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| java.lang.Object
 java.nio.channels.SelectionKey
All known Subclasses: java.nio.channels.spi.AbstractSelectionKey,
| SelectionKey | | abstract public class SelectionKey (Code) | | A token representing the registration of a
SelectableChannel with a
Selector .
A selection key is created each time a channel is registered with a
selector. A key remains valid until it is cancelled by invoking its
SelectionKey.cancel cancel method, by closing its channel, or by closing its
selector. Cancelling a key does not immediately remove it from its
selector; it is instead added to the selector's cancelled-key set for removal during the
next selection operation. The validity of a key may be tested by invoking
its
SelectionKey.isValid isValid method.
A selection key contains two operation sets represented as
integer values. Each bit of an operation set denotes a category of
selectable operations that are supported by the key's channel.
The interest set determines which operation categories will
be tested for readiness the next time one of the selector's selection
methods is invoked. The interest set is initialized with the value given
when the key is created; it may later be changed via the
SelectionKey.interestOps(int) method. The ready set identifies the operation categories for which
the key's channel has been detected to be ready by the key's selector.
The ready set is initialized to zero when the key is created; it may later
be updated by the selector during a selection operation, but it cannot be
updated directly.
That a selection key's ready set indicates that its channel is ready for
some operation category is a hint, but not a guarantee, that an operation in
such a category may be performed by a thread without causing the thread to
block. A ready set is most likely to be accurate immediately after the
completion of a selection operation. It is likely to be made inaccurate by
external events and by I/O operations that are invoked upon the
corresponding channel.
This class defines all known operation-set bits, but precisely which
bits are supported by a given channel depends upon the type of the channel.
Each subclass of
SelectableChannel defines an
SelectableChannel.validOps validOps() method which returns a set
identifying just those operations that are supported by the channel. An
attempt to set or test an operation-set bit that is not supported by a key's
channel will result in an appropriate run-time exception.
It is often necessary to associate some application-specific data with a
selection key, for example an object that represents the state of a
higher-level protocol and handles readiness notifications in order to
implement that protocol. Selection keys therefore support the
attachment of a single arbitrary object to a key. An object can be
attached via the
SelectionKey.attach attach method and then later retrieved via
the
SelectionKey.attachment() attachment method.
Selection keys are safe for use by multiple concurrent threads. The
operations of reading and writing the interest set will, in general, be
synchronized with certain operations of the selector. Exactly how this
synchronization is performed is implementation-dependent: In a naive
implementation, reading or writing the interest set may block indefinitely
if a selection operation is already in progress; in a high-performance
implementation, reading or writing the interest set may block briefly, if at
all. In any case, a selection operation will always use the interest-set
value that was current at the moment that the operation began.
author:
Mark Reinhold
author:
JSR-51 Expert Group
version:
1.33, 07/05/05
since:
1.4
See Also: SelectableChannel
See Also: Selector |
| Field Summary | |
| final public static int | OP_ACCEPT
Operation-set bit for socket-accept operations. | | final public static int | OP_CONNECT
Operation-set bit for socket-connect operations. | | final public static int | OP_READ
Operation-set bit for read operations.
Suppose that a selection key's interest set contains
OP_READ at the start of a selection operation. | | final public static int | OP_WRITE
Operation-set bit for write operations. |
| Constructor Summary | |
| protected | SelectionKey()
Constructs an instance of this class. |
| Method Summary | |
| final public Object | attach(Object ob)
Attaches the given object to this key.
An attached object may later be retrieved via the
SelectionKey.attachment()attachment method. | | final public Object | attachment()
Retrieves the current attachment. | | abstract public void | cancel()
Requests that the registration of this key's channel with its selector
be cancelled. | | abstract public SelectableChannel | channel()
Returns the channel for which this key was created. | | abstract public int | interestOps()
Retrieves this key's interest set.
It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.
This method may be invoked at any time. | | abstract public SelectionKey | interestOps(int ops)
Sets this key's interest set to the given value.
This method may be invoked at any time. | | final public boolean | isAcceptable()
Tests whether this key's channel is ready to accept a new socket
connection.
An invocation of this method of the form k.isAcceptable()
behaves in exactly the same way as the expression
k.readyOps() & OP_ACCEPT != 0
If this key's channel does not support socket-accept operations then
this method always returns false. | | final public boolean | isConnectable()
Tests whether this key's channel has either finished, or failed to
finish, its socket-connection operation.
An invocation of this method of the form k.isConnectable()
behaves in exactly the same way as the expression
k.readyOps() & OP_CONNECT != 0
If this key's channel does not support socket-connect operations
then this method always returns false. | | final public boolean | isReadable()
Tests whether this key's channel is ready for reading.
An invocation of this method of the form k.isReadable()
behaves in exactly the same way as the expression
k.readyOps() & OP_READ != 0
If this key's channel does not support read operations then this
method always returns false. | | abstract public boolean | isValid()
Tells whether or not this key is valid.
A key is valid upon creation and remains so until it is cancelled,
its channel is closed, or its selector is closed. | | final public boolean | isWritable()
Tests whether this key's channel is ready for writing.
An invocation of this method of the form k.isWritable()
behaves in exactly the same way as the expression
k.readyOps() & OP_WRITE != 0
If this key's channel does not support write operations then this
method always returns false. | | abstract public int | readyOps()
Retrieves this key's ready-operation set.
It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel. | | abstract public Selector | selector()
Returns the selector for which this key was created. |
| OP_ACCEPT | | final public static int OP_ACCEPT(Code) | | Operation-set bit for socket-accept operations.
Suppose that a selection key's interest set contains
OP_ACCEPT at the start of a selection operation. If the selector
detects that the corresponding server-socket channel is ready to accept
another connection, or has an error pending, then it will add
OP_ACCEPT to the key's ready set and add the key to its
selected-key set.
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| OP_CONNECT | | final public static int OP_CONNECT(Code) | | Operation-set bit for socket-connect operations.
Suppose that a selection key's interest set contains
OP_CONNECT at the start of a selection operation. If the selector
detects that the corresponding socket channel is ready to complete its
connection sequence, or has an error pending, then it will add
OP_CONNECT to the key's ready set and add the key to its
selected-key set.
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| OP_READ | | final public static int OP_READ(Code) | | Operation-set bit for read operations.
Suppose that a selection key's interest set contains
OP_READ at the start of a selection operation. If the selector
detects that the corresponding channel is ready for reading, has reached
end-of-stream, has been remotely shut down for further reading, or has
an error pending, then it will add OP_READ to the key's
ready-operation set and add the key to its selected-key set.
|
| OP_WRITE | | final public static int OP_WRITE(Code) | | Operation-set bit for write operations.
Suppose that a selection key's interest set contains
OP_WRITE at the start of a selection operation. If the selector
detects that the corresponding channel is ready for writing, has been
remotely shut down for further writing, or has an error pending, then it
will add OP_WRITE to the key's ready set and add the key to its
selected-key set.
|
| SelectionKey | | protected SelectionKey()(Code) | | Constructs an instance of this class.
|
| attach | | final public Object attach(Object ob)(Code) | | Attaches the given object to this key.
An attached object may later be retrieved via the
SelectionKey.attachment()attachment method. Only one object may be attached at a time; invoking
this method causes any previous attachment to be discarded. The current
attachment may be discarded by attaching null.
Parameters:
ob - The object to be attached; may be null The previously-attached object, if any,otherwise null |
| attachment | | final public Object attachment()(Code) | | Retrieves the current attachment.
The object currently attached to this key,or null if there is no attachment |
| cancel | | abstract public void cancel()(Code) | | Requests that the registration of this key's channel with its selector
be cancelled. Upon return the key will be invalid and will have been
added to its selector's cancelled-key set. The key will be removed from
all of the selector's key sets during the next selection operation.
If this key has already been cancelled then invoking this method has
no effect. Once cancelled, a key remains forever invalid.
This method may be invoked at any time. It synchronizes on the
selector's cancelled-key set, and therefore may block briefly if invoked
concurrently with a cancellation or selection operation involving the
same selector.
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| channel | | abstract public SelectableChannel channel()(Code) | | Returns the channel for which this key was created. This method will
continue to return the channel even after the key is cancelled.
This key's channel |
| interestOps | | abstract public int interestOps()(Code) | | Retrieves this key's interest set.
It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.
This method may be invoked at any time. Whether or not it blocks,
and for how long, is implementation-dependent.
This key's interest set
throws:
CancelledKeyException - If this key has been cancelled |
| interestOps | | abstract public SelectionKey interestOps(int ops)(Code) | | Sets this key's interest set to the given value.
This method may be invoked at any time. Whether or not it blocks,
and for how long, is implementation-dependent.
Parameters:
ops - The new interest set This selection key
throws:
IllegalArgumentException - If a bit in the set does not correspond to an operation thatis supported by this key's channel, that is, ifset & ~(channel().validOps()) != 0
throws:
CancelledKeyException - If this key has been cancelled |
| isAcceptable | | final public boolean isAcceptable()(Code) | | Tests whether this key's channel is ready to accept a new socket
connection.
An invocation of this method of the form k.isAcceptable()
behaves in exactly the same way as the expression
k.readyOps() & OP_ACCEPT != 0
If this key's channel does not support socket-accept operations then
this method always returns false.
true if, and only if,readyOps() & OP_ACCEPTis nonzero
throws:
CancelledKeyException - If this key has been cancelled |
| isConnectable | | final public boolean isConnectable()(Code) | | Tests whether this key's channel has either finished, or failed to
finish, its socket-connection operation.
An invocation of this method of the form k.isConnectable()
behaves in exactly the same way as the expression
k.readyOps() & OP_CONNECT != 0
If this key's channel does not support socket-connect operations
then this method always returns false.
true if, and only if,readyOps() & OP_CONNECTis nonzero
throws:
CancelledKeyException - If this key has been cancelled |
| isReadable | | final public boolean isReadable()(Code) | | Tests whether this key's channel is ready for reading.
An invocation of this method of the form k.isReadable()
behaves in exactly the same way as the expression
k.readyOps() & OP_READ != 0
If this key's channel does not support read operations then this
method always returns false.
true if, and only if,readyOps() & OP_READ isnonzero
throws:
CancelledKeyException - If this key has been cancelled |
| isValid | | abstract public boolean isValid()(Code) | | Tells whether or not this key is valid.
A key is valid upon creation and remains so until it is cancelled,
its channel is closed, or its selector is closed.
true if, and only if, this key is valid |
| isWritable | | final public boolean isWritable()(Code) | | Tests whether this key's channel is ready for writing.
An invocation of this method of the form k.isWritable()
behaves in exactly the same way as the expression
k.readyOps() & OP_WRITE != 0
If this key's channel does not support write operations then this
method always returns false.
true if, and only if,readyOps() & OP_WRITEis nonzero
throws:
CancelledKeyException - If this key has been cancelled |
| readyOps | | abstract public int readyOps()(Code) | | Retrieves this key's ready-operation set.
It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.
This key's ready-operation set
throws:
CancelledKeyException - If this key has been cancelled |
| selector | | abstract public Selector selector()(Code) | | Returns the selector for which this key was created. This method will
continue to return the selector even after the key is cancelled.
This key's selector |
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