SelectableChannel

SelectableChannel

java.nio.channels

---

Java 1.4

closeable

This abstract class defines the API for channels that can be used with a Selector object to allow a thread to block while waiting for activity on any of a group of channels. All channel classes in the java.nio.channels package except for FileChannel are subclasses of SelectableChannel .

A selectable channel may only be registered with a Selector if it is nonblocking, so this class defines the configureBlocking( ) method. Pass false to this method to put a channel into nonblocking mode, or pass TRue to make calls to its read( ) and/or write( ) methods block. Use isBlocking( ) to determine the current blocking mode of a selectable channel.

Register a SelectableChannel with a Selector by calling the register( ) method of the channel (not of the selector). There are two versions of this method: both take a Selector object and a bitmask that specifies the set of channel operations that are to be "selected" on that channel. (see SelectionKey for the constants that can be OR-ed together to form this bitmask). Both methods return a SelectionKey object that represents the registration of the channel with the selector. One version of the register( ) method also takes an arbitrary object argument which serves as an "attachment" to the SelectionKey and allows you to associate arbitrary data with it. The validOps( ) method returns a bitmask that specifies the set of operations that a particular channel object allows to be selected. The bitmask passed to register( ) may only contain bits that are set in this validOps( ) value.

Note that SelectableChannel does not define a deregister ( ) method. Instead, to remove a channel from the set of channels being monitored by a Selector , you must call the cancel( ) method of the SelectionKey returned by register( ) .

Call isRegistered( ) to determine whether a SelectableChannel is registered with any Selector . (Note that a single channel may be registered with more than one Selector .) If you did not keep track of the SelectionKey returned by a call to register( ) , you can query it with the keyFor( ) method.

See Selector and SelectionKey for further details on multiplexing selectable channels.

Figure 13-37. java.nio.channels.SelectableChannel

 public abstract class  SelectableChannel  extends java.nio.channels.spi. AbstractInterruptibleChannel implements Channel {  // Protected Constructors  protected  SelectableChannel  ( );  // Public Instance Methods  public abstract Object  blockingLock  ( );        public abstract SelectableChannel  configureBlocking  (boolean  block  )          throws java.io.IOException;        public abstract boolean  isBlocking  ( );        public abstract boolean  isRegistered  ( );        public abstract SelectionKey  keyFor  (Selector  sel  );        public abstract java.nio.channels.spi.SelectorProvider  provider  ( );        public final SelectionKey  register  (Selector  sel  , int  ops  )          throws ClosedChannelException;        public abstract SelectionKey  register  (Selector  sel  , int  ops  , Object  att  )          throws ClosedChannelException;        public abstract int  validOps  ( );   } 

Subclasses

java.nio.channels.spi.AbstractSelectableChannel

Returned By

SelectionKey.channel( ) , java.nio.channels.spi.AbstractSelectableChannel.configureBlocking( )