A socket channel is created by invoking one of the {@code open} methods of * this class. The no-arg {@link #open() open} method opens a socket channel * for an Internet protocol socket. The {@link #open(ProtocolFamily)} * method is used to open a 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 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 for Internet protocol sockets support * following options: *
** ** * *
** * * *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 for Unix domain sockets support: *
** ** * *
** * * *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_LINGER SO_LINGER} *Linger on close if data is present (when configured in blocking mode * only) *
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 {@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 for an Internet protocol socket. * *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 * * @see * java.net.preferIPv4Stack system property */ public static SocketChannel open() throws IOException { return SelectorProvider.provider().openSocketChannel(); } /** * Opens a socket channel. The {@code family} parameter specifies the * {@link ProtocolFamily protocol family} of the channel's socket. * *The new channel is created by invoking the {@link * java.nio.channels.spi.SelectorProvider#openSocketChannel(ProtocolFamily) * openSocketChannel(ProtocolFamily)} method of the system-wide default. * {@link java.nio.channels.spi.SelectorProvider} object.
* * @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 * java.net.preferIPv4Stack system property * * @since 15 */ public static SocketChannel open(ProtocolFamily family) throws IOException { return SelectorProvider.provider().openSocketChannel(requireNonNull(family)); } /** * Opens a socket channel and connects it to a remote address. * *If the remote address is an {@link InetSocketAddress} then this * 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. * *
If the remote address is a {@link UnixDomainSocketAddress} then this * works by invoking the {@link #open(ProtocolFamily)} method with {@link * StandardProtocolFamily#UNIX} as parameter, invoking the {@link * #connect(SocketAddress) connect} method upon the resulting socket channel, * passing it {@code remote}, 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 an InetSocketAddress that 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 * * @see * java.net.preferIPv4Stack system property */ public static SocketChannel open(SocketAddress remote) throws IOException { SocketChannel sc; if (remote instanceof InetSocketAddress) sc = open(); else if (remote instanceof UnixDomainSocketAddress) sc = open(StandardProtocolFamily.UNIX); else throw new UnsupportedAddressTypeException(); 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 -- /** * Binds the channel's socket to a local address. * *
This method is used to establish an association between the socket
* and a local address. For Internet Protocol sockets, once an
* association is established then the socket remains bound until the
* channel is closed. If the {@code local} parameter has the value {@code
* null} then the socket will be bound to an address that is assigned
* automatically.
*
* @apiNote
* Binding a socket channel to a Unix Domain 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. If a socket channel to a Unix
* Domain socket is implicitly bound by connecting it without calling
* bind first, then its socket is
* unnamed
* with no corresponding socket file in the file-system. If a socket channel
* to a Unix Domain socket is automatically bound by calling {@code
* bind(null)} this results in an unnamed socket also.
*
* @implNote
* Each platform enforces an implementation specific maximum length for the
* name of a Unix Domain socket. This limitation is enforced when a
* channel is bound. The maximum length is typically close to and generally
* not less than 100 bytes.
*
* @param local The address to bind the socket, or {@code null} to bind
* the socket to an automatically assigned socket address
*
* @return This channel
*
* @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 for an Internet protocol socket address,
* or for a Unix domain socket address if it denies
* {@link NetPermission}{@code("accessUnixDomainSocket")}.
*
* @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.
*
* @return A socket associated with this channel
*
* @throws UnsupportedOperationException
* If the channel's socket is not an Internet protocol socket
*/
public abstract Socket socket();
/**
* 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.
*
* @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 {@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.
*
* For channels to Internet protocol sockets, 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.
*
* For channels to Unix Domain sockets, this method checks
* {@link java.net.NetPermission NetPermission}{@code
* ("accessUnixDomainSocket")} with the security manager's {@link
* SecurityManager#checkPermission(java.security.Permission)
* checkPermission} method.
*
* 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's socket is bound and connected to an Internet
* Protocol socket address then the return value is of type
* {@link java.net.InetSocketAddress}.
*
* Where the channel's socket is bound and connected to a Unix Domain
* socket address, the returned address is a {@link UnixDomainSocketAddress}.
*
* @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.
*
* Where the channel is bound to a Unix Domain 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;
}