SocketChannel
public
abstract
class
SocketChannel
extends AbstractSelectableChannel
implements
ByteChannel,
ScatteringByteChannel,
GatheringByteChannel,
NetworkChannel
java.lang.Object | ||||
↳ | java.nio.channels.spi.AbstractInterruptibleChannel | |||
↳ | java.nio.channels.SelectableChannel | |||
↳ | java.nio.channels.spi.AbstractSelectableChannel | |||
↳ | java.nio.channels.SocketChannel |
A selectable channel for stream-oriented connecting sockets.
A socket channel is created by invoking one of the open
methods of this class. It is not possible to create a channel for an arbitrary,
pre-existing socket. A newly-created socket channel is open but not yet
connected. An attempt to invoke an I/O operation upon an unconnected
channel will cause a NotYetConnectedException
to be thrown. A
socket channel can be connected by invoking its 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 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 connect
method for
later completion by the finishConnect
method.
Whether or not a connection operation is in progress may be determined by
invoking the isConnectionPending
method.
Socket channels support asynchronous shutdown, which is similar
to the asynchronous close operation specified in the 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 AsynchronousCloseException
.
Socket options are configured using the setOption
method. Socket channels support the following options:
Additional (implementation specific) options may also be supported.
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 SO_LINGER
Linger on close if data is present (when configured in blocking mode only) TCP_NODELAY
Disable the Nagle algorithm
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 connect
and 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.
Summary
Protected constructors | |
---|---|
SocketChannel(SelectorProvider provider)
Initializes a new instance of this class. |
Public methods | |
---|---|
abstract
SocketChannel
|
bind(SocketAddress local)
Binds the channel's socket to a local address. |
abstract
boolean
|
connect(SocketAddress remote)
Connects this channel's socket. |
abstract
boolean
|
finishConnect()
Finishes the process of connecting a socket channel. |
abstract
SocketAddress
|
getLocalAddress()
Returns the socket address that this channel's socket is bound to.
If there is a security manager set, its |
abstract
SocketAddress
|
getRemoteAddress()
Returns the remote address to which this channel's socket is connected. |
abstract
boolean
|
isConnected()
Tells whether or not this channel's network socket is connected. |
abstract
boolean
|
isConnectionPending()
Tells whether or not a connection operation is in progress on this channel. |
static
SocketChannel
|
open()
Opens a socket channel. |
static
SocketChannel
|
open(SocketAddress remote)
Opens a socket channel and connects it to a remote address. |
abstract
long
|
read(ByteBuffer[] dsts, int offset, int length)
Reads a sequence of bytes from this channel into a subsequence of the given buffers. |
abstract
int
|
read(ByteBuffer dst)
Reads a sequence of bytes from this channel into the given buffer. |
final
long
|
read(ByteBuffer[] dsts)
Reads a sequence of bytes from this channel into the given buffers. |
abstract
<T>
SocketChannel
|
setOption(SocketOption<T> name, T value)
Sets the value of a socket option. |
abstract
SocketChannel
|
shutdownInput()
Shutdown the connection for reading without closing the channel. |
abstract
SocketChannel
|
shutdownOutput()
Shutdown the connection for writing without closing the channel. |
abstract
Socket
|
socket()
Retrieves a socket associated with this channel. |
final
int
|
validOps()
Returns an operation set identifying this channel's supported operations. |
abstract
int
|
write(ByteBuffer src)
Writes a sequence of bytes to this channel from the given buffer. |
final
long
|
write(ByteBuffer[] srcs)
Writes a sequence of bytes to this channel from the given buffers. |
abstract
long
|
write(ByteBuffer[] srcs, int offset, int length)
Writes a sequence of bytes to this channel from a subsequence of the given buffers. |
Inherited methods | |
---|---|
Protected constructors
SocketChannel
protected SocketChannel (SelectorProvider provider)
Initializes a new instance of this class.
Parameters | |
---|---|
provider |
SelectorProvider : The provider that created this channel |
Public methods
bind
public abstract SocketChannel 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 | |
---|---|
SocketChannel |
This channel |
Throws | |
---|---|
ConnectionPendingException |
If a non-blocking connect 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
public abstract boolean connect (SocketAddress remote)
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 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 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.
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.
Parameters | |
---|---|
remote |
SocketAddress : The remote address to which this channel is to be connected |
Returns | |
---|---|
boolean |
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 |
ConnectionPendingException |
If a non-blocking connection operation is already in progress on this channel |
ClosedChannelException |
If this channel is closed |
AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
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 |
UnresolvedAddressException |
If the given remote address is not fully resolved |
UnsupportedAddressTypeException |
If the type of the given remote address is not supported |
SecurityException |
If a security manager has been installed and it does not permit access to the given remote endpoint |
IOException |
If some other I/O error occurs |
finishConnect
public abstract boolean finishConnect ()
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 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
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.
Returns | |
---|---|
boolean |
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 |
ClosedChannelException |
If this channel is closed |
AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
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 |
IOException |
If some other I/O error occurs |
getLocalAddress
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
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 |
isConnected
public abstract boolean isConnected ()
Tells whether or not this channel's network socket is connected.
Returns | |
---|---|
boolean |
true if, and only if, this channel's network socket
is open and connected |
isConnectionPending
public abstract boolean isConnectionPending ()
Tells whether or not a connection operation is in progress on this channel.
Returns | |
---|---|
boolean |
true if, and only if, a connection operation has been
initiated on this channel but not yet completed by invoking the
finishConnect method |
open
public static SocketChannel open ()
Opens a socket channel.
The new channel is created by invoking the openSocketChannel
method of the system-wide default SelectorProvider
object.
Returns | |
---|---|
SocketChannel |
A new socket channel |
Throws | |
---|---|
IOException |
If an I/O error occurs |
open
public static SocketChannel open (SocketAddress remote)
Opens a socket channel and connects it to a remote address.
This convenience method works as if by invoking the open()
method, invoking the connect
method upon
the resulting socket channel, passing it remote
, and then
returning that channel.
Parameters | |
---|---|
remote |
SocketAddress : The remote address to which the new channel is to be connected |
Returns | |
---|---|
SocketChannel |
A new, and connected, socket channel |
Throws | |
---|---|
AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
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 |
UnresolvedAddressException |
If the given remote address is not fully resolved |
UnsupportedAddressTypeException |
If the type of the given remote address is not supported |
SecurityException |
If a security manager has been installed and it does not permit access to the given remote endpoint |
IOException |
If some other I/O error occurs |
read
public abstract long read (ByteBuffer[] dsts, int offset, int length)
Reads a sequence of bytes from this channel into a subsequence of the given buffers.
An invocation of this method attempts to read up to r bytes from this channel, where r is the total number of bytes remaining the specified subsequence of the given buffer array, that is,
at the moment that this method is invoked. dsts[offset].remaining() + dsts[offset+1].remaining() + ... + dsts[offset+length-1].remaining()
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.
This method may be invoked at any time. If another thread has already initiated a read operation upon this channel, however, then an invocation of this method will block until the first operation is complete.
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 |
Returns | |
---|---|
long |
The number of bytes read, possibly zero,
or -1 if the channel has reached end-of-stream |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |
read
public abstract int read (ByteBuffer dst)
Reads a sequence of bytes from this channel into the given buffer.
An attempt is made to 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 moment this method is invoked.
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 this method is
invoked. Upon return the buffer's position will be equal to
p +
n; its limit will not have changed.
A read operation might not fill the buffer, and in fact it might not read any bytes at all. Whether or not it does so depends upon the nature and state of the channel. A socket channel in non-blocking mode, for example, cannot read any more bytes than are immediately available from the socket's input buffer; similarly, a file channel cannot read any more bytes than remain in the file. It is guaranteed, however, that if a channel is in blocking mode and there is at least one byte remaining in the buffer then this method will block until at least one byte is read.
This method may be invoked at any time. If another thread has already initiated a read operation upon this channel, however, then an invocation of this method will block until the first operation is complete.
Parameters | |
---|---|
dst |
ByteBuffer : The buffer into which bytes are to be transferred |
Returns | |
---|---|
int |
The number of bytes read, possibly zero, or -1 if the
channel has reached end-of-stream |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |
read
public final long read (ByteBuffer[] dsts)
Reads a sequence of bytes from this channel into the given buffers.
An invocation of this method of the form c.read(dsts)
behaves in exactly the same manner as the invocation
c.read(dsts, 0, dsts.length);
Parameters | |
---|---|
dsts |
ByteBuffer : The buffers into which bytes are to be transferred |
Returns | |
---|---|
long |
The number of bytes read, possibly zero,
or -1 if the channel has reached end-of-stream |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |
setOption
public abstract SocketChannel 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 | |
---|---|
SocketChannel |
This channel |
Throws | |
---|---|
UnsupportedOperationException |
|
IllegalArgumentException |
|
ClosedChannelException |
|
IOException |
shutdownInput
public abstract SocketChannel 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.
Returns | |
---|---|
SocketChannel |
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 SocketChannel 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.
Returns | |
---|---|
SocketChannel |
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 |
socket
public abstract Socket socket ()
Retrieves a socket associated with this channel.
The returned object will not declare any public methods that are not
declared in the Socket
class.
Returns | |
---|---|
Socket |
A socket associated with this channel |
validOps
public final int validOps ()
Returns an operation set identifying this channel's supported operations.
Socket channels support connecting, reading, and writing, so this
method returns (
SelectionKey#OP_CONNECT
|
SelectionKey#OP_READ
|
SelectionKey.OP_WRITE
)
.
Returns | |
---|---|
int |
The valid-operation set |
write
public abstract int write (ByteBuffer src)
Writes a sequence of bytes to this channel from the given buffer.
An attempt is made to 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 moment this method is invoked.
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 this
method is invoked; the index of the last byte written will be
p +
n -
1
.
Upon return the buffer's position will be equal to
p +
n; its limit will not have changed.
Unless otherwise specified, a write operation will return only after writing all of the r requested bytes. Some types of channels, depending upon their state, may write only some of the bytes or possibly none at all. A socket channel in non-blocking mode, for example, cannot write any more bytes than are free in the socket's output buffer.
This method may be invoked at any time. If another thread has already initiated a write operation upon this channel, however, then an invocation of this method will block until the first operation is complete.
Parameters | |
---|---|
src |
ByteBuffer : The buffer from which bytes are to be retrieved |
Returns | |
---|---|
int |
The number of bytes written, possibly zero |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |
write
public final long write (ByteBuffer[] srcs)
Writes a sequence of bytes to this channel from the given buffers.
An invocation of this method of the form c.write(srcs)
behaves in exactly the same manner as the invocation
c.write(srcs, 0, srcs.length);
Parameters | |
---|---|
srcs |
ByteBuffer : The buffers from which bytes are to be retrieved |
Returns | |
---|---|
long |
The number of bytes written, possibly zero |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |
write
public abstract long write (ByteBuffer[] srcs, int offset, int length)
Writes a sequence of bytes to this channel from a subsequence of the given buffers.
An attempt is made to write 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,
at the moment that this method is invoked. srcs[offset].remaining() + srcs[offset+1].remaining() + ... + srcs[offset+length-1].remaining()
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.
Unless otherwise specified, a write operation will return only after writing all of the r requested bytes. Some types of channels, depending upon their state, may write only some of the bytes or possibly none at all. A socket channel in non-blocking mode, for example, cannot write any more bytes than are free in the socket's output buffer.
This method may be invoked at any time. If another thread has already initiated a write operation upon this channel, however, then an invocation of this method will block until the first operation is complete.
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 |
Returns | |
---|---|
long |
The number of bytes written, possibly zero |
Throws | |
---|---|
NotYetConnectedException |
If this channel is not yet connected |
IOException |