SocketChannel
abstract class SocketChannel : AbstractSelectableChannel, ByteChannel, ScatteringByteChannel, GatheringByteChannel, NetworkChannel
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:
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 |
SO_LINGER |
Linger on close if data is present (when configured in blocking mode only) |
TCP_NODELAY |
Disable the Nagle algorithm |
Additional (implementation specific) options may also be supported.
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 |
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Initializes a new instance of this class.
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| Public methods |
| abstract SocketChannel! |
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| abstract Boolean |
Connects this channel's socket.
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| abstract Boolean |
Finishes the process of connecting a socket channel.
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| abstract SocketAddress! |
Returns the socket address that this channel's socket is bound to.
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| abstract SocketAddress! |
Returns the remote address to which this channel's socket is connected.
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| abstract Boolean |
Tells whether or not this channel's network socket is connected.
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| abstract Boolean |
Tells whether or not a connection operation is in progress on this channel.
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| open static SocketChannel! |
Opens a socket channel.
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| open static SocketChannel! |
Opens a socket channel and connects it to a remote address.
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| abstract Int |
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| abstract Long |
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| Long |
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| abstract SocketChannel! |
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| abstract SocketChannel! |
Shutdown the connection for reading without closing the channel.
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| abstract SocketChannel! |
Shutdown the connection for writing without closing the channel.
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| abstract Socket! |
Retrieves a socket associated with this channel.
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| Int |
Returns an operation set identifying this channel's supported operations.
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| abstract Int |
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| abstract Long |
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| Long |
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| Inherited functions |
From class AbstractInterruptibleChannel
Unit |
begin()
Marks the beginning of an I/O operation that might block indefinitely.
This method should be invoked in tandem with the end method, using a try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.
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Unit |
close()
Closes this channel.
If the channel has already been closed then this method returns immediately. Otherwise it marks the channel as closed and then invokes the implCloseChannel method in order to complete the close operation.
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Unit |
end(completed: Boolean)
Marks the end of an I/O operation that might block indefinitely.
This method should be invoked in tandem with the begin method, using a try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.
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Unit |
implCloseChannel()
Closes this channel.
This method is invoked by the #close method in order to perform the actual work of closing the channel. This method is only invoked if the channel has not yet been closed, and it is never invoked more than once.
An implementation of this method must arrange for any other thread that is blocked in an I/O operation upon this channel to return immediately, either by throwing an exception or by returning normally.
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Boolean |
isOpen()
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From class AbstractSelectableChannel
Any! |
blockingLock()
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SelectableChannel! |
configureBlocking(block: Boolean)
Adjusts this channel's blocking mode.
If the given blocking mode is different from the current blocking mode then this method invokes the implConfigureBlocking method, while holding the appropriate locks, in order to change the mode.
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Unit |
implCloseChannel()
Closes this channel.
This method, which is specified in the AbstractInterruptibleChannel class and is invoked by the java.nio.channels.Channel#close method, in turn invokes the implCloseSelectableChannel method in order to perform the actual work of closing this channel. It then cancels all of this channel's keys.
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Unit |
implCloseSelectableChannel()
Closes this selectable channel.
This method is invoked by the java.nio.channels.Channel#close method in order to perform the actual work of closing the channel. This method is only invoked if the channel has not yet been closed, and it is never invoked more than once.
An implementation of this method must arrange for any other thread that is blocked in an I/O operation upon this channel to return immediately, either by throwing an exception or by returning normally.
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Unit |
implConfigureBlocking(block: Boolean)
Adjusts this channel's blocking mode.
This method is invoked by the configureBlocking method in order to perform the actual work of changing the blocking mode. This method is only invoked if the new mode is different from the current mode.
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Boolean |
isBlocking()
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Boolean |
isRegistered()
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SelectionKey! |
keyFor(sel: Selector!)
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SelectorProvider! |
provider()
Returns the provider that created this channel.
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SelectionKey! |
register(sel: Selector!, ops: Int, att: Any!)
Registers this channel with the given selector, returning a selection key.
This method first verifies that this channel is open and that the given initial interest set is valid.
If this channel is already registered with the given selector then the selection key representing that registration is returned after setting its interest set to the given value.
Otherwise this channel has not yet been registered with the given selector, so the register method of the selector is invoked while holding the appropriate locks. The resulting key is added to this channel's key set before being returned.
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From class Channel
Unit |
close()
Closes this channel.
After a channel is closed, any further attempt to invoke I/O operations upon it will cause a ClosedChannelException to be thrown.
If this channel is already closed then invoking this method has no effect.
This method may be invoked at any time. If some other thread has already invoked it, however, then another invocation will block until the first invocation is complete, after which it will return without effect.
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Boolean |
isOpen()
Tells whether or not this channel is open.
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From class SelectableChannel
SelectionKey! |
register(sel: Selector!, ops: Int)
Registers this channel with the given selector, returning a selection key.
An invocation of this convenience method of the form
sc.register(sel, ops) behaves in exactly the same way as the invocation sc. register(sel, ops, null)
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Int |
validOps()
Returns an operation set identifying this channel's supported operations. The bits that are set in this integer value denote exactly the operations that are valid for this channel. This method always returns the same value for a given concrete channel class.
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Protected constructors
SocketChannel
protected SocketChannel(provider: SelectorProvider!)
Initializes a new instance of this class.
Public methods
bind
abstract fun bind(local: SocketAddress!): SocketChannel!
| Parameters |
local |
SocketAddress!: The address to bind the socket, or null to bind the socket to an automatically assigned socket address |
| Exceptions |
java.nio.channels.AlreadyBoundException |
If the socket is already bound |
java.nio.channels.UnsupportedAddressTypeException |
If the type of the given address is not supported |
java.nio.channels.ClosedChannelException |
If the channel is closed |
java.io.IOException |
If some other I/O error occurs |
java.lang.SecurityException |
If a security manager has been installed and its checkListen method denies the operation |
java.nio.channels.ConnectionPendingException |
If a non-blocking connect operation is already in progress on this channel |
connect
abstract fun connect(remote: SocketAddress!): Boolean
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 class. That is, if a security manager has been installed then this method verifies that its java.lang.SecurityManager#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 |
| Return |
Boolean |
true if a connection was established, false if this channel is in non-blocking mode and the connection operation is in progress |
| Exceptions |
java.nio.channels.AlreadyConnectedException |
If this channel is already connected |
java.nio.channels.ConnectionPendingException |
If a non-blocking connection operation is already in progress on this channel |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
java.nio.channels.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 |
java.nio.channels.UnresolvedAddressException |
If the given remote address is not fully resolved |
java.nio.channels.UnsupportedAddressTypeException |
If the type of the given remote address is not supported |
java.lang.SecurityException |
If a security manager has been installed and it does not permit access to the given remote endpoint |
java.io.IOException |
If some other I/O error occurs |
finishConnect
abstract fun finishConnect(): Boolean
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 java.io.IOException to be thrown.
If this channel is already connected then this method will not block and will immediately return true. If this channel is in non-blocking mode then this method will return false if the connection process is not yet complete. If this channel is in blocking mode then this method will block until the connection either completes or fails, and will always either return true or throw a checked exception describing the failure.
This method may be invoked at any time. If a read or write operation upon this channel is invoked while an invocation of this method is in progress then that operation will first block until this invocation is complete. If a connection attempt fails, that is, if an invocation of this method throws a checked exception, then the channel will be closed.
| Return |
Boolean |
true if, and only if, this channel's socket is now connected |
| Exceptions |
java.nio.channels.NoConnectionPendingException |
If this channel is not connected and a connection operation has not been initiated |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
java.nio.channels.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 |
java.io.IOException |
If some other I/O error occurs |
getLocalAddress
abstract fun getLocalAddress(): SocketAddress!
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 .
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.
| Return |
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 |
| Exceptions |
java.nio.channels.ClosedChannelException |
If the channel is closed |
java.io.IOException |
If an I/O error occurs |
getRemoteAddress
abstract fun getRemoteAddress(): SocketAddress!
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 .
| Return |
SocketAddress! |
The remote address; null if the channel's socket is not connected |
| Exceptions |
java.nio.channels.ClosedChannelException |
If the channel is closed |
java.io.IOException |
If an I/O error occurs |
isConnected
abstract fun isConnected(): Boolean
Tells whether or not this channel's network socket is connected.
| Return |
Boolean |
true if, and only if, this channel's network socket is open and connected |
isConnectionPending
abstract fun isConnectionPending(): Boolean
Tells whether or not a connection operation is in progress on this channel.
| Return |
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
open static fun open(): SocketChannel!
Opens a socket channel.
The new channel is created by invoking the openSocketChannel method of the system-wide default object.
| Exceptions |
java.io.IOException |
If an I/O error occurs |
open
open static fun open(remote: SocketAddress!): SocketChannel!
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 |
| Exceptions |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the connect operation is in progress |
java.nio.channels.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 |
java.nio.channels.UnresolvedAddressException |
If the given remote address is not fully resolved |
java.nio.channels.UnsupportedAddressTypeException |
If the type of the given remote address is not supported |
java.lang.SecurityException |
If a security manager has been installed and it does not permit access to the given remote endpoint |
java.io.IOException |
If some other I/O error occurs |
read
abstract fun read(dst: ByteBuffer!): Int
| Parameters |
dst |
ByteBuffer!: The buffer into which bytes are to be transferred |
| Return |
Int |
The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream |
| Exceptions |
java.nio.channels.NonReadableChannelException |
If this channel was not opened for reading |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the read operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
read
abstract fun read(
dsts: Array<ByteBuffer!>!,
offset: Int,
length: Int
): Long
| Parameters |
dsts |
Array<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 |
| Return |
Long |
The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream |
| Exceptions |
java.lang.IndexOutOfBoundsException |
If the preconditions on the offset and length parameters do not hold |
java.nio.channels.NonReadableChannelException |
If this channel was not opened for reading |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the read operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
read
fun read(dsts: Array<ByteBuffer!>!): Long
| Parameters |
dsts |
Array<ByteBuffer!>!: The buffers into which bytes are to be transferred |
| Return |
Long |
The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream |
| Exceptions |
java.nio.channels.NonReadableChannelException |
If this channel was not opened for reading |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the read operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
setOption
abstract fun <T : Any!> setOption(
name: SocketOption<T>!,
value: T
): SocketChannel!
| Parameters |
<T> |
The type of the socket option value |
name |
SocketOption<T>!: The socket option |
value |
T: The value of the socket option. A value of null may be a valid value for some socket options. |
| Exceptions |
java.lang.UnsupportedOperationException |
If the socket option is not supported by this channel |
java.lang.IllegalArgumentException |
If the value is not a valid value for this socket option |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.io.IOException |
If an I/O error occurs |
abstract fun shutdownInput(): SocketChannel!
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.
| Exceptions |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.io.IOException |
If some other I/O error occurs |
shutdownOutput
abstract fun shutdownOutput(): SocketChannel!
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.
| Exceptions |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.io.IOException |
If some other I/O error occurs |
socket
abstract fun socket(): Socket!
Retrieves a socket associated with this channel.
The returned object will not declare any public methods that are not declared in the java.net.Socket class.
| Return |
Socket! |
A socket associated with this channel |
write
abstract fun write(src: ByteBuffer!): Int
| Parameters |
src |
ByteBuffer!: The buffer from which bytes are to be retrieved |
| Return |
Int |
The number of bytes written, possibly zero |
| Exceptions |
java.nio.channels.NonWritableChannelException |
If this channel was not opened for writing |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the write operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
write
abstract fun write(
srcs: Array<ByteBuffer!>!,
offset: Int,
length: Int
): Long
| Parameters |
srcs |
Array<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 |
| Return |
Long |
The number of bytes written, possibly zero |
| Exceptions |
java.lang.IndexOutOfBoundsException |
If the preconditions on the offset and length parameters do not hold |
java.nio.channels.NonWritableChannelException |
If this channel was not opened for writing |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the write operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
write
fun write(srcs: Array<ByteBuffer!>!): Long
| Parameters |
srcs |
Array<ByteBuffer!>!: The buffers from which bytes are to be retrieved |
| Return |
Long |
The number of bytes written, possibly zero |
| Exceptions |
java.nio.channels.NonWritableChannelException |
If this channel was not opened for writing |
java.nio.channels.ClosedChannelException |
If this channel is closed |
java.nio.channels.AsynchronousCloseException |
If another thread closes this channel while the write operation is in progress |
java.nio.channels.ClosedByInterruptException |
If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status |
java.io.IOException |
If some other I/O error occurs |
java.nio.channels.NotYetConnectedException |
If this channel is not yet connected |
