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java.nio.channels
Class SelectableChannel

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.nio.channels.spi.AbstractInterruptibleChannel sample code for java.nio.channels.spi.AbstractInterruptibleChannel definition code for java.nio.channels.spi.AbstractInterruptibleChannel 
      extended by java.nio.channels.SelectableChannel
All Implemented Interfaces:
Closeable sample code for java.io.Closeable definition code for java.io.Closeable , Channel sample code for java.nio.channels.Channel definition code for java.nio.channels.Channel , InterruptibleChannel sample code for java.nio.channels.InterruptibleChannel definition code for java.nio.channels.InterruptibleChannel
Direct Known Subclasses:
AbstractSelectableChannel sample code for java.nio.channels.spi.AbstractSelectableChannel definition code for java.nio.channels.spi.AbstractSelectableChannel 
public abstract class SelectableChannel
extends AbstractInterruptibleChannel sample code for java.nio.channels.spi.AbstractInterruptibleChannel definition code for java.nio.channels.spi.AbstractInterruptibleChannel 
implements Channel sample code for java.nio.channels.Channel definition code for java.nio.channels.Channel

A channel that can be multiplexed via a Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector .

In order to be used with a selector, an instance of this class must first be registered via the register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) method. This method returns a new SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey object that represents the channel's registration with the selector.

Once registered with a selector, a channel remains registered until it is deregistered. This involves deallocating whatever resources were allocated to the channel by the selector.

A channel cannot be deregistered directly; instead, the key representing its registration must be cancelled. Cancelling a key requests that the channel be deregistered during the selector's next selection operation. A key may be cancelled explicitly by invoking its cancel sample code for java.nio.channels.SelectionKey.cancel() definition code for java.nio.channels.SelectionKey.cancel() method. All of a channel's keys are cancelled implicitly when the channel is closed, whether by invoking its close sample code for java.nio.channels.Channel.close() definition code for java.nio.channels.Channel.close() method or by interrupting a thread blocked in an I/O operation upon the channel.

If the selector itself is closed then the channel will be deregistered, and the key representing its registration will be invalidated, without further delay.

A channel may be registered at most once with any particular selector.

Whether or not a channel is registered with one or more selectors may be determined by invoking the isRegistered sample code for java.nio.channels.SelectableChannel.isRegistered() definition code for java.nio.channels.SelectableChannel.isRegistered() method.

Selectable channels are safe for use by multiple concurrent threads.

Blocking mode

A selectable channel is either in blocking mode or in non-blocking mode. In blocking mode, every I/O operation invoked upon the channel will block until it completes. In non-blocking mode an I/O operation will never block and may transfer fewer bytes than were requested or possibly no bytes at all. The blocking mode of a selectable channel may be determined by invoking its isBlocking sample code for java.nio.channels.SelectableChannel.isBlocking() definition code for java.nio.channels.SelectableChannel.isBlocking() method.

Newly-created selectable channels are always in blocking mode. Non-blocking mode is most useful in conjunction with selector-based multiplexing. A channel must be placed into non-blocking mode before being registered with a selector, and may not be returned to blocking mode until it has been deregistered.

Since:
1.4
See Also:
SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey , Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector

Constructor Summary
protected SelectableChannel sample code for java.nio.channels.SelectableChannel.SelectableChannel() definition code for java.nio.channels.SelectableChannel.SelectableChannel() ()
          Initializes a new instance of this class.
 
Method Summary
abstract  Object sample code for java.lang.Object definition code for java.lang.Object blockingLock sample code for java.nio.channels.SelectableChannel.blockingLock() definition code for java.nio.channels.SelectableChannel.blockingLock() ()
          Retrieves the object upon which the configureBlocking sample code for java.nio.channels.SelectableChannel.configureBlocking(boolean) definition code for java.nio.channels.SelectableChannel.configureBlocking(boolean) and register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) methods synchronize.
abstract  SelectableChannel sample code for java.nio.channels.SelectableChannel definition code for java.nio.channels.SelectableChannel configureBlocking sample code for java.nio.channels.SelectableChannel.configureBlocking(boolean) definition code for java.nio.channels.SelectableChannel.configureBlocking(boolean) (boolean block)
          Adjusts this channel's blocking mode.
abstract  boolean isBlocking sample code for java.nio.channels.SelectableChannel.isBlocking() definition code for java.nio.channels.SelectableChannel.isBlocking() ()
          Tells whether or not every I/O operation on this channel will block until it completes.
abstract  boolean isRegistered sample code for java.nio.channels.SelectableChannel.isRegistered() definition code for java.nio.channels.SelectableChannel.isRegistered() ()
          Tells whether or not this channel is currently registered with any selectors.
abstract  SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey keyFor sample code for java.nio.channels.SelectableChannel.keyFor(java.nio.channels.Selector) definition code for java.nio.channels.SelectableChannel.keyFor(java.nio.channels.Selector) (Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel)
          Retrieves the key representing the channel's registration with the given selector.
abstract  SelectorProvider sample code for java.nio.channels.spi.SelectorProvider definition code for java.nio.channels.spi.SelectorProvider provider sample code for java.nio.channels.SelectableChannel.provider() definition code for java.nio.channels.SelectableChannel.provider() ()
          Returns the provider that created this channel.
 SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) (Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel, int ops)
          Registers this channel with the given selector, returning a selection key.
abstract  SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) (Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel, int ops, Object sample code for java.lang.Object definition code for java.lang.Object  att)
          Registers this channel with the given selector, returning a selection key.
abstract  int validOps sample code for java.nio.channels.SelectableChannel.validOps() definition code for java.nio.channels.SelectableChannel.validOps() ()
          Returns an operation set identifying this channel's supported operations.
 
Methods inherited from class java.nio.channels.spi.AbstractInterruptibleChannel sample code for java.nio.channels.spi.AbstractInterruptibleChannel definition code for java.nio.channels.spi.AbstractInterruptibleChannel
begin sample code for java.nio.channels.spi.AbstractInterruptibleChannel.begin() definition code for java.nio.channels.spi.AbstractInterruptibleChannel.begin() , close sample code for java.nio.channels.spi.AbstractInterruptibleChannel.close() definition code for java.nio.channels.spi.AbstractInterruptibleChannel.close() , end sample code for java.nio.channels.spi.AbstractInterruptibleChannel.end(boolean) definition code for java.nio.channels.spi.AbstractInterruptibleChannel.end(boolean) , implCloseChannel sample code for java.nio.channels.spi.AbstractInterruptibleChannel.implCloseChannel() definition code for java.nio.channels.spi.AbstractInterruptibleChannel.implCloseChannel() , isOpen sample code for java.nio.channels.spi.AbstractInterruptibleChannel.isOpen() definition code for java.nio.channels.spi.AbstractInterruptibleChannel.isOpen()
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() , equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , toString sample code for java.lang.Object.toString() definition code for java.lang.Object.toString() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 
Methods inherited from interface java.nio.channels.Channel sample code for java.nio.channels.Channel definition code for java.nio.channels.Channel
close sample code for java.nio.channels.Channel.close() definition code for java.nio.channels.Channel.close() , isOpen sample code for java.nio.channels.Channel.isOpen() definition code for java.nio.channels.Channel.isOpen()
 

Constructor Detail

SelectableChannel sample code for java.nio.channels.SelectableChannel() definition code for java.nio.channels.SelectableChannel() 

protected SelectableChannel()
Initializes a new instance of this class.

Method Detail

provider sample code for java.nio.channels.SelectableChannel.provider() definition code for java.nio.channels.SelectableChannel.provider() 

public abstract SelectorProvider sample code for java.nio.channels.spi.SelectorProvider definition code for java.nio.channels.spi.SelectorProvider  provider()
Returns the provider that created this channel.

Returns:
The provider that created this channel

validOps sample code for java.nio.channels.SelectableChannel.validOps() definition code for java.nio.channels.SelectableChannel.validOps() 

public abstract 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.

Returns:
The valid-operation set

isRegistered sample code for java.nio.channels.SelectableChannel.isRegistered() definition code for java.nio.channels.SelectableChannel.isRegistered() 

public abstract boolean isRegistered()
Tells whether or not this channel is currently registered with any selectors. A newly-created channel is not registered.

Due to the inherent delay between key cancellation and channel deregistration, a channel may remain registered for some time after all of its keys have been cancelled. A channel may also remain registered for some time after it is closed.

Returns:
true if, and only if, this channel is registered

keyFor sample code for java.nio.channels.SelectableChannel.keyFor(java.nio.channels.Selector) definition code for java.nio.channels.SelectableChannel.keyFor(java.nio.channels.Selector) 

public abstract SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey  keyFor(Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel)
Retrieves the key representing the channel's registration with the given selector.

Returns:
The key returned when this channel was last registered with the given selector, or null if this channel is not currently registered with that selector

register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) 

public abstract SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey  register(Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel,
                                      int ops,
                                      Object sample code for java.lang.Object definition code for java.lang.Object  att)
                               throws ClosedChannelException sample code for java.nio.channels.ClosedChannelException definition code for java.nio.channels.ClosedChannelException
Registers this channel with the given selector, returning a selection key.

If this channel is currently registered with the given selector then the selection key representing that registration is returned. The key's interest set will have been changed to ops, as if by invoking the interestOps(int) sample code for java.nio.channels.SelectionKey.interestOps(int) definition code for java.nio.channels.SelectionKey.interestOps(int) method. If the att argument is not null then the key's attachment will have been set to that value. A CancelledKeyException sample code for java.nio.channels.CancelledKeyException definition code for java.nio.channels.CancelledKeyException will be thrown if the key has already been cancelled.

Otherwise this channel has not yet been registered with the given selector, so it is registered and the resulting new key is returned. The key's initial interest set will be ops and its attachment will be att.

This method may be invoked at any time. If this method is invoked while another invocation of this method or of the configureBlocking sample code for java.nio.channels.SelectableChannel.configureBlocking(boolean) definition code for java.nio.channels.SelectableChannel.configureBlocking(boolean) method is in progress then it will first block until the other operation is complete. This method will then synchronize on the selector's key set and therefore may block if invoked concurrently with another registration or selection operation involving the same selector.

If this channel is closed while this operation is in progress then the key returned by this method will have been cancelled and will therefore be invalid.

Parameters:
sel - The selector with which this channel is to be registered
ops - The interest set for the resulting key
att - The attachment for the resulting key; may be null
Returns:
A key representing the registration of this channel with the given selector
Throws:
ClosedChannelException sample code for java.nio.channels.ClosedChannelException definition code for java.nio.channels.ClosedChannelException - If this channel is closed
IllegalBlockingModeException sample code for java.nio.channels.IllegalBlockingModeException definition code for java.nio.channels.IllegalBlockingModeException - If this channel is in blocking mode
IllegalSelectorException sample code for java.nio.channels.IllegalSelectorException definition code for java.nio.channels.IllegalSelectorException - If this channel was not created by the same provider as the given selector
CancelledKeyException sample code for java.nio.channels.CancelledKeyException definition code for java.nio.channels.CancelledKeyException - If this channel is currently registered with the given selector but the corresponding key has already been cancelled
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - If a bit in the ops set does not correspond to an operation that is supported by this channel, that is, if set & ~validOps() != 0

register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) 

public final SelectionKey sample code for java.nio.channels.SelectionKey definition code for java.nio.channels.SelectionKey  register(Selector sample code for java.nio.channels.Selector definition code for java.nio.channels.Selector  sel,
                                   int ops)
                            throws ClosedChannelException sample code for java.nio.channels.ClosedChannelException definition code for java.nio.channels.ClosedChannelException
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 sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) (sel, ops, null)

Parameters:
sel - The selector with which this channel is to be registered
ops - The interest set for the resulting key
Returns:
A key representing the registration of this channel with the given selector
Throws:
ClosedChannelException sample code for java.nio.channels.ClosedChannelException definition code for java.nio.channels.ClosedChannelException - If this channel is closed
IllegalBlockingModeException sample code for java.nio.channels.IllegalBlockingModeException definition code for java.nio.channels.IllegalBlockingModeException - If this channel is in blocking mode
IllegalSelectorException sample code for java.nio.channels.IllegalSelectorException definition code for java.nio.channels.IllegalSelectorException - If this channel was not created by the same provider as the given selector
CancelledKeyException sample code for java.nio.channels.CancelledKeyException definition code for java.nio.channels.CancelledKeyException - If this channel is currently registered with the given selector but the corresponding key has already been cancelled
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - If a bit in ops does not correspond to an operation that is supported by this channel, that is, if set & ~validOps() != 0

configureBlocking sample code for java.nio.channels.SelectableChannel.configureBlocking(boolean) definition code for java.nio.channels.SelectableChannel.configureBlocking(boolean) 

public abstract SelectableChannel sample code for java.nio.channels.SelectableChannel definition code for java.nio.channels.SelectableChannel  configureBlocking(boolean block)
                                             throws IOException sample code for java.io.IOException definition code for java.io.IOException
Adjusts this channel's blocking mode.

If this channel is registered with one or more selectors then an attempt to place it into blocking mode will cause an IllegalBlockingModeException sample code for java.nio.channels.IllegalBlockingModeException definition code for java.nio.channels.IllegalBlockingModeException to be thrown.

This method may be invoked at any time. The new blocking mode will only affect I/O operations that are initiated after this method returns. For some implementations this may require blocking until all pending I/O operations are complete.

If this method is invoked while another invocation of this method or of the register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int) method is in progress then it will first block until the other operation is complete.

Parameters:
block - If true then this channel will be placed in blocking mode; if false then it will be placed non-blocking mode
Returns:
This selectable channel
Throws:
ClosedChannelException sample code for java.nio.channels.ClosedChannelException definition code for java.nio.channels.ClosedChannelException - If this channel is closed
IllegalBlockingModeException sample code for java.nio.channels.IllegalBlockingModeException definition code for java.nio.channels.IllegalBlockingModeException - If block is true and this channel is registered with one or more selectors
IOException sample code for java.io.IOException definition code for java.io.IOException - If an I/O error occurs

isBlocking sample code for java.nio.channels.SelectableChannel.isBlocking() definition code for java.nio.channels.SelectableChannel.isBlocking() 

public abstract boolean isBlocking()
Tells whether or not every I/O operation on this channel will block until it completes. A newly-created channel is always in blocking mode.

If this channel is closed then the value returned by this method is not specified.

Returns:
true if, and only if, this channel is in blocking mode

blockingLock sample code for java.nio.channels.SelectableChannel.blockingLock() definition code for java.nio.channels.SelectableChannel.blockingLock() 

public abstract Object sample code for java.lang.Object definition code for java.lang.Object  blockingLock()
Retrieves the object upon which the configureBlocking sample code for java.nio.channels.SelectableChannel.configureBlocking(boolean) definition code for java.nio.channels.SelectableChannel.configureBlocking(boolean) and register sample code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) definition code for java.nio.channels.SelectableChannel.register(java.nio.channels.Selector, int, java.lang.Object) methods synchronize. This is often useful in the implementation of adaptors that require a specific blocking mode to be maintained for a short period of time.

Returns:
The blocking-mode lock object
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