since 1.5
318 */
319 public Channel inheritedChannel() throws IOException {
320 return null;
321 }
322
323 }