Module java.base
Package java.nio.channels

Class AsynchronousSocketChannel

  • All Implemented Interfaces:
    Closeable, AutoCloseable, AsynchronousByteChannel, AsynchronousChannel, Channel, NetworkChannel
    public abstract class AsynchronousSocketChannel
extends Object
implements AsynchronousByteChannel, NetworkChannel
    An asynchronous channel for stream-oriented connecting sockets.

    Asynchronous socket channels are created in one of two ways. A newly-created AsynchronousSocketChannel is created by invoking one of the open methods defined by this class. A newly-created channel is open but not yet connected. A connected AsynchronousSocketChannel is created when a connection is made to the socket of an AsynchronousServerSocketChannel. It is not possible to create an asynchronous socket channel for an arbitrary, pre-existing socket.

    A newly-created channel is connected by invoking its connect method; once connected, a channel remains connected until it is closed. Whether or not a socket channel is connected may be determined by invoking its getRemoteAddress method. An attempt to invoke an I/O operation upon an unconnected channel will cause a NotYetConnectedException to be thrown.

    Channels of this type are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one read operation and one write operation can be outstanding at any time. If a thread initiates a read operation before a previous read operation has completed then a ReadPendingException will be thrown. Similarly, an attempt to initiate a write operation before a previous write has completed will throw a WritePendingException.

    Socket options are configured using the setOption method. Asynchronous 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
    TCP_NODELAY Disable the Nagle algorithm
    Additional (implementation specific) options may also be supported.

    Timeouts

    The read and write methods defined by this class allow a timeout to be specified when initiating a read or write operation. If the timeout elapses before an operation completes then the operation completes with the exception InterruptedByTimeoutException. A timeout may leave the channel, or the underlying connection, in an inconsistent state. Where the implementation cannot guarantee that bytes have not been read from the channel then it puts the channel into an implementation specific error state. A subsequent attempt to initiate a read operation causes an unspecified runtime exception to be thrown. Similarly if a write operation times out and the implementation cannot guarantee bytes have not been written to the channel then further attempts to write to the channel cause an unspecified runtime exception to be thrown. When a timeout elapses then the state of the ByteBuffer, or the sequence of buffers, for the I/O operation is not defined. Buffers should be discarded or at least care must be taken to ensure that the buffers are not accessed while the channel remains open. All methods that accept timeout parameters treat values less than or equal to zero to mean that the I/O operation does not timeout.

    Since:
    1.7

    • Constructor Detail

      • AsynchronousSocketChannel

        protected AsynchronousSocketChannel​(AsynchronousChannelProvider provider)
        Initializes a new instance of this class.
        Parameters:
        provider - The provider that created this channel

    • Method Detail

      • provider

        public final AsynchronousChannelProvider provider()
        Returns the provider that created this channel.
        Returns:
        The provider that created this channel

      • open

        public static AsynchronousSocketChannel open()
                                      throws IOException
        Opens an asynchronous socket channel.

        This method returns an asynchronous socket channel that is bound to the default group.This method is equivalent to evaluating the expression: 

         open((AsynchronousChannelGroup)null);
        Returns:
        A new asynchronous socket channel
        Throws:
        IOException - If an I/O error occurs

      • shutdownInput

        public abstract AsynchronousSocketChannel shutdownInput()
                                                 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. The effect on an outstanding read operation is system dependent and therefore not specified. The effect, if any, when there is data in the socket receive buffer that has not been read, or data arrives subsequently, is also system dependent.

        Returns:
        The channel
        Throws:
        NotYetConnectedException - If this channel is not yet connected
        ClosedChannelException - If this channel is closed
        IOException - If some other I/O error occurs

      • shutdownOutput

        public abstract AsynchronousSocketChannel shutdownOutput()
                                                  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. The effect on an outstanding write operation is system dependent and therefore not specified.

        Returns:
        The channel
        Throws:
        NotYetConnectedException - If this channel is not yet connected
        ClosedChannelException - If this channel is closed
        IOException - If some other I/O error occurs

      • getRemoteAddress

        public abstract SocketAddress getRemoteAddress()
                                        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.

        Returns:
        The remote address; null if the channel's socket is not connected
        Throws:
        ClosedChannelException - If the channel is closed
        IOException - If an I/O error occurs

      • connect

        public abstract <A> void connect​(SocketAddress remote,
                                 A attachment,
                                 CompletionHandler<Void,? super A> handler)
        Connects this channel.

        This method initiates an operation to connect this channel. The handler parameter is a completion handler that is invoked when the connection is successfully established or connection cannot be established. If the connection cannot be established then the channel is closed.

        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.

        Type Parameters:
        A - The type of the attachment
        Parameters:
        remote - The remote address to which this channel is to be connected
        attachment - The object to attach to the I/O operation; can be null
        handler - The handler for consuming the result
        Throws:
        UnresolvedAddressException - If the given remote address is not fully resolved
        UnsupportedAddressTypeException - If the type of the given remote address is not supported
        AlreadyConnectedException - If this channel is already connected
        ConnectionPendingException - If a connection operation is already in progress on this channel
        ShutdownChannelGroupException - If the channel group has terminated
        SecurityException - If a security manager has been installed and it does not permit access to the given remote endpoint
        See Also:
        getRemoteAddress()

      • connect

        public abstract Future<Void> connect​(SocketAddress remote)
        Connects this channel.

        This method initiates an operation to connect this channel. This method behaves in exactly the same manner as the connect(SocketAddress, Object, CompletionHandler) method except that instead of specifying a completion handler, this method returns a Future representing the pending result. The Future's get method returns null on successful completion.

        Parameters:
        remote - The remote address to which this channel is to be connected
        Returns:
        A Future object representing the pending result
        Throws:
        UnresolvedAddressException - If the given remote address is not fully resolved
        UnsupportedAddressTypeException - If the type of the given remote address is not supported
        AlreadyConnectedException - If this channel is already connected
        ConnectionPendingException - If a connection operation is already in progress on this channel
        SecurityException - If a security manager has been installed and it does not permit access to the given remote endpoint

      • read

        public abstract <A> void read​(ByteBuffer dst,
                              long timeout,
                              TimeUnit unit,
                              A attachment,
                              CompletionHandler<Integer,? super A> handler)
        Reads a sequence of bytes from this channel into the given buffer.

        This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The handler parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or -1 if no bytes could be read because the channel has reached end-of-stream.

        If a timeout is specified and the timeout elapses before the operation completes then the operation completes with the exception InterruptedByTimeoutException. Where a timeout occurs, and the implementation cannot guarantee that bytes have not been read, or will not be read from the channel into the given buffer, then further attempts to read from the channel will cause an unspecific runtime exception to be thrown.

        Otherwise this method works in the same manner as the AsynchronousByteChannel.read(ByteBuffer,Object,CompletionHandler) method.

        Type Parameters:
        A - The type of the attachment
        Parameters:
        dst - The buffer into which bytes are to be transferred
        timeout - The maximum time for the I/O operation to complete
        unit - The time unit of the timeout argument
        attachment - The object to attach to the I/O operation; can be null
        handler - The handler for consuming the result
        Throws:
        IllegalArgumentException - If the buffer is read-only
        ReadPendingException - If a read operation is already in progress on this channel
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • read

        public final <A> void read​(ByteBuffer dst,
                           A attachment,
                           CompletionHandler<Integer,? super A> handler)
        Description copied from interface: AsynchronousByteChannel
        Reads a sequence of bytes from this channel into the given buffer.

        This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The handler parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or -1 if no bytes could be read because the channel has reached end-of-stream.

        The read operation may read up to r bytes from the channel, where r is the number of bytes remaining in the buffer, that is, dst.remaining() at the time that the read is attempted. Where r is 0, the read operation completes immediately with a result of 0 without initiating an I/O operation.

        Suppose that a byte sequence of length n is read, where 0 < n <= r. This byte sequence will be transferred into the buffer so that the first byte in the sequence is at index p and the last byte is at index p + n - 1, where p is the buffer's position at the moment the read is performed. Upon completion the buffer's position will be equal to p + n; its limit will not have changed.

        Buffers are not safe for use by multiple concurrent threads so care should be taken to not access the buffer until the operation has completed.

        This method may be invoked at any time. Some channel types may not allow more than one read to be outstanding at any given time. If a thread initiates a read operation before a previous read operation has completed then a ReadPendingException will be thrown.

        Specified by:
        read in interface AsynchronousByteChannel
        Type Parameters:
        A - The type of the attachment
        Parameters:
        dst - The buffer into which bytes are to be transferred
        attachment - The object to attach to the I/O operation; can be null
        handler - The completion handler
        Throws:
        IllegalArgumentException - If the buffer is read-only
        ReadPendingException - If the channel does not allow more than one read to be outstanding and a previous read has not completed
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • read

        public abstract Future<Integer> read​(ByteBuffer dst)
        Description copied from interface: AsynchronousByteChannel
        Reads a sequence of bytes from this channel into the given buffer.

        This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The method behaves in exactly the same manner as the read(ByteBuffer,Object,CompletionHandler) method except that instead of specifying a completion handler, this method returns a Future representing the pending result. The Future's get method returns the number of bytes read or -1 if no bytes could be read because the channel has reached end-of-stream.

        Specified by:
        read in interface AsynchronousByteChannel
        Parameters:
        dst - The buffer into which bytes are to be transferred
        Returns:
        A Future representing the result of the operation
        Throws:
        IllegalArgumentException - If the buffer is read-only
        ReadPendingException - If the channel does not allow more than one read to be outstanding and a previous read has not completed
        NotYetConnectedException - If this channel is not yet connected

      • read

        public abstract <A> void read​(ByteBuffer[] dsts,
                              int offset,
                              int length,
                              long timeout,
                              TimeUnit unit,
                              A attachment,
                              CompletionHandler<Long,? super A> handler)
        Reads a sequence of bytes from this channel into a subsequence of the given buffers. This operation, sometimes called a scattering read, is often useful when implementing network protocols that group data into segments consisting of one or more fixed-length headers followed by a variable-length body. The handler parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or -1 if no bytes could be read because the channel has reached end-of-stream.

        This method initiates a read of up to r bytes from this channel, where r is the total number of bytes remaining in the specified subsequence of the given buffer array, that is, 

         dsts[offset].remaining()
     + dsts[offset+1].remaining()
     + ... + dsts[offset+length-1].remaining()
        at the moment that the read is attempted.

        Suppose that a byte sequence of length n is read, where 0 < n <= r. Up to the first dsts[offset].remaining() bytes of this sequence are transferred into buffer dsts[offset], up to the next dsts[offset+1].remaining() bytes are transferred into buffer dsts[offset+1], and so forth, until the entire byte sequence is transferred into the given buffers. As many bytes as possible are transferred into each buffer, hence the final position of each updated buffer, except the last updated buffer, is guaranteed to be equal to that buffer's limit. The underlying operating system may impose a limit on the number of buffers that may be used in an I/O operation. Where the number of buffers (with bytes remaining), exceeds this limit, then the I/O operation is performed with the maximum number of buffers allowed by the operating system.

        If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception InterruptedByTimeoutException. Where a timeout occurs, and the implementation cannot guarantee that bytes have not been read, or will not be read from the channel into the given buffers, then further attempts to read from the channel will cause an unspecific runtime exception to be thrown.

        Type Parameters:
        A - The type of the attachment
        Parameters:
        dsts - The buffers into which bytes are to be transferred
        offset - The offset within the buffer array of the first buffer into which bytes are to be transferred; must be non-negative and no larger than dsts.length
        length - The maximum number of buffers to be accessed; must be non-negative and no larger than dsts.length - offset
        timeout - The maximum time for the I/O operation to complete
        unit - The time unit of the timeout argument
        attachment - The object to attach to the I/O operation; can be null
        handler - The handler for consuming the result
        Throws:
        IndexOutOfBoundsException - If the pre-conditions for the offset and length parameter aren't met
        IllegalArgumentException - If the buffer is read-only
        ReadPendingException - If a read operation is already in progress on this channel
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • write

        public abstract <A> void write​(ByteBuffer src,
                               long timeout,
                               TimeUnit unit,
                               A attachment,
                               CompletionHandler<Integer,? super A> handler)
        Writes a sequence of bytes to this channel from the given buffer.

        This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The handler parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written.

        If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception InterruptedByTimeoutException. Where a timeout occurs, and the implementation cannot guarantee that bytes have not been written, or will not be written to the channel from the given buffer, then further attempts to write to the channel will cause an unspecific runtime exception to be thrown.

        Otherwise this method works in the same manner as the AsynchronousByteChannel.write(ByteBuffer,Object,CompletionHandler) method.

        Type Parameters:
        A - The type of the attachment
        Parameters:
        src - The buffer from which bytes are to be retrieved
        timeout - The maximum time for the I/O operation to complete
        unit - The time unit of the timeout argument
        attachment - The object to attach to the I/O operation; can be null
        handler - The handler for consuming the result
        Throws:
        WritePendingException - If a write operation is already in progress on this channel
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • write

        public final <A> void write​(ByteBuffer src,
                            A attachment,
                            CompletionHandler<Integer,? super A> handler)
        Description copied from interface: AsynchronousByteChannel
        Writes a sequence of bytes to this channel from the given buffer.

        This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The handler parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written.

        The write operation may write up to r bytes to the channel, where r is the number of bytes remaining in the buffer, that is, src.remaining() at the time that the write is attempted. Where r is 0, the write operation completes immediately with a result of 0 without initiating an I/O operation.

        Suppose that a byte sequence of length n is written, where 0 < n <= r. This byte sequence will be transferred from the buffer starting at index p, where p is the buffer's position at the moment the write is performed; the index of the last byte written will be p + n - 1. Upon completion the buffer's position will be equal to p + n; its limit will not have changed.

        Buffers are not safe for use by multiple concurrent threads so care should be taken to not access the buffer until the operation has completed.

        This method may be invoked at any time. Some channel types may not allow more than one write to be outstanding at any given time. If a thread initiates a write operation before a previous write operation has completed then a WritePendingException will be thrown.

        Specified by:
        write in interface AsynchronousByteChannel
        Type Parameters:
        A - The type of the attachment
        Parameters:
        src - The buffer from which bytes are to be retrieved
        attachment - The object to attach to the I/O operation; can be null
        handler - The completion handler object
        Throws:
        WritePendingException - If the channel does not allow more than one write to be outstanding and a previous write has not completed
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • write

        public abstract Future<Integer> write​(ByteBuffer src)
        Description copied from interface: AsynchronousByteChannel
        Writes a sequence of bytes to this channel from the given buffer.

        This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The method behaves in exactly the same manner as the write(ByteBuffer,Object,CompletionHandler) method except that instead of specifying a completion handler, this method returns a Future representing the pending result. The Future's get method returns the number of bytes written.

        Specified by:
        write in interface AsynchronousByteChannel
        Parameters:
        src - The buffer from which bytes are to be retrieved
        Returns:
        A Future representing the result of the operation
        Throws:
        WritePendingException - If the channel does not allow more than one write to be outstanding and a previous write has not completed
        NotYetConnectedException - If this channel is not yet connected

      • write

        public abstract <A> void write​(ByteBuffer[] srcs,
                               int offset,
                               int length,
                               long timeout,
                               TimeUnit unit,
                               A attachment,
                               CompletionHandler<Long,? super A> handler)
        Writes a sequence of bytes to this channel from a subsequence of the given buffers. This operation, sometimes called a gathering write, is often useful when implementing network protocols that group data into segments consisting of one or more fixed-length headers followed by a variable-length body. The handler parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written.

        This method initiates a write of up to r bytes to this channel, where r is the total number of bytes remaining in the specified subsequence of the given buffer array, that is, 

         srcs[offset].remaining()
     + srcs[offset+1].remaining()
     + ... + srcs[offset+length-1].remaining()
        at the moment that the write is attempted.

        Suppose that a byte sequence of length n is written, where 0 < n <= r. Up to the first srcs[offset].remaining() bytes of this sequence are written from buffer srcs[offset], up to the next srcs[offset+1].remaining() bytes are written from buffer srcs[offset+1], and so forth, until the entire byte sequence is written. As many bytes as possible are written from each buffer, hence the final position of each updated buffer, except the last updated buffer, is guaranteed to be equal to that buffer's limit. The underlying operating system may impose a limit on the number of buffers that may be used in an I/O operation. Where the number of buffers (with bytes remaining), exceeds this limit, then the I/O operation is performed with the maximum number of buffers allowed by the operating system.

        If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception InterruptedByTimeoutException. Where a timeout occurs, and the implementation cannot guarantee that bytes have not been written, or will not be written to the channel from the given buffers, then further attempts to write to the channel will cause an unspecific runtime exception to be thrown.

        Type Parameters:
        A - The type of the attachment
        Parameters:
        srcs - The buffers from which bytes are to be retrieved
        offset - The offset within the buffer array of the first buffer from which bytes are to be retrieved; must be non-negative and no larger than srcs.length
        length - The maximum number of buffers to be accessed; must be non-negative and no larger than srcs.length - offset
        timeout - The maximum time for the I/O operation to complete
        unit - The time unit of the timeout argument
        attachment - The object to attach to the I/O operation; can be null
        handler - The handler for consuming the result
        Throws:
        IndexOutOfBoundsException - If the pre-conditions for the offset and length parameter aren't met
        WritePendingException - If a write operation is already in progress on this channel
        NotYetConnectedException - If this channel is not yet connected
        ShutdownChannelGroupException - If the channel group has terminated

      • getLocalAddress

        public abstract SocketAddress getLocalAddress()
                                       throws IOException
        Returns the socket address that this channel's socket is bound to.

        Where the channel is bound to an Internet Protocol socket address then the return value from this method is of type InetSocketAddress.

        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.

        Specified by:
        getLocalAddress in interface NetworkChannel
        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
        Throws:
        ClosedChannelException - If the channel is closed
        IOException - If an I/O error occurs