Nonblocking I/O - Java Network Programming - page 388

SO_REUSEADDR: false
SO_SNDBUF: 131072
TCP_NODELAY: false
SO_RCVBUF: 131072
UnixAsynchronousServerSocketChannelImpl supports:
SO_REUSEADDR: true
SO_RCVBUF: 131072
DatagramChannelImpl supports:
IP_MULTICAST_TTL: 1
SO_BROADCAST: false
SO_REUSEADDR: false
IP_MULTICAST_IF: null
IP_TOS: 0
IP_MULTICAST_LOOP: true
SO_SNDBUF: 9216
SO_RCVBUF: 196724
Readiness Selection
For network programming, the second part of the new I/O APIs is readiness selection,
the ability to choose a socket that will not block when read or written. This is primarily
of interest to servers, although clients running multiple simultaneous connections with
several windows open—such as a web spider or a browser—can take advantage of it as
well.
In order to perform readiness selection, different channels are registered with a Selec
tor object. Each channel is assigned a SelectionKey . The program can then ask the
Selector object for the set of keys to the channels that are ready to perform the operation
you want to perform without blocking.
The Selector Class
The only constructor in Selector is protected. Normally, a new selector is created by
invoking the static factory method Selector.open() :
public static Selector open () throws IOException
The next step is to add channels to the selector. There are no methods in the Selec
tor class to add a channel. The register() method is declared in the SelectableChan
nel class. Not all channels are selectable—in particular, FileChannel s aren't selectable
—but all network channels are. Thus, the channel is registered with a selector by passing
the selector to one of the channel's register methods:
public final SelectionKey register ( Selector sel , int ops )
throws ClosedChannelException
public final SelectionKey register ( Selector sel , int ops , Object att )
throws ClosedChannelException