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	/*
	* Copyright (c) 2000, 2020, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.nio.channels;

	import java.io.IOException;
	import java.net.InetSocketAddress;
	import java.net.NetPermission;
	import java.net.ProtocolFamily;
	import java.net.ServerSocket;
	import java.net.SocketOption;
	import java.net.SocketAddress;
	import java.net.UnixDomainSocketAddress;
	import java.nio.channels.spi.AbstractSelectableChannel;
	import java.nio.channels.spi.SelectorProvider;
	import static java.util.Objects.requireNonNull;

	/**
	* A selectable channel for stream-oriented listening sockets.
	*
	* <p> A server-socket channel is created by invoking one of the {@code open}
	* methods of this class. The no-arg {@link #open() open} method opens a server-socket
	* channel for an <i>Internet protocol</i> socket. The {@link #open(ProtocolFamily)}
	* method is used to open a server-socket channel for a socket of a specified
	* protocol family. It is not possible to create a channel for an arbitrary,
	* pre-existing socket. A newly-created server-socket channel is open but not yet
	* bound. An attempt to invoke the {@link #accept() accept} method of an
	* unbound server-socket channel will cause a {@link NotYetBoundException}
	* to be thrown. A server-socket channel can be bound by invoking one of the
	* {@link #bind(java.net.SocketAddress, int) bind} methods defined by this class.
	*
	* <p> Socket options are configured using the {@link #setOption(SocketOption,Object)
	* setOption} method. Server-socket channels for <i>Internet protocol</i> sockets
	* support the following options:
	* <blockquote>
	* <table class="striped">
	* <caption style="display:none">Socket options</caption>
	* <thead>
	* <tr>
	* <th scope="col">Option Name</th>
	* <th scope="col">Description</th>
	* </tr>
	* </thead>
	* <tbody>
	* <tr>
	* <th scope="row"> {@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} </th>
	* <td> The size of the socket receive buffer </td>
	* </tr>
	* <tr>
	* <th scope="row"> {@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} </th>
	* <td> Re-use address </td>
	* </tr>
	* </tbody>
	* </table>
	* </blockquote>
	*
	* <p> Server-socket channels for <i>Unix domain</i> sockets support:
	* <blockquote>
	* <table class="striped">
	* <caption style="display:none">Socket options</caption>
	* <thead>
	* <tr>
	* <th scope="col">Option Name</th>
	* <th scope="col">Description</th>
	* </tr>
	* </thead>
	* <tbody>
	* <tr>
	* <th scope="row"> {@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} </th>
	* <td> The size of the socket receive buffer </td>
	* </tr>
	* </tbody>
	* </table>
	* </blockquote>
	*
	* <p> Additional (implementation specific) options may also be supported.
	*
	* <p> Server-socket channels are safe for use by multiple concurrent threads.
	* </p>
	*
	* @author Mark Reinhold
	* @author JSR-51 Expert Group
	* @since 1.4
	*/

	public abstract class ServerSocketChannel
	extends AbstractSelectableChannel
	implements NetworkChannel
	{

	/**
	* Initializes a new instance of this class.
	*
	* @param provider
	* The provider that created this channel
	*/
	protected ServerSocketChannel(SelectorProvider provider) {
	super(provider);
	}

	/**
	* Opens a server-socket channel for an <i>Internet protocol</i> socket.
	*
	* <p> The new channel is created by invoking the {@link
	* java.nio.channels.spi.SelectorProvider#openServerSocketChannel
	* openServerSocketChannel} method of the system-wide default {@link
	* java.nio.channels.spi.SelectorProvider} object.
	*
	* <p> The new channel's socket is initially unbound; it must be bound to a
	* specific address via one of its socket's {@link
	* java.net.ServerSocket#bind(SocketAddress) bind} methods before
	* connections can be accepted. </p>
	*
	* @return A new socket channel
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @see <a href="../../net/doc-files/net-properties.html#Ipv4IPv6">
	* java.net.preferIPv4Stack</a> system property
	*/
	public static ServerSocketChannel open() throws IOException {
	return SelectorProvider.provider().openServerSocketChannel();
	}

	/**
	* Opens a server-socket channel. The {@code family} parameter specifies the
	* {@link ProtocolFamily protocol family} of the channel's socket.
	*
	* <p> The new channel is created by invoking the {@link
	* java.nio.channels.spi.SelectorProvider#openServerSocketChannel(ProtocolFamily)
	* openServerSocketChannel(ProtocolFamily)} method of the system-wide default {@link
	* java.nio.channels.spi.SelectorProvider} object. </p>
	*
	* @param family
	* The protocol family
	*
	* @return A new socket channel
	*
	* @throws UnsupportedOperationException
	* If the specified protocol family is not supported. For example,
	* suppose the parameter is specified as {@link
	* java.net.StandardProtocolFamily#INET6 StandardProtocolFamily.INET6}
	* but IPv6 is not enabled on the platform.
	* @throws IOException
	* If an I/O error occurs
	*
	* @see <a href="../../net/doc-files/net-properties.html#Ipv4IPv6">
	* java.net.preferIPv4Stack</a> system property
	*
	* @since 15
	*/
	public static ServerSocketChannel open(ProtocolFamily family) throws IOException {
	return SelectorProvider.provider().openServerSocketChannel(requireNonNull(family));
	}

	/**
	* Returns an operation set identifying this channel's supported
	* operations.
	*
	* <p> Server-socket channels only support the accepting of new
	* connections, so this method returns {@link SelectionKey#OP_ACCEPT}.
	* </p>
	*
	* @return The valid-operation set
	*/
	public final int validOps() {
	return SelectionKey.OP_ACCEPT;
	}


	// -- ServerSocket-specific operations --

	/**
	* Binds the channel's socket to a local address and configures the socket
	* to listen for connections.
	*
	* <p> An invocation of this method is equivalent to the following:
	* <blockquote><pre>
	* bind(local, 0);
	* </pre></blockquote>
	*
	* @param local
	* The local address to bind the socket, or {@code null} to bind
	* to an automatically assigned socket address
	*
	* @return This channel
	*
	* @throws AlreadyBoundException {@inheritDoc}
	* @throws UnsupportedAddressTypeException {@inheritDoc}
	* @throws ClosedChannelException {@inheritDoc}
	* @throws IOException {@inheritDoc}
	* @throws SecurityException
	* If a security manager has been installed and it denies the
	* operation
	*
	* @since 1.7
	*/
	public final ServerSocketChannel bind(SocketAddress local)
	throws IOException
	{
	return bind(local, 0);
	}

	/**
	* Binds the channel's socket to a local address and configures the socket to
	* listen for connections.
	*
	* <p> This method is used to establish an association between the socket and
	* a local address. For <i>Internet protocol</i> sockets, once an association
	* is established then the socket remains bound until the channel is closed.
	*
	* <p> The {@code backlog} parameter is the maximum number of pending
	* connections on the socket. Its exact semantics are implementation specific.
	* In particular, an implementation may impose a maximum length or may choose
	* to ignore the parameter altogether. If the {@code backlog} parameter has
	* the value {@code 0}, or a negative value, then an implementation specific
	* default is used.
	*
	* @apiNote
	* Binding a server socket channel for a <i>Unix Domain</i> socket, creates a
	* file corresponding to the file path in the {@link UnixDomainSocketAddress}.
	* This file persists after the channel is closed, and must be removed before
	* another socket can bind to the same name. Binding to a {@code null} address
	* causes the socket to be <i>automatically</i> bound to some unique file
	* in a system temporary location. The associated socket file also persists
	* after the channel is closed. Its name can be obtained from the channel's
	* local socket address.
	*
	* @implNote
	* Each platform enforces an implementation specific, maximum length for the
	* name of a <i>Unix Domain</i> socket. This limitation is enforced when a
	* channel is bound. The maximum length is typically close to and generally
	* not less than 100 bytes. This limitation also applies to <i>automatically</i>
	* bound server socket channels. See the <i>Unix domain</i>
	* <a href="../../net/doc-files/net-properties.html#Unixdomain">networking
	* properties</a> that can be used to select the temporary directory where
	* these sockets are created.
	*
	* @param local
	* The address to bind the socket, or {@code null} to bind to
	* an automatically assigned socket address
	* @param backlog
	* The maximum number of pending connections
	*
	* @return This channel
	*
	* @throws AlreadyBoundException
	* If the socket is already bound
	* @throws UnsupportedAddressTypeException
	* If the type of the given address is not supported
	* @throws ClosedChannelException
	* If this channel is closed
	* @throws IOException
	* If some other I/O error occurs
	* @throws SecurityException
	* If a security manager has been installed and its {@link
	* SecurityManager#checkListen checkListen} method denies
	* the operation for an <i>Internet protocol</i> socket address,
	* or for a <i>Unix domain</i> socket address if it denies
	* {@link NetPermission}{@code("accessUnixDomainSocket")}.
	*
	* @since 1.7
	*/
	public abstract ServerSocketChannel bind(SocketAddress local, int backlog)
	throws IOException;

	/**
	* @throws UnsupportedOperationException {@inheritDoc}
	* @throws IllegalArgumentException {@inheritDoc}
	* @throws ClosedChannelException {@inheritDoc}
	* @throws IOException {@inheritDoc}
	*
	* @since 1.7
	*/
	public abstract <T> ServerSocketChannel setOption(SocketOption<T> name, T value)
	throws IOException;

	/**
	* Retrieves a server socket associated with this channel.
	*
	* <p> The returned object will not declare any public methods that are not
	* declared in the {@link java.net.ServerSocket} class. </p>
	*
	* @return A server socket associated with this channel
	*
	* @throws UnsupportedOperationException
	* If the channel's socket is not an <i>Internet protocol</i> socket
	*/
	public abstract ServerSocket socket();

	/**
	* Accepts a connection made to this channel's socket.
	*
	* <p> If this channel is in non-blocking mode then this method will
	* immediately return {@code null} if there are no pending connections.
	* Otherwise it will block indefinitely until a new connection is available
	* or an I/O error occurs.
	*
	* <p> The socket channel returned by this method, if any, will be in
	* blocking mode regardless of the blocking mode of this channel.
	*
	* <p> If bound to an <i>Internet protocol</i> socket address, this method
	* performs exactly the same security checks as the {@link
	* java.net.ServerSocket#accept accept} method of the {@link java.net.ServerSocket}
	* class. That is, if a security manager has been installed then for each
	* new connection this method verifies that the address and port number
	* of the connection's remote endpoint are permitted by the security
	* manager's {@link java.lang.SecurityManager#checkAccept checkAccept}
	* method. If bound to a <i>Unix Domain</i> socket address, this method checks
	* {@link NetPermission}{@code ("accessUnixDomainSocket")}.
	*
	* @return The socket channel for the new connection,
	* or {@code null} if this channel is in non-blocking mode
	* and no connection is available to be accepted
	*
	* @throws ClosedChannelException
	* If this channel is closed
	*
	* @throws AsynchronousCloseException
	* If another thread closes this channel
	* while the accept operation is in progress
	*
	* @throws ClosedByInterruptException
	* If another thread interrupts the current thread
	* while the accept operation is in progress, thereby
	* closing the channel and setting the current thread's
	* interrupt status
	*
	* @throws NotYetBoundException
	* If this channel's socket has not yet been bound
	*
	* @throws SecurityException
	* If a security manager has been installed and this
	* channel is bound to an {@link InetSocketAddress}
	* and the security manager denies access to the remote endpoint
	* of the new connection, or if this channel is bound to a
	* {@link UnixDomainSocketAddress} and the security manager
	* denies {@link NetPermission}{@code ("accessUnixDomainSocket")}
	*
	* @throws IOException
	* If some other I/O error occurs
	*/
	public abstract SocketChannel accept() throws IOException;

	/**
	* {@inheritDoc}
	*
	* If there is a security manager set, its {@code checkConnect} method is
	* called with the local address and {@code -1} as its arguments to see
	* if the operation is allowed. If the operation is not allowed,
	* a {@code SocketAddress} representing the
	* {@link java.net.InetAddress#getLoopbackAddress loopback} address and the
	* local port of the channel's socket is returned.
	*
	* <p> Where the channel is bound to a <i>Unix Domain</i> socket address, the socket
	* address is a {@link UnixDomainSocketAddress}. If there is a security manager
	* set, its {@link SecurityManager#checkPermission(java.security.Permission)
	* checkPermission} method is called with {@link NetPermission}{@code
	* ("accessUnixDomainSocket")}. If the operation is not allowed an unnamed
	* {@link UnixDomainSocketAddress} is returned.
	*
	* @return The {@code SocketAddress} that the socket is bound to, or the
	* {@code SocketAddress} representing the loopback address or empty
	* path if denied by the security manager, or {@code null} if the
	* channel's socket is not bound
	*
	* @throws ClosedChannelException {@inheritDoc}
	* @throws IOException {@inheritDoc}
	*/
	@Override
	public abstract SocketAddress getLocalAddress() throws IOException;
	}

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