Nonblocking I/O - Java Network Programming - page 381

Closing
Just as with regular sockets, you should close a channel when you're done with it to free
up the port and any other resources it may be using:
public void close () throws IOException
Closing an already closed channel has no effect. Attempting to write data to or read data
from a closed channel throws an exception. If you're uncertain whether a channel has
been closed, check with isOpen() :
public boolean isOpen ()
Naturally, this returns false if the channel is closed, true if it's open ( close() and
isOpen() are the only two methods declared in the Channel interface and shared by all
channel classes).
Starting in Java 7, SocketChannel implements AutoCloseable , so you can use it in try-
with-resources.
ServerSocketChannel
The ServerSocketChannel class has one purpose: to accept incoming connections. You
cannot read from, write to, or connect a ServerSocketChannel . The only operation it
supports is accepting a new incoming connection. The class itself only declares four
methods, of which accept() is the most important. ServerSocketChannel also inherits
several methods from its superclasses, mostly related to registering with a Selector for
notification of incoming connections. And finally, like all channels, it has a close()
method that shuts down the server socket.
Creating server socket channels
The static factory method ServerSocketChannel.open() creates a new ServerSock
etChannel object. However, the name is a little deceptive. This method does not actually
open a new server socket. Instead, it just creates the object. Before you can use it, you
need to call the socket() method to get the corresponding peer ServerSocket . At this
point, you can configure any server options you like, such as the receive buffer size or
the socket timeout, using the various setter methods in ServerSocket . Then connect
this ServerSocket to a SocketAddress for the port you want to bind to. For example,
this code fragment opens a ServerSocketChannel on port 80:
try {
ServerSocketChannel server = ServerSocketChannel . open ();
ServerSocket socket = serverChannel . socket ();
SocketAddress address = new InetSocketAddress ( 80 );
socket . bind ( address );
} catch ( IOException ex ) {
System . err . println ( "Could not bind to port 80 because " + ex . getMessage ());
}