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* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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*/
package java.nio.channels.spi;
import java.io.
IOException;
import java.net.
ProtocolFamily;
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.
*
* @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
AccessController.
doPrivileged(
new
PrivilegedAction<
SelectorProvider>() {
public
SelectorProvider run() {
if (
loadProviderFromProperty())
return
provider;
if (
loadProviderAsService())
return
provider;
provider = sun.nio.ch.
DefaultSelectorProvider.
create();
return
provider;
}
});
}
}
/**
* Opens a datagram channel.
*
* @return The new channel
*
* @throws IOException
* If an I/O error occurs
*/
public abstract
DatagramChannel openDatagramChannel()
throws
IOException;
/**
* Opens a datagram channel.
*
* @param family
* The protocol family
*
* @return A new datagram channel
*
* @throws UnsupportedOperationException
* If the specified protocol family is not supported
* @throws IOException
* If an I/O error occurs
*
* @since 1.7
*/
public abstract
DatagramChannel openDatagramChannel(
ProtocolFamily family)
throws
IOException;
/**
* Opens a pipe.
*
* @return The new pipe
*
* @throws IOException
* If an I/O error occurs
*/
public abstract
Pipe openPipe()
throws
IOException;
/**
* Opens a selector.
*
* @return The new selector
*
* @throws IOException
* If an I/O error occurs
*/
public abstract
AbstractSelector openSelector()
throws
IOException;
/**
* Opens a server-socket channel.
*
* @return The new channel
*
* @throws IOException
* If an I/O error occurs
*/
public abstract
ServerSocketChannel openServerSocketChannel()
throws
IOException;
/**
* Opens a socket channel.
*
* @return The new channel
*
* @throws IOException
* If an I/O error occurs
*/
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;
}
}