https://openjdk.java.net/ 
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 * Copyright (c) 2000, 2017, 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,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.nio.channels;

import java.io.IOException;
import java.net.Socket;
import java.net.SocketOption;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.SelectorProvider;


A selectable channel for stream-oriented connecting sockets.

 A socket channel is created by invoking one of the open methods of this class. It is not possible to create a channel for an arbitrary, pre-existing socket. A newly-created socket channel is open but not yet connected. An attempt to invoke an I/O operation upon an unconnected channel will cause a NotYetConnectedException to be thrown. A socket channel can be connected by invoking its connect method; once connected, a socket channel remains connected until it is closed. Whether or not a socket channel is connected may be determined by invoking its isConnected method. 
 Socket channels support non-blocking connection: A socket channel may be created and the process of establishing the link to the remote socket may be initiated via the connect method for later completion by the finishConnect method. Whether or not a connection operation is in progress may be determined by invoking the isConnectionPending method. 
 Socket channels support asynchronous shutdown, which is similar to the asynchronous close operation specified in the Channel class. If the input side of a socket is shut down by one thread while another thread is blocked in a read operation on the socket's channel, then the read operation in the blocked thread will complete without reading any bytes and will return -1. If the output side of a socket is shut down by one thread while another thread is blocked in a write operation on the socket's channel, then the blocked thread will receive an AsynchronousCloseException. 
 Socket options are configured using the 
setOption method. Socket channels support the following options: 



Socket options

  

    Option Name
    Description
  



  

     SO_SNDBUF 
     The size of the socket send buffer 
  

  

     SO_RCVBUF 
     The size of the socket receive buffer 
  

  

     SO_KEEPALIVE 
     Keep connection alive 
  

  

     SO_REUSEADDR 
     Re-use address 
  

  

     SO_LINGER 
     Linger on close if data is present (when configured in blocking mode
         only) 
  

  

     TCP_NODELAY 
     Disable the Nagle algorithm 
  






Additional (implementation specific) options may also be supported.

 Socket channels are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one thread may be reading and at most one thread may be writing at any given time. The connect and finishConnect methods are mutually synchronized against each other, and an attempt to initiate a read or write operation while an invocation of one of these methods is in progress will block until that invocation is complete. 


Author:Mark Reinhold, JSR-51 Expert Group
Since:1.4
/**
 * A selectable channel for stream-oriented connecting sockets.
 *
 * <p> A socket channel is created by invoking one of the {@link #open open}
 * methods of this class.  It is not possible to create a channel for an arbitrary,
 * pre-existing socket. A newly-created socket channel is open but not yet
 * connected.  An attempt to invoke an I/O operation upon an unconnected
 * channel will cause a {@link NotYetConnectedException} to be thrown.  A
 * socket channel can be connected by invoking its {@link #connect connect}
 * method; once connected, a socket channel remains connected until it is
 * closed.  Whether or not a socket channel is connected may be determined by
 * invoking its {@link #isConnected isConnected} method.
 *
 * <p> Socket channels support <i>non-blocking connection:</i>&nbsp;A socket
 * channel may be created and the process of establishing the link to the
 * remote socket may be initiated via the {@link #connect connect} method for
 * later completion by the {@link #finishConnect finishConnect} method.
 * Whether or not a connection operation is in progress may be determined by
 * invoking the {@link #isConnectionPending isConnectionPending} method.
 *
 * <p> Socket channels support <i>asynchronous shutdown,</i> which is similar
 * to the asynchronous close operation specified in the {@link Channel} class.
 * If the input side of a socket is shut down by one thread while another
 * thread is blocked in a read operation on the socket's channel, then the read
 * operation in the blocked thread will complete without reading any bytes and
 * will return {@code -1}.  If the output side of a socket is shut down by one
 * thread while another thread is blocked in a write operation on the socket's
 * channel, then the blocked thread will receive an {@link
 * AsynchronousCloseException}.
 *
 * <p> Socket options are configured using the {@link #setOption(SocketOption,Object)
 * setOption} method. Socket channels 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_SNDBUF SO_SNDBUF} </th>
 *     <td> The size of the socket send buffer </td>
 *   </tr>
 *   <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_KEEPALIVE SO_KEEPALIVE} </th>
 *     <td> Keep connection alive </td>
 *   </tr>
 *   <tr>
 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} </th>
 *     <td> Re-use address </td>
 *   </tr>
 *   <tr>
 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_LINGER SO_LINGER} </th>
 *     <td> Linger on close if data is present (when configured in blocking mode
 *          only) </td>
 *   </tr>
 *   <tr>
 *     <th scope="row"> {@link java.net.StandardSocketOptions#TCP_NODELAY TCP_NODELAY} </th>
 *     <td> Disable the Nagle algorithm </td>
 *   </tr>
 * </tbody>
 * </table>
 * </blockquote>
 * Additional (implementation specific) options may also be supported.
 *
 * <p> Socket channels are safe for use by multiple concurrent threads.  They
 * support concurrent reading and writing, though at most one thread may be
 * reading and at most one thread may be writing at any given time.  The {@link
 * #connect connect} and {@link #finishConnect finishConnect} methods are
 * mutually synchronized against each other, and an attempt to initiate a read
 * or write operation while an invocation of one of these methods is in
 * progress will block until that invocation is complete.  </p>
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public abstract class SocketChannel
    extends AbstractSelectableChannel
    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, NetworkChannel
{

    
Initializes a new instance of this class.

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

    
Opens a socket channel.

 The new channel is created by invoking the 
openSocketChannel method of the system-wide default SelectorProvider object. 


Throws:
Returns: A new socket channel
/**
     * Opens a socket channel.
     *
     * <p> The new channel is created by invoking the {@link
     * java.nio.channels.spi.SelectorProvider#openSocketChannel
     * openSocketChannel} method of the system-wide default {@link
     * java.nio.channels.spi.SelectorProvider} object.  </p>
     *
     * @return  A new socket channel
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public static SocketChannel open() throws IOException {
        return SelectorProvider.provider().openSocketChannel();
    }

    
Opens a socket channel and connects it to a remote address.

 This convenience method works as if by invoking the open() method, invoking the connect method upon the resulting socket channel, passing it remote, and then returning that channel. 


Params:
  • remote – 
        The remote address to which the new channel is to be connected
Throws:
Returns: A new, and connected, socket channel
/**
     * Opens a socket channel and connects it to a remote address.
     *
     * <p> This convenience method works as if by invoking the {@link #open()}
     * method, invoking the {@link #connect(SocketAddress) connect} method upon
     * the resulting socket channel, passing it {@code remote}, and then
     * returning that channel.  </p>
     *
     * @param  remote
     *         The remote address to which the new channel is to be connected
     *
     * @return  A new, and connected, socket channel
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the connect operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  UnresolvedAddressException
     *          If the given remote address is not fully resolved
     *
     * @throws  UnsupportedAddressTypeException
     *          If the type of the given remote address is not supported
     *
     * @throws  SecurityException
     *          If a security manager has been installed
     *          and it does not permit access to the given remote endpoint
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public static SocketChannel open(SocketAddress remote)
        throws IOException
    {
        SocketChannel sc = open();
        try {
            sc.connect(remote);
        } catch (Throwable x) {
            try {
                sc.close();
            } catch (Throwable suppressed) {
                x.addSuppressed(suppressed);
            }
            throw x;
        }
        assert sc.isConnected();
        return sc;
    }

    
Returns an operation set identifying this channel's supported
operations.

 Socket channels support connecting, reading, and writing, so this method returns (SelectionKey.OP_CONNECT | SelectionKey.OP_READ | SelectionKey.OP_WRITE). 
Returns: The valid-operation set
/**
     * Returns an operation set identifying this channel's supported
     * operations.
     *
     * <p> Socket channels support connecting, reading, and writing, so this
     * method returns {@code (}{@link SelectionKey#OP_CONNECT}
     * {@code |}&nbsp;{@link SelectionKey#OP_READ} {@code |}&nbsp;{@link
     * SelectionKey#OP_WRITE}{@code )}.
     *
     * @return  The valid-operation set
     */
    public final int validOps() {
        return (SelectionKey.OP_READ
                | SelectionKey.OP_WRITE
                | SelectionKey.OP_CONNECT);
    }


    // -- Socket-specific operations --

    
Throws:
Since:1.7
/**
     * @throws  ConnectionPendingException
     *          If a non-blocking connect operation is already in progress on
     *          this channel
     * @throws  AlreadyBoundException               {@inheritDoc}
     * @throws  UnsupportedAddressTypeException     {@inheritDoc}
     * @throws  ClosedChannelException              {@inheritDoc}
     * @throws  IOException                         {@inheritDoc}
     * @throws  SecurityException
     *          If a security manager has been installed and its
     *          {@link SecurityManager#checkListen checkListen} method denies
     *          the operation
     *
     * @since 1.7
     */
    @Override
    public abstract SocketChannel bind(SocketAddress local)
        throws IOException;

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

    
Shutdown the connection for reading without closing the channel.

 Once shutdown for reading then further reads on the channel will return -1, the end-of-stream indication. If the input side of the connection is already shutdown then invoking this method has no effect. 
Throws:
Returns: The channel
Since:1.7
/**
     * Shutdown the connection for reading without closing the channel.
     *
     * <p> Once shutdown for reading then further reads on the channel will
     * return {@code -1}, the end-of-stream indication. If the input side of the
     * connection is already shutdown then invoking this method has no effect.
     *
     * @return  The channel
     *
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException
     *          If this channel is closed
     * @throws  IOException
     *          If some other I/O error occurs
     *
     * @since 1.7
     */
    public abstract SocketChannel shutdownInput() throws IOException;

    
Shutdown the connection for writing without closing the channel.

 Once shutdown for writing then further attempts to write to the channel will throw ClosedChannelException. If the output side of the connection is already shutdown then invoking this method has no effect. 
Throws:
Returns: The channel
Since:1.7
/**
     * Shutdown the connection for writing without closing the channel.
     *
     * <p> Once shutdown for writing then further attempts to write to the
     * channel will throw {@link ClosedChannelException}. If the output side of
     * the connection is already shutdown then invoking this method has no
     * effect.
     *
     * @return  The channel
     *
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException
     *          If this channel is closed
     * @throws  IOException
     *          If some other I/O error occurs
     *
     * @since 1.7
     */
    public abstract SocketChannel shutdownOutput() throws IOException;

    
Retrieves a socket associated with this channel.

 The returned object will not declare any public methods that are not declared in the Socket class. 


Returns: A socket associated with this channel
/**
     * Retrieves a socket associated with this channel.
     *
     * <p> The returned object will not declare any public methods that are not
     * declared in the {@link java.net.Socket} class.  </p>
     *
     * @return  A socket associated with this channel
     */
    public abstract Socket socket();

    
Tells whether or not this channel's network socket is connected.

Returns: true if, and only if, this channel's network socket is open and connected
/**
     * Tells whether or not this channel's network socket is connected.
     *
     * @return  {@code true} if, and only if, this channel's network socket
     *          is {@link #isOpen open} and connected
     */
    public abstract boolean isConnected();

    
Tells whether or not a connection operation is in progress on this
channel.

Returns: true if, and only if, a connection operation has been initiated on this channel but not yet completed by invoking the finishConnect method
/**
     * Tells whether or not a connection operation is in progress on this
     * channel.
     *
     * @return  {@code true} if, and only if, a connection operation has been
     *          initiated on this channel but not yet completed by invoking the
     *          {@link #finishConnect finishConnect} method
     */
    public abstract boolean isConnectionPending();

    
Connects this channel's socket.

 If this channel is in non-blocking mode then an invocation of this method initiates a non-blocking connection operation. If the connection is established immediately, as can happen with a local connection, then this method returns true. Otherwise this method returns false and the connection operation must later be completed by invoking the finishConnect method. 
 If this channel is in blocking mode then an invocation of this
method will block until the connection is established or an I/O error
occurs.

 This method performs exactly the same security checks as the Socket class. That is, if a security manager has been installed then this method verifies that its checkConnect method permits connecting to the address and port number of the given remote endpoint. 
 This method may be invoked at any time.  If a read or write
operation upon this channel is invoked while an invocation of this
method is in progress then that operation will first block until this
invocation is complete.  If a connection attempt is initiated but fails,
that is, if an invocation of this method throws a checked exception,
then the channel will be closed.  


Params:
  • remote – 
        The remote address to which this channel is to be connected
Throws:
Returns: true if a connection was established, false if this channel is in non-blocking mode and the connection operation is in progress
/**
     * Connects this channel's socket.
     *
     * <p> If this channel is in non-blocking mode then an invocation of this
     * method initiates a non-blocking connection operation.  If the connection
     * is established immediately, as can happen with a local connection, then
     * this method returns {@code true}.  Otherwise this method returns
     * {@code false} and the connection operation must later be completed by
     * invoking the {@link #finishConnect finishConnect} method.
     *
     * <p> If this channel is in blocking mode then an invocation of this
     * method will block until the connection is established or an I/O error
     * occurs.
     *
     * <p> This method performs exactly the same security checks as the {@link
     * java.net.Socket} class.  That is, if a security manager has been
     * installed then this method verifies that its {@link
     * java.lang.SecurityManager#checkConnect checkConnect} method permits
     * connecting to the address and port number of the given remote endpoint.
     *
     * <p> This method may be invoked at any time.  If a read or write
     * operation upon this channel is invoked while an invocation of this
     * method is in progress then that operation will first block until this
     * invocation is complete.  If a connection attempt is initiated but fails,
     * that is, if an invocation of this method throws a checked exception,
     * then the channel will be closed.  </p>
     *
     * @param  remote
     *         The remote address to which this channel is to be connected
     *
     * @return  {@code true} if a connection was established,
     *          {@code false} if this channel is in non-blocking mode
     *          and the connection operation is in progress
     *
     * @throws  AlreadyConnectedException
     *          If this channel is already connected
     *
     * @throws  ConnectionPendingException
     *          If a non-blocking connection operation is already in progress
     *          on this channel
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the connect operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  UnresolvedAddressException
     *          If the given remote address is not fully resolved
     *
     * @throws  UnsupportedAddressTypeException
     *          If the type of the given remote address is not supported
     *
     * @throws  SecurityException
     *          If a security manager has been installed
     *          and it does not permit access to the given remote endpoint
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract boolean connect(SocketAddress remote) throws IOException;

    
Finishes the process of connecting a socket channel.

 A non-blocking connection operation is initiated by placing a socket channel in non-blocking mode and then invoking its 
connect method. Once the connection is established, or the attempt has failed, the socket channel will become connectable and this method may be invoked to complete the connection sequence. If the connection operation failed then invoking this method will cause an appropriate IOException to be thrown. 
 If this channel is already connected then this method will not block and will immediately return true. If this channel is in non-blocking mode then this method will return false if the connection process is not yet complete. If this channel is in blocking mode then this method will block until the connection either completes or fails, and will always either return true or throw a checked exception describing the failure. 
 This method may be invoked at any time.  If a read or write
operation upon this channel is invoked while an invocation of this
method is in progress then that operation will first block until this
invocation is complete.  If a connection attempt fails, that is, if an
invocation of this method throws a checked exception, then the channel
will be closed.  


Throws:
Returns: true if, and only if, this channel's socket is now connected
/**
     * Finishes the process of connecting a socket channel.
     *
     * <p> A non-blocking connection operation is initiated by placing a socket
     * channel in non-blocking mode and then invoking its {@link #connect
     * connect} method.  Once the connection is established, or the attempt has
     * failed, the socket channel will become connectable and this method may
     * be invoked to complete the connection sequence.  If the connection
     * operation failed then invoking this method will cause an appropriate
     * {@link java.io.IOException} to be thrown.
     *
     * <p> If this channel is already connected then this method will not block
     * and will immediately return {@code true}.  If this channel is in
     * non-blocking mode then this method will return {@code false} if the
     * connection process is not yet complete.  If this channel is in blocking
     * mode then this method will block until the connection either completes
     * or fails, and will always either return {@code true} or throw a checked
     * exception describing the failure.
     *
     * <p> This method may be invoked at any time.  If a read or write
     * operation upon this channel is invoked while an invocation of this
     * method is in progress then that operation will first block until this
     * invocation is complete.  If a connection attempt fails, that is, if an
     * invocation of this method throws a checked exception, then the channel
     * will be closed.  </p>
     *
     * @return  {@code true} if, and only if, this channel's socket is now
     *          connected
     *
     * @throws  NoConnectionPendingException
     *          If this channel is not connected and a connection operation
     *          has not been initiated
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the connect operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract boolean finishConnect() throws IOException;

    
Returns the remote address to which this channel's socket is connected.

 Where the channel is bound and connected to an Internet Protocol socket address then the return value from this method is of type InetSocketAddress. 
Throws:
Returns: The remote address; null if the channel's socket is not connected
Since:1.7
/**
     * Returns the remote address to which this channel's socket is connected.
     *
     * <p> Where the channel is bound and connected to an Internet Protocol
     * socket address then the return value from this method is of type {@link
     * java.net.InetSocketAddress}.
     *
     * @return  The remote address; {@code null} if the channel's socket is not
     *          connected
     *
     * @throws  ClosedChannelException
     *          If the channel is closed
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @since 1.7
     */
    public abstract SocketAddress getRemoteAddress() throws IOException;

    // -- ByteChannel operations --

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public abstract int read(ByteBuffer dst) throws IOException;

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public abstract long read(ByteBuffer[] dsts, int offset, int length)
        throws IOException;

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public final long read(ByteBuffer[] dsts) throws IOException {
        return read(dsts, 0, dsts.length);
    }

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public abstract int write(ByteBuffer src) throws IOException;

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public abstract long write(ByteBuffer[] srcs, int offset, int length)
        throws IOException;

    
Throws:
  • NotYetConnectedException – 
         If this channel is not yet connected
/**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     */
    public final long write(ByteBuffer[] srcs) throws IOException {
        return write(srcs, 0, srcs.length);
    }

    
{@inheritDoc}

 If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, a SocketAddress representing the loopback address and the local port of the channel's socket is returned. 
Throws:
Returns: The SocketAddress that the socket is bound to, or the SocketAddress representing the loopback address if denied by the security manager, or null if the channel's socket is not bound
/**
     * {@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;

}