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AsynchronousSocketChannel

public abstract class AsynchronousSocketChannel
extends Object implements AsynchronousByteChannel, NetworkChannel

java.lang.Object
   ↳ java.nio.channels.AsynchronousSocketChannel


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:

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.

Summary

Protected constructors

AsynchronousSocketChannel(AsynchronousChannelProvider provider)

Initializes a new instance of this class.

Public methods

abstract AsynchronousSocketChannel bind(SocketAddress local)

Binds the channel's socket to a local address.

abstract Future<Void> connect(SocketAddress remote)

Connects this channel.

abstract <A> void connect(SocketAddress remote, A attachment, CompletionHandler<Void, ? super A> handler)

Connects this channel.

abstract SocketAddress getLocalAddress()

Returns the socket address that this channel's socket is bound to.

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.

abstract SocketAddress getRemoteAddress()

Returns the remote address to which this channel's socket is connected.

static AsynchronousSocketChannel open(AsynchronousChannelGroup group)

Opens an asynchronous socket channel.

static AsynchronousSocketChannel open()

Opens an asynchronous socket channel.

final AsynchronousChannelProvider provider()

Returns the provider that created this channel.

abstract Future<Integer> read(ByteBuffer dst)

Reads a sequence of bytes from this channel into the given buffer.

final <A> void read(ByteBuffer dst, A attachment, CompletionHandler<Integer, ? super A> handler)

Reads a sequence of bytes from this channel into the given buffer.

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.

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.

abstract <T> AsynchronousSocketChannel setOption(SocketOption<T> name, T value)

Sets the value of a socket option.

abstract AsynchronousSocketChannel shutdownInput()

Shutdown the connection for reading without closing the channel.

abstract AsynchronousSocketChannel shutdownOutput()

Shutdown the connection for writing without closing the channel.

abstract Future<Integer> write(ByteBuffer src)

Writes a sequence of bytes to this channel from the given buffer.

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.

final <A> void write(ByteBuffer src, A attachment, CompletionHandler<Integer, ? super A> handler)

Writes a sequence of bytes to this channel from the given buffer.

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.

Inherited methods

Protected constructors

AsynchronousSocketChannel

added in API level 26
protected AsynchronousSocketChannel (AsynchronousChannelProvider provider)

Initializes a new instance of this class.

Parameters
provider AsynchronousChannelProvider: The provider that created this channel

Public methods

bind

added in API level 26
public abstract AsynchronousSocketChannel bind (SocketAddress local)

Binds the channel's socket to a local address.

This method is used to establish an association between the socket and a local address. Once an association is established then the socket remains bound until the channel is closed. If the local parameter has the value null then the socket will be bound to an address that is assigned automatically.

Parameters
local SocketAddress: The address to bind the socket, or null to bind the socket to an automatically assigned socket address

Returns
AsynchronousSocketChannel This channel

Throws
ConnectionPendingException If a connection operation is already in progress on this channel
AlreadyBoundException
UnsupportedAddressTypeException
ClosedChannelException
IOException
SecurityException If a security manager has been installed and its checkListen method denies the operation

connect

added in API level 26
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 SocketAddress: The remote address to which this channel is to be connected

Returns
Future<Void> 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

connect

added in API level 26
public abstract 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.

Parameters
remote SocketAddress: The remote address to which this channel is to be connected

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: 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:

getLocalAddress

added in API level 26
public abstract SocketAddress getLocalAddress ()

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.

Returns
SocketAddress 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
IOException

getRemoteAddress

added in API level 26
public abstract SocketAddress getRemoteAddress ()

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
SocketAddress 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

open

added in API level 26
public static AsynchronousSocketChannel open (AsynchronousChannelGroup group)

Opens an asynchronous socket channel.

The new channel is created by invoking the openAsynchronousSocketChannel method on the AsynchronousChannelProvider that created the group. If the group parameter is null then the resulting channel is created by the system-wide default provider, and bound to the default group.

Parameters
group AsynchronousChannelGroup: The group to which the newly constructed channel should be bound, or null for the default group

Returns
AsynchronousSocketChannel A new asynchronous socket channel

Throws
ShutdownChannelGroupException If the channel group is shutdown
IOException If an I/O error occurs

open

added in API level 26
public static AsynchronousSocketChannel open ()

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
AsynchronousSocketChannel A new asynchronous socket channel

Throws
IOException If an I/O error occurs

provider

added in API level 26
public final AsynchronousChannelProvider provider ()

Returns the provider that created this channel.

Returns
AsynchronousChannelProvider The provider that created this channel

read

added in API level 26
public abstract Future<Integer> read (ByteBuffer dst)

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.

Parameters
dst ByteBuffer: The buffer into which bytes are to be transferred

Returns
Future<Integer> A Future representing the result of the operation

Throws
IllegalArgumentException
ReadPendingException
NotYetConnectedException If this channel is not yet connected

read

added in API level 26
public final void read (ByteBuffer dst, 
                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.

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.

Parameters
dst ByteBuffer: The buffer into which bytes are to be transferred

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: The completion handler

Throws
IllegalArgumentException
ReadPendingException
NotYetConnectedException If this channel is not yet connected
ShutdownChannelGroupException If the channel group has terminated

read

added in API level 26
public abstract 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.

Parameters
dsts ByteBuffer: The buffers into which bytes are to be transferred

offset int: 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 int: The maximum number of buffers to be accessed; must be non-negative and no larger than dsts.length - offset

timeout long: The maximum time for the I/O operation to complete

unit TimeUnit: The time unit of the timeout argument

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: 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

read

added in API level 26
public abstract 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.

Parameters
dst ByteBuffer: The buffer into which bytes are to be transferred

timeout long: The maximum time for the I/O operation to complete

unit TimeUnit: The time unit of the timeout argument

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: 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

setOption

added in API level 26
public abstract AsynchronousSocketChannel setOption (SocketOption<T> name, 
                T value)

Sets the value of a socket option.

Parameters
name SocketOption: The socket option

value T: The value of the socket option. A value of null may be a valid value for some socket options.

Returns
AsynchronousSocketChannel This channel

Throws
IllegalArgumentException
ClosedChannelException
IOException

shutdownInput

added in API level 26
public abstract AsynchronousSocketChannel shutdownInput ()

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
AsynchronousSocketChannel 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

added in API level 26
public abstract AsynchronousSocketChannel shutdownOutput ()

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
AsynchronousSocketChannel 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

write

added in API level 26
public abstract Future<Integer> write (ByteBuffer src)

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.

Parameters
src ByteBuffer: The buffer from which bytes are to be retrieved

Returns
Future<Integer> A Future representing the result of the operation

Throws
WritePendingException
NotYetConnectedException If this channel is not yet connected

write

added in API level 26
public abstract 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.

Parameters
src ByteBuffer: The buffer from which bytes are to be retrieved

timeout long: The maximum time for the I/O operation to complete

unit TimeUnit: The time unit of the timeout argument

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: 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

added in API level 26
public final void write (ByteBuffer src, 
                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.

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.

Parameters
src ByteBuffer: The buffer from which bytes are to be retrieved

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: The completion handler object

Throws
WritePendingException
NotYetConnectedException If this channel is not yet connected
ShutdownChannelGroupException If the channel group has terminated

write

added in API level 26
public abstract 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.

Parameters
srcs ByteBuffer: The buffers from which bytes are to be retrieved

offset int: 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 int: The maximum number of buffers to be accessed; must be non-negative and no larger than srcs.length - offset

timeout long: The maximum time for the I/O operation to complete

unit TimeUnit: The time unit of the timeout argument

attachment A: The object to attach to the I/O operation; can be null

handler CompletionHandler: 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