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;
+
+}