Java in a Nutshell, 5th Edition

Name

Selector

Synopsis

A Selector is an object that monitors multiple nonblocking SelectableChannel objects and (after blocking if necessary) “selects” the channel that is (or the channels that are) ready for I/O. Create a new Selector with the static open( ) method. Next register the channels that it is to monitor: a channel is registered by passing the Selector to the register( ) method of the channel (register( ) is defined by the abstract SelectableChannel class). In addition to the Selector you must also pass a bitmask that specifies which I/O operations (reading, writing, connecting, and accepting) that the Selector is to monitor for that channel. Each call to this register( ) method returns a SelectionKey object. (The SelectionKey class also defines the constants that are used to form the bitmask of I/O operations.) Note that before a SelectableChannel can be registered, it must be in nonblocking mode, which can be accomplished with the configureBlocking( ) method of SelectableChannel.

Once the channels are registered with the Selector, call select( ) to block until one or more of the channels is ready for I/O. One version of select( ) takes a timeout value and returns if the specified number of milliseconds elapses without any channels becoming ready for I/O. These methods also return if any of the channels is closed, if an error occurs on any channel, if the wakeup( ) method of the Selector is called, or if the interrupt( ) method of the blocked thread is called. There is ...