NIO中异步IO的完整实现实例

public class SelectSockets {
public static int PORT_NUMBER = 1234;

public static void main(String[] argv) throws Exception {
new SelectSockets().go(argv);
}

public void go(String[] argv) throws Exception {
int port = PORT_NUMBER;
if (argv.length > 0) { // override default listen port
port = Integer.parseInt(argv[0]);
}
System.out.println("Listening on port " + port);
// allocate an unbound server socket channel
ServerSocketChannel serverChannel = ServerSocketChannel.open();
// Get the associated ServerSocket to bind it with
ServerSocket serverSocket = serverChannel.socket();
// set the port the server channel will listen to
serverSocket.bind(new InetSocketAddress(port));
// set non-blocking mode for the listening socket
serverChannel.configureBlocking(false);

// create a new Selector for use below
Selector selector = Selector.open();

// register the ServerSocketChannel with the Selector
serverChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
// this may block for a long time, upon return the
// selected set contains keys of the ready channels
int n = selector.select();
if (n == 0) {
continue; // nothing to do
}
// get an iterator over the set of selected keys
Iterator it = selector.selectedKeys().iterator();
// look at each key in the selected set
while (it.hasNext()) {
SelectionKey key = (SelectionKey) it.next();
// Is a new connection coming in?
if (key.isAcceptable()) {
ServerSocketChannel server = (ServerSocketChannel) key.channel();
SocketChannel channel = server.accept();
registerChannel(selector, channel, SelectionKey.OP_READ);
sayHello(channel);
}
// is there data to read on this channel?
if (key.isReadable()) {
readDataFromSocket(key);
}
// remove key from selected set, it's been handled
it.remove();
}
}
}

// ----------------------------------------------------------
/**
* Register the given channel with the given selector for the given
* operations of interest
*/
protected void registerChannel(Selector selector, SelectableChannel channel, int ops)
throws Exception {
if (channel == null) {
return; // could happen
}
// set the new channel non-blocking
channel.configureBlocking(false);
// register it with the selector
channel.register(selector, ops);
}

// ----------------------------------------------------------
// Use the same byte buffer for all channels. A single thread is
// servicing all the channels, so no danger of concurrent acccess.
private ByteBuffer buffer = ByteBuffer.allocateDirect(1024);

/**
* Sample data handler method for a channel with data ready to read.
*
* @param key
*            A SelectionKey object associated with a channel determined by
*            the selector to be ready for reading. If the channel returns
*            an EOF condition, it is closed here, which automatically
*            invalidates the associated key. The selector will then
*            de-register the channel on the next select call.
*/
protected void readDataFromSocket(SelectionKey key) throws Exception {
SocketChannel socketChannel = (SocketChannel) key.channel();
int count;
buffer.clear(); // make buffer empty
// loop while data available, channel is non-blocking
while ((count = socketChannel.read(buffer)) > 0) {
buffer.flip(); // make buffer readable
// send the data, don't assume it goes all at once
while (buffer.hasRemaining()) {
socketChannel.write(buffer);
}
// WARNING: the above loop is evil. Because
// it's writing back to the same non-blocking
// channel it read the data from, this code can
// potentially spin in a busy loop. In real life
// you'd do something more useful than this.
buffer.clear(); // make buffer empty
}
if (count < 0) {
// close channel on EOF, invalidates the key
socketChannel.close();
}
}

// ----------------------------------------------------------
/**
* Spew a greeting to the incoming client connection.
*
* @param channel
*            The newly connected SocketChannel to say hello to.
*/
private void sayHello(SocketChannel channel) throws Exception {
buffer.clear();
buffer.put("Hi there!\r\n".getBytes());
buffer.flip();
channel.write(buffer);
}
}