AsynchronousSocketChannel

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:

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.

Protected Constructor Summary

AsynchronousSocketChannel(AsynchronousChannelProvider provider) Initializes a new instance of this class.

Public Method Summary

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 Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.nio.channels.AsynchronousByteChannel

abstract <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 Future<Integer>	read(ByteBuffer dst) Reads a sequence of bytes from this channel into the given buffer.
abstract <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 Future<Integer>	write(ByteBuffer src) Writes a sequence of bytes to this channel from the given buffer.

From interface java.nio.channels.NetworkChannel

abstract NetworkChannel	bind(SocketAddress local) Binds the channel's socket to a local address.
abstract SocketAddress	getLocalAddress() Returns the socket address that this channel's socket is bound to.
abstract <T> T	getOption(SocketOption<T> name) Returns the value of a socket option.
abstract <T> NetworkChannel	setOption(SocketOption<T> name, T value) Sets the value of a socket option.
abstract Set<SocketOption<?>>	supportedOptions() Returns a set of the socket options supported by this channel.

From interface java.nio.channels.AsynchronousChannel

abstract void

close() Closes this channel.

From interface java.nio.channels.Channel

abstract void	close() Closes this channel.
abstract boolean	isOpen() Tells whether or not this channel is open.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Protected Constructors

protected AsynchronousSocketChannel (AsynchronousChannelProvider provider)

Initializes a new instance of this class.

Parameters

provider	The provider that created this channel

Public Methods

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	The address to bind the socket, or null to bind the socket to an automatically assigned socket address

Returns

• 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

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

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	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()

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

• 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

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

• 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

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

Returns

• A new asynchronous socket channel

Throws

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

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

• A new asynchronous socket channel

Throws

IOException	If an I/O error occurs

public final AsynchronousChannelProvider provider ()

Returns the provider that created this channel.

Returns

• The provider that created this channel

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	The buffer into which bytes are to be transferred

Returns

• A Future representing the result of the operation

Throws

IllegalArgumentException
ReadPendingException
NotYetConnectedException	If this channel is not yet connected

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

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	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

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	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

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

Sets the value of a socket option.

Parameters

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

Returns

• This channel

Throws

IllegalArgumentException
ClosedChannelException
IOException

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

• 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

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

• 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

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	The buffer from which bytes are to be retrieved

Returns

• A Future representing the result of the operation

Throws

WritePendingException
NotYetConnectedException	If this channel is not yet connected

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	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

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

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	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