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* Copyright (c) 2000, 2006, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.nio.channels.spi;
import java.io.FileDescriptor;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.channels.*;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.ServiceLoader;
import java.util.ServiceConfigurationError;
import sun.security.action.GetPropertyAction;
/**
* Service-provider class for selectors and selectable channels.
*
* <p> A selector provider is a concrete subclass of this class that has a
* zero-argument constructor and implements the abstract methods specified
* below. A given invocation of the Java virtual machine maintains a single
* system-wide default provider instance, which is returned by the {@link
* #provider() provider} method. The first invocation of that method will locate
* the default provider as specified below.
*
* <p> The system-wide default provider is used by the static <tt>open</tt>
* methods of the {@link java.nio.channels.DatagramChannel#open
* DatagramChannel}, {@link java.nio.channels.Pipe#open Pipe}, {@link
* java.nio.channels.Selector#open Selector}, {@link
* java.nio.channels.ServerSocketChannel#open ServerSocketChannel}, and {@link
* java.nio.channels.SocketChannel#open SocketChannel} classes. It is also
* used by the {@link java.lang.System#inheritedChannel System.inheritedChannel()}
* method. A program may make use of a provider other than the default provider
* by instantiating that provider and then directly invoking the <tt>open</tt>
* methods defined in this class.
*
* <p> All of the methods in this class are safe for use by multiple concurrent
* threads. </p>
*
*
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class SelectorProvider {
private static final Object lock = new Object();
private static SelectorProvider provider = null;
/**
* Initializes a new instance of this class. </p>
*
* @throws SecurityException
* If a security manager has been installed and it denies
* {@link RuntimePermission}<tt>("selectorProvider")</tt>
*/
protected SelectorProvider() {
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkPermission(new RuntimePermission("selectorProvider"));
}
private static boolean loadProviderFromProperty() {
String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
if (cn == null)
return false;
try {
Class c = Class.forName(cn, true,
ClassLoader.getSystemClassLoader());
provider = (SelectorProvider)c.newInstance();
return true;
} catch (ClassNotFoundException x) {
throw new ServiceConfigurationError(null, x);
} catch (IllegalAccessException x) {
throw new ServiceConfigurationError(null, x);
} catch (InstantiationException x) {
throw new ServiceConfigurationError(null, x);
} catch (SecurityException x) {
throw new ServiceConfigurationError(null, x);
}
}
private static boolean loadProviderAsService() {
ServiceLoader<SelectorProvider> sl =
ServiceLoader.load(SelectorProvider.class,
ClassLoader.getSystemClassLoader());
Iterator<SelectorProvider> i = sl.iterator();
for (;;) {
try {
if (!i.hasNext())
return false;
provider = i.next();
return true;
} catch (ServiceConfigurationError sce) {
if (sce.getCause() instanceof SecurityException) {
// Ignore the security exception, try the next provider
continue;
}
throw sce;
}
}
}
/**
* Returns the system-wide default selector provider for this invocation of
* the Java virtual machine.
*
* <p> The first invocation of this method locates the default provider
* object as follows: </p>
*
* <ol>
*
* <li><p> If the system property
* <tt>java.nio.channels.spi.SelectorProvider</tt> is defined then it is
* taken to be the fully-qualified name of a concrete provider class.
* The class is loaded and instantiated; if this process fails then an
* unspecified error is thrown. </p></li>
*
* <li><p> If a provider class has been installed in a jar file that is
* visible to the system class loader, and that jar file contains a
* provider-configuration file named
* <tt>java.nio.channels.spi.SelectorProvider</tt> in the resource
* directory <tt>META-INF/services</tt>, then the first class name
* specified in that file is taken. The class is loaded and
* instantiated; if this process fails then an unspecified error is
* thrown. </p></li>
*
* <li><p> Finally, if no provider has been specified by any of the above
* means then the system-default provider class is instantiated and the
* result is returned. </p></li>
*
* </ol>
*
* <p> Subsequent invocations of this method return the provider that was
* returned by the first invocation. </p>
*
* @return The system-wide default selector provider
*/
public static SelectorProvider provider() {
synchronized (lock) {
if (provider != null)
return provider;
return (SelectorProvider)AccessController
.doPrivileged(new PrivilegedAction() {
public Object run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = sun.nio.ch.DefaultSelectorProvider.create();
return provider;
}
});
}
}
/**
* Opens a datagram channel. </p>
*
* @return The new channel
*/
public abstract DatagramChannel openDatagramChannel()
throws IOException;
/**
* Opens a pipe. </p>
*
* @return The new pipe
*/
public abstract Pipe openPipe()
throws IOException;
/**
* Opens a selector. </p>
*
* @return The new selector
*/
public abstract AbstractSelector openSelector()
throws IOException;
/**
* Opens a server-socket channel. </p>
*
* @return The new channel
*/
public abstract ServerSocketChannel openServerSocketChannel()
throws IOException;
/**
* Opens a socket channel. </p>
*
* @return The new channel
*/
public abstract SocketChannel openSocketChannel()
throws IOException;
/**
* Returns the channel inherited from the entity that created this
* Java virtual machine.
*
* <p> On many operating systems a process, such as a Java virtual
* machine, can be started in a manner that allows the process to
* inherit a channel from the entity that created the process. The
* manner in which this is done is system dependent, as are the
* possible entities to which the channel may be connected. For example,
* on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
* start programs to service requests when a request arrives on an
* associated network port. In this example, the process that is started,
* inherits a channel representing a network socket.
*
* <p> In cases where the inherited channel represents a network socket
* then the {@link java.nio.channels.Channel Channel} type returned
* by this method is determined as follows:
*
* <ul>
*
* <li><p> If the inherited channel represents a stream-oriented connected
* socket then a {@link java.nio.channels.SocketChannel SocketChannel} is
* returned. The socket channel is, at least initially, in blocking
* mode, bound to a socket address, and connected to a peer.
* </p></li>
*
* <li><p> If the inherited channel represents a stream-oriented listening
* socket then a {@link java.nio.channels.ServerSocketChannel
* ServerSocketChannel} is returned. The server-socket channel is, at
* least initially, in blocking mode, and bound to a socket address.
* </p></li>
*
* <li><p> If the inherited channel is a datagram-oriented socket
* then a {@link java.nio.channels.DatagramChannel DatagramChannel} is
* returned. The datagram channel is, at least initially, in blocking
* mode, and bound to a socket address.
* </p></li>
*
* </ul>
*
* <p> In addition to the network-oriented channels described, this method
* may return other kinds of channels in the future.
*
* <p> The first invocation of this method creates the channel that is
* returned. Subsequent invocations of this method return the same
* channel. </p>
*
* @return The inherited channel, if any, otherwise <tt>null</tt>.
*
* @throws IOException
* If an I/O error occurs
*
* @throws SecurityException
* If a security manager has been installed and it denies
* {@link RuntimePermission}<tt>("inheritedChannel")</tt>
*
* @since 1.5
*/
public Channel inheritedChannel() throws IOException {
return null;
}
}