Socket channels are not a complete abstraction of connecting network * sockets. Binding, shutdown, and the manipulation of socket options must be * done through an associated {@link java.net.Socket} object obtained by * invoking the {@link #socket() socket} method. It is not possible to create * a channel for an arbitrary, pre-existing socket, nor is it possible to * specify the {@link java.net.SocketImpl} object to be used by a socket * associated with a socket channel. * *
A socket channel is created by invoking one of the {@link #open open} * methods of this class. 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. * *
The input and output sides of a socket channel may independently be * shut down without actually closing the channel. Shutting down the * input side of a channel by invoking the {@link java.net.Socket#shutdownInput * shutdownInput} method of an associated socket object will cause further * reads on the channel to return -1, the end-of-stream indication. * Shutting down the output side of the channel by invoking the {@link * java.net.Socket#shutdownOutput shutdownOutput} method of an associated * socket object will cause further writes on the channel to throw a {@link * ClosedChannelException}. * *
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 -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 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 * @version 1.33, 03/12/19 * @since 1.4 */ public abstract class SocketChannel extends AbstractSelectableChannel implements ByteChannel, ScatteringByteChannel, GatheringByteChannel { /** * Initializes a new instance of this class. */ 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 remote, and then * returning that channel.
* * @param remote * The remote address to which the new channel is to be connected * * @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(); sc.connect(remote); return sc; } /** * Returns an operation set identifying this channel's supported * operations. * *Socket channels support connecting, reading, and writing, so this * method returns ({@link SelectionKey#OP_CONNECT} * | {@link SelectionKey#OP_READ} | {@link * SelectionKey#OP_WRITE}).
* * @return The valid-operation set */ public final int validOps() { return (SelectionKey.OP_READ | SelectionKey.OP_WRITE | SelectionKey.OP_CONNECT); } // -- Socket-specific operations -- /** * 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.
* * @return A socket associated with this channel */ public abstract Socket socket(); /** * Tells whether or not this channel's network socket is connected. * * @return true if, and only if, this channel's network socket * is connected */ public abstract boolean isConnected(); /** * Tells whether or not a connection operation is in progress on this * channel. * * @return 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 {@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.
* * @param remote * The remote address to which this channel is to be connected * * @return true if a connection was established, * 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 {@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 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.
* * @return 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; // -- 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); } }