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. * *
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 {@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. * *
Socket channels support asynchronous shutdown, 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}. * *
Socket options are configured using the {@link #setOption(SocketOption,Object) * setOption} method. Socket channels support the following options: *
** Additional (implementation specific) options may also be supported. * ** * *
** * * *Option Name *Description ** *{@link java.net.StandardSocketOptions#SO_SNDBUF SO_SNDBUF} *The size of the socket send buffer ** *{@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} *The size of the socket receive buffer ** *{@link java.net.StandardSocketOptions#SO_KEEPALIVE SO_KEEPALIVE} *Keep connection alive ** *{@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} *Re-use address ** *{@link java.net.StandardSocketOptions#SO_LINGER SO_LINGER} *Linger on close if data is present (when configured in blocking mode * only) ** * *{@link java.net.StandardSocketOptions#TCP_NODELAY TCP_NODELAY} *Disable the Nagle algorithm *
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.
* * @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. * * @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 {@link * java.nio.channels.spi.SelectorProvider#openSocketChannel * openSocketChannel} method of the system-wide default {@link * java.nio.channels.spi.SelectorProvider} object.
* * @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 {@link #open()} * method, invoking the {@link #connect(SocketAddress) connect} method upon * the resulting socket channel, passing it {@code remote}, and then * returning that channel.
* * @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 {@code (}{@link SelectionKey#OP_CONNECT}
* {@code |} {@link SelectionKey#OP_READ} {@code |} {@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 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 UnsupportedOperationException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws ClosedChannelException {@inheritDoc}
* @throws IOException {@inheritDoc}
*
* @since 1.7
*/
@Override
public abstract 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 {@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 {@link java.net.Socket} class. 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.
*
* 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 {@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.
*
* 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. 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.
*
* 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.
*
* 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. 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
*/
public abstract int read(ByteBuffer dst) throws IOException;
/**
* @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
*/
public final long read(ByteBuffer[] dsts) throws IOException {
return read(dsts, 0, dsts.length);
}
/**
* @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
*/
public abstract long write(ByteBuffer[] srcs, int offset, int length)
throws IOException;
/**
* @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 {@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;
}