Nio学习4——EchoServer在IO，NIO，NIO.2中的实现

堵塞IO实现：

public class PlainEchoServer {
	public void serve(int port) throws IOException {
		final ServerSocket socket = new ServerSocket(port);
		try {
			while (true) {
				final Socket clientSocket = socket.accept();
				System.out.println("Accepted connection from " + clientSocket);
				new Thread(new Runnable() {
					@Override
					public void run() {
						try {
							BufferedReader reader = new BufferedReader(
									new InputStreamReader(
											clientSocket.getInputStream()));
							PrintWriter writer = new PrintWriter(
									clientSocket.getOutputStream(), true);
							while (true) {
								writer.println(reader.readLine());
								writer.flush();
							}
						} catch (IOException e) {
							e.printStackTrace();
							try {
								clientSocket.close();
							} catch (IOException ex) {
								// ignore on close
							}
						}
					}
				}).start();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

非堵塞IO（NIO）实现：

public class PlainNioEchoServer {
	public void serve(int port) throws IOException {
		System.out.println("Listening for connections on port " + port);
		ServerSocketChannel serverChannel = ServerSocketChannel.open();
		ServerSocket ss = serverChannel.socket();
		InetSocketAddress address = new InetSocketAddress(port);
		ss.bind(address);
		serverChannel.configureBlocking(false);
		Selector selector = Selector.open();
		serverChannel.register(selector, SelectionKey.OP_ACCEPT);
		while (true) {
			try {
				selector.select();
			} catch (IOException ex) {
				ex.printStackTrace();
				// handle in a proper way
				break;
			}
			Set readyKeys = selector.selectedKeys();
			Iterator iterator = readyKeys.iterator();
			while (iterator.hasNext()) {
				SelectionKey key = (SelectionKey) iterator.next();
				iterator.remove();
				try {
					if (key.isAcceptable()) {
						ServerSocketChannel server = (ServerSocketChannel) key
								.channel();
						SocketChannel client = server.accept();
						System.out
								.println("Accepted connection from " + client);
						client.configureBlocking(false);
						client.register(selector, SelectionKey.OP_WRITE
								| SelectionKey.OP_READ,
								ByteBuffer.allocate(100));
					}
					if (key.isReadable()) {
						SocketChannel client = (SocketChannel) key.channel();
						ByteBuffer output = (ByteBuffer) key.attachment();
						client.read(output);
					}
					if (key.isWritable()) {
						SocketChannel client = (SocketChannel) key.channel();
						ByteBuffer output = (ByteBuffer) key.attachment();
						output.flip();
						client.write(output);
						output.compact();
					}
				} catch (IOException ex) {
					key.cancel();
					try {
						key.channel().close();
					} catch (IOException cex) {
					}
				}
			}
		}
	}
}

异步IO（NIO.2）实现：

public class PlainNio2EchoServer {
	public void serve(int port) throws IOException {
		System.out.println("Listening for connections on port " + port);
		final AsynchronousServerSocketChannel serverChannel = AsynchronousServerSocketChannel
				.open();
		InetSocketAddress address = new InetSocketAddress(port);
		serverChannel.bind(address);
		final CountDownLatch latch = new CountDownLatch(1);
		serverChannel.accept(null,
				new CompletionHandler<AsynchronousSocketChannel, Object>() {
					@Override
					public void completed(
							final AsynchronousSocketChannel channel,
							Object attachment) {
						serverChannel.accept(null, this);
						ByteBuffer buffer = ByteBuffer.allocate(100);
						channel.read(buffer, buffer, new EchoCompletionHandler(
								channel));
					}

					@Override
					public void failed(Throwable throwable, Object attachment) {
						try {
							serverChannel.close();
						} catch (IOException e) {
							// ingnore on close
						} finally {
							latch.countDown();
						}
					}
				});
		try {
			latch.await();
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt();
		}
	}

	private final class EchoCompletionHandler implements
			CompletionHandler<Integer, ByteBuffer> {
		private final AsynchronousSocketChannel channel;

		EchoCompletionHandler(AsynchronousSocketChannel channel) {
			this.channel = channel;
		}

		@Override
		public void completed(Integer result, ByteBuffer buffer) {
			buffer.flip();
			channel.write(buffer, buffer,
					new CompletionHandler<Integer, ByteBuffer>() {
						@Override
						public void completed(Integer result, ByteBuffer buffer) {
							if (buffer.hasRemaining()) {
								channel.write(buffer, buffer, this);
							} else {
								buffer.compact();
								channel.read(buffer, buffer,
										EchoCompletionHandler.this);
							}
						}

						@Override
						public void failed(Throwable exc, ByteBuffer attachment) {
							try {
								channel.close();
							} catch (IOException e) {
								// ingnore on close
							}
						}
					});
		}

		@Override
		public void failed(Throwable exc, ByteBuffer attachment) {
			try {
				channel.close();
			} catch (IOException e) {
				// ingnore on close
			}
		}
	}
}

At first glance, it may look like more code than what you had when using the previous NIO
implementation. But notice that NIO.2 handles threading and the creation of the so-called
event loop for you. This approach simplifies the code needed to build a multithreaded NIO
application, even though it may not seem to be the case in this example. As the complexity of
the application increases, the gains become more evident because you’ll be producing cleaner
code.