Java网络编程中如何实现并发

在Java网络编程中，实现并发通常涉及以下几种方法：

1. 多线程：为每个客户端连接创建一个新的线程。这种方法简单易懂，但在高并发场景下可能会导致资源耗尽。

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8888);
        while (true) {
            Socket socket = serverSocket.accept();
            new Thread(new ClientHandler(socket)).start();
        }
    }
}

class ClientHandler implements Runnable {
    private Socket socket;

    public ClientHandler(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        // 处理客户端请求
    }
}

2. 线程池：使用线程池来管理线程，可以限制并发线程的数量，避免资源耗尽。

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8888);
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        while (true) {
            Socket socket = serverSocket.accept();
            executorService.submit(new ClientHandler(socket));
        }
    }
}

class ClientHandler implements Runnable {
    private Socket socket;

    public ClientHandler(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        // 处理客户端请求
    }
}

3. NIO（非阻塞I/O）：使用Java NIO库可以实现单线程处理多个客户端连接，提高并发性能。

public class Server {
    public static void main(String[] args) throws IOException {
        Selector selector = Selector.open();
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8888));
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (true) {
            selector.select();
            Set<SelectionKey> selectedKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectedKeys.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                if (key.isAcceptable()) {
                    ServerSocketChannel server = (ServerSocketChannel) key.channel();
                    SocketChannel socketChannel = server.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    // 处理客户端请求
                }
                iterator.remove();
            }
        }
    }
}

4. NIO.2（非阻塞I/O 2）：Java 7引入了NIO.2库，提供了更高级的异步I/O操作，可以更方便地实现高并发。

public class Server {
    public static void main(String[] args) throws IOException {
        AsynchronousServerSocketChannel serverSocketChannel = AsynchronousServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8888));
        serverSocketChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Void>() {
            @Override
            public void completed(AsynchronousSocketChannel socketChannel, Void attachment) {
                serverSocketChannel.accept(null, this);
                // 处理客户端请求
            }

            @Override
            public void failed(Throwable exc, Void attachment) {
                // 处理错误
            }
        });
    }
}

这些方法可以根据实际需求进行选择和组合，以实现Java网络编程中的并发。