NIO中异步IO的完整实现实例

重点是Selector这个类，测试时，启动后，远程登录监听的端口

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 portport = Integer.parseInt(argv[0]);}System.out.println("Listening on port " + port);// allocate an unbound server socket channelServerSocketChannel serverChannel = ServerSocketChannel.open();// Get the associated ServerSocket to bind it withServerSocket serverSocket = serverChannel.socket();// set the port the server channel will listen toserverSocket.bind(new InetSocketAddress(port));// set non-blocking mode for the listening socketserverChannel.configureBlocking(false);// create a new Selector for use belowSelector selector = Selector.open();// register the ServerSocketChannel with the SelectorserverChannel.register(selector, SelectionKey.OP_ACCEPT);while (true) {// this may block for a long time, upon return the// selected set contains keys of the ready channelsint n = selector.select();if (n == 0) {continue; // nothing to do}// get an iterator over the set of selected keysIterator it = selector.selectedKeys().iterator();// look at each key in the selected setwhile (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 handledit.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-blockingchannel.configureBlocking(false);// register it with the selectorchannel.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-blockingwhile ((count = socketChannel.read(buffer)) > 0) {buffer.flip(); // make buffer readable// send the data, don't assume it goes all at oncewhile (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 keysocketChannel.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);}}