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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * This code is free software; you can redistribute it and/or modify it

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 * 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.

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 * 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,

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 *

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package java.nio.channels;

import java.nio.channels.spi.*;

import java.net.SocketOption;

import java.net.SocketAddress;

import java.util.concurrent.Future;

import java.io.IOException;

/**

 * An asynchronous channel for stream-oriented listening sockets.

 *

 * <p> An asynchronous server-socket channel is created by invoking the

 * {@link #open open} method of this class.

 * A newly-created asynchronous server-socket channel is open but not yet bound.

 * It can be bound to a local address and configured to listen for connections

 * by invoking the {@link #bind(SocketAddress,int) bind} method. Once bound,

 * the {@link #accept(Object,CompletionHandler) accept} method

 * is used to initiate the accepting of connections to the channel's socket.

 * An attempt to invoke the {@code accept} method on an unbound channel will

 * cause a {@link NotYetBoundException} to be thrown.

 *

 * <p> Channels of this type are safe for use by multiple concurrent threads

 * though at most one accept operation can be outstanding at any time.

 * If a thread initiates an accept operation before a previous accept operation

 * has completed then an {@link AcceptPendingException} will be thrown.

 *

 * <p> Socket options are configured using the {@link #setOption(SocketOption,Object)

 * setOption} method. Channels of this type support the following options:

 * <blockquote>

 * <table class="striped">

 * <caption style="display:none">Socket options</caption>

 * <thead>

 *   <tr>

 *   </tr>

 * </thead>

 * <tbody>

 *   <tr>

 *     <td> The size of the socket receive buffer </td>

 *   </tr>

 *   <tr>

 *     <td> Re-use address </td>

 *   </tr>

 * </tbody>

 * </table>

 * </blockquote>

 * Additional (implementation specific) options may also be supported.

 *

 * <p> <b>Usage Example:</b>

 * <pre>

 *  final AsynchronousServerSocketChannel listener =

 *      AsynchronousServerSocketChannel.open().bind(new InetSocketAddress(5000));

 *

 *  listener.accept(null, new CompletionHandler<AsynchronousSocketChannel,Void>() {

 *      public void completed(AsynchronousSocketChannel ch, Void att) {

 *          // accept the next connection

 *          listener.accept(null, this);

 *

 *          // handle this connection

 *          handle(ch);

 *      }

 *      public void failed(Throwable exc, Void att) {

 *          ...

 *      }

 *  });

 * </pre>

 *

 * @since 1.7

 */

public abstract class AsynchronousServerSocketChannel

    implements AsynchronousChannel, NetworkChannel

{

    private final AsynchronousChannelProvider provider;

    /**

     * Initializes a new instance of this class.

     *

     * @param  provider

     *         The provider that created this channel

     */

    protected AsynchronousServerSocketChannel(AsynchronousChannelProvider provider) {

        this.provider = provider;

    }

    /**

     * Returns the provider that created this channel.

     *

     * @return  The provider that created this channel

     */

    public final AsynchronousChannelProvider provider() {

        return provider;

    }

    /**

     * Opens an asynchronous server-socket channel.

     *

     * <p> The new channel is created by invoking the {@link

     * java.nio.channels.spi.AsynchronousChannelProvider#openAsynchronousServerSocketChannel

     * openAsynchronousServerSocketChannel} method on the {@link

     * java.nio.channels.spi.AsynchronousChannelProvider} object that created

     * the given group. If the group parameter is {@code null} then the

     * resulting channel is created by the system-wide default provider, and

     * bound to the <em>default group</em>.

     *

     * @param   group

     *          The group to which the newly constructed channel should be bound,

     *          or {@code null} for the default group

     *

     * @return  A new asynchronous server socket channel

     *

     * @throws  ShutdownChannelGroupException

     *          If the channel group is shutdown

     * @throws  IOException

     *          If an I/O error occurs

     */

    public static AsynchronousServerSocketChannel open(AsynchronousChannelGroup group)

        throws IOException

    {

        AsynchronousChannelProvider provider = (group == null) ?

            AsynchronousChannelProvider.provider() : group.provider();

        return provider.openAsynchronousServerSocketChannel(group);

    }

    /**

     * Opens an asynchronous server-socket channel.

     *

     * <p> This method returns an asynchronous server socket channel that is

     * bound to the <em>default group</em>. This method is equivalent to evaluating

     * the expression:

     * <blockquote><pre>

     * open((AsynchronousChannelGroup)null);

     * </pre></blockquote>

     *

     * @return  A new asynchronous server socket channel

     *

     * @throws  IOException

     *          If an I/O error occurs

     */

    public static AsynchronousServerSocketChannel open()

        throws IOException

    {

        return open(null);

    }

    /**

     * 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  SecurityException                   {@inheritDoc}

     * @throws  ClosedChannelException              {@inheritDoc}

     * @throws  IOException                         {@inheritDoc}

     */

    public final AsynchronousServerSocketChannel 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. Once an association is established then the socket remains

     * bound until the associated 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 altogther. If the {@code backlog} parameter has

     * the value {@code 0}, or a negative value, then an implementation specific

     * default is used.

     *

     * @param   local

     *          The local 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  SecurityException

     *          If a security manager has been installed and its {@link

     *          SecurityManager#checkListen checkListen} method denies the operation

     * @throws  ClosedChannelException

     *          If the channel is closed

     * @throws  IOException

     *          If some other I/O error occurs

     */

    public abstract AsynchronousServerSocketChannel bind(SocketAddress local, int backlog)

        throws IOException;

    /**

     * @throws  IllegalArgumentException                {@inheritDoc}

     * @throws  ClosedChannelException                  {@inheritDoc}

     * @throws  IOException                             {@inheritDoc}

     */

    public abstract <T> AsynchronousServerSocketChannel setOption(SocketOption<T> name, T value)

        throws IOException;

    /**

     * Accepts a connection.

     *

     * <p> This method initiates an asynchronous operation to accept a

     * connection made to this channel's socket. The {@code handler} parameter is

     * a completion handler that is invoked when a connection is accepted (or

     * the operation fails). The result passed to the completion handler is

     * the {@link AsynchronousSocketChannel} to the new connection.

     *

     * <p> When a new connection is accepted then the resulting {@code

     * AsynchronousSocketChannel} will be bound to the same {@link

     * AsynchronousChannelGroup} as this channel. If the group is {@link

     * AsynchronousChannelGroup#isShutdown shutdown} and a connection is accepted,

     * then the connection is closed, and the operation completes with an {@code

     * IOException} and cause {@link ShutdownChannelGroupException}.

     *

     * <p> To allow for concurrent handling of new connections, the completion

     * handler is not invoked directly by the initiating thread when a new

     * connection is accepted immediately (see <a

     * href="AsynchronousChannelGroup.html#threading">Threading</a>).

     *

     * <p> If a security manager has been installed then it verifies that the

     * address and port number of the connection's remote endpoint are permitted

     * by the security manager's {@link SecurityManager#checkAccept checkAccept}

     * method. The permission check is performed with privileges that are restricted

     * by the calling context of this method. If the permission check fails then

     * the connection is closed and the operation completes with a {@link

     * SecurityException}.

     *

     * @param   <A>

     *          The type of the attachment

     * @param   attachment

     *          The object to attach to the I/O operation; can be {@code null}

     * @param   handler

     *          The handler for consuming the result

     *

     * @throws  AcceptPendingException

     *          If an accept operation is already in progress on this channel

     * @throws  NotYetBoundException

     *          If this channel's socket has not yet been bound

     * @throws  ShutdownChannelGroupException

     *          If the channel group has terminated

     */

    public abstract <A> void accept(A attachment,

                                    CompletionHandler<AsynchronousSocketChannel,? super A> handler);

    /**

     * Accepts a connection.

     *

     * <p> This method initiates an asynchronous operation to accept a

     * connection made to this channel's socket. The method behaves in exactly

     * the same manner as the {@link #accept(Object, CompletionHandler)} method

     * except that instead of specifying a completion handler, this method

     * returns a {@code Future} representing the pending result. The {@code

     * Future}'s {@link Future#get() get} method returns the {@link

     * AsynchronousSocketChannel} to the new connection on successful completion.

     *

     * @return  a {@code Future} object representing the pending result

     *

     * @throws  AcceptPendingException

     *          If an accept operation is already in progress on this channel

     * @throws  NotYetBoundException

     *          If this channel's socket has not yet been bound

     */

    public abstract Future<AsynchronousSocketChannel> accept();

    /**

     * {@inheritDoc}

     * <p>

     * 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.

     *

     * @return  The {@code SocketAddress} that the socket is bound to, or the

     *          {@code SocketAddress} representing the loopback address 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;

}