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深入Java NIO：构建高性能网络应用

article 2025/8/25 0:23:38

引言

在上一篇文章中，我们介绍了Java网络编程的基础模型：阻塞式I/O和线程池模型。这些模型在处理高并发场景时存在明显的局限性。本文将深入探讨Java NIO（New I/O）技术，这是一种能够显著提升网络应用性能的非阻塞I/O模型。

Java NIO的核心概念

Java NIO引入了三个核心组件，彻底改变了传统的I/O编程方式：

Channel（通道）：双向数据传输的通道，替代了传统的Stream
Buffer（缓冲区）：数据的临时存储区域
Selector（选择器）：允许单线程监控多个Channel的状态变化

NIO服务器实现

以下是一个基于NIO的服务器实现，它能够使用单线程处理多个客户端连接：

public class NIOServer {private static final int PORT = 8080;public static void main(String[] args) throws IOException {// 创建ServerSocketChannelServerSocketChannel serverChannel = ServerSocketChannel.open();serverChannel.socket().bind(new InetSocketAddress(PORT));// 设置为非阻塞模式serverChannel.configureBlocking(false);// 创建SelectorSelector selector = Selector.open();// 注册ServerSocketChannel到Selector，关注Accept事件serverChannel.register(selector, SelectionKey.OP_ACCEPT);System.out.println("NIO服务器启动，监听端口：" + PORT);while (true) {// 阻塞等待事件发生，返回就绪的通道数量int readyChannels = selector.select();if (readyChannels == 0) continue;// 获取就绪的SelectionKey集合Set<SelectionKey> selectedKeys = selector.selectedKeys();Iterator<SelectionKey> keyIterator = selectedKeys.iterator();while (keyIterator.hasNext()) {SelectionKey key = keyIterator.next();// 处理就绪的事件if (key.isAcceptable()) {// 有新的连接请求handleAccept(key, selector);} else if (key.isReadable()) {// 有数据可读handleRead(key);}// 从集合中移除已处理的SelectionKeykeyIterator.remove();}}}private static void handleAccept(SelectionKey key, Selector selector) throws IOException {// 获取ServerSocketChannelServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();// 接受客户端连接SocketChannel clientChannel = serverChannel.accept();// 设置为非阻塞模式clientChannel.configureBlocking(false);// 注册到Selector，关注Read事件clientChannel.register(selector, SelectionKey.OP_READ);System.out.println("客户端已连接：" + clientChannel.getRemoteAddress());}private static void handleRead(SelectionKey key) throws IOException {// 获取SocketChannelSocketChannel clientChannel = (SocketChannel) key.channel();// 创建BufferByteBuffer buffer = ByteBuffer.allocate(1024);try {// 读取数据到Bufferint bytesRead = clientChannel.read(buffer);if (bytesRead == -1) {// 客户端关闭连接clientChannel.close();key.cancel();System.out.println("客户端断开连接");return;}// 切换Buffer到读模式buffer.flip();byte[] data = new byte[bytesRead];buffer.get(data);String message = new String(data);System.out.println("收到消息：" + message);// 发送响应ByteBuffer responseBuffer = ByteBuffer.wrap(("服务器回复：" + message).getBytes());clientChannel.write(responseBuffer);} catch (IOException e) {// 处理异常，关闭连接clientChannel.close();key.cancel();System.out.println("读取数据异常：" + e.getMessage());}}
}

NIO客户端实现

public class NIOClient {private static final String HOST = "localhost";private static final int PORT = 8080;public static void main(String[] args) throws IOException {// 创建SocketChannelSocketChannel socketChannel = SocketChannel.open();// 设置为非阻塞模式socketChannel.configureBlocking(false);// 连接服务器socketChannel.connect(new InetSocketAddress(HOST, PORT));// 创建SelectorSelector selector = Selector.open();// 注册连接事件socketChannel.register(selector, SelectionKey.OP_CONNECT);// 创建Scanner读取控制台输入Scanner scanner = new Scanner(System.in);while (true) {// 阻塞等待事件发生selector.select();// 获取就绪的SelectionKey集合Set<SelectionKey> selectedKeys = selector.selectedKeys();Iterator<SelectionKey> keyIterator = selectedKeys.iterator();while (keyIterator.hasNext()) {SelectionKey key = keyIterator.next();if (key.isConnectable()) {// 完成连接SocketChannel channel = (SocketChannel) key.channel();// 完成连接过程if (channel.isConnectionPending()) {channel.finishConnect();}System.out.println("已连接到服务器");// 注册读事件channel.register(selector, SelectionKey.OP_READ);// 启动新线程处理用户输入new Thread(() -> {try {while (true) {System.out.print("请输入消息：");String input = scanner.nextLine();if ("exit".equalsIgnoreCase(input)) {socketChannel.close();System.exit(0);}ByteBuffer buffer = ByteBuffer.wrap(input.getBytes());socketChannel.write(buffer);}} catch (IOException e) {e.printStackTrace();}}).start();} else if (key.isReadable()) {// 处理服务器响应SocketChannel channel = (SocketChannel) key.channel();ByteBuffer buffer = ByteBuffer.allocate(1024);try {int bytesRead = channel.read(buffer);if (bytesRead > 0) {buffer.flip();byte[] data = new byte[bytesRead];buffer.get(data);System.out.println(new String(data));}} catch (IOException e) {System.out.println("读取服务器响应异常：" + e.getMessage());key.cancel();channel.close();}}keyIterator.remove();}}}
}