Java网络编程中如何处理并发请求

在Java网络编程中，处理并发请求通常涉及到多线程和异步编程。以下是一些常见的方法来处理并发请求：

1. 多线程：为每个请求创建一个新的线程。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和性能下降。

public class MultiThreadedServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        while (true) {
            Socket socket = serverSocket.accept();
            new Thread(new RequestHandler(socket)).start();
        }
    }
}

class RequestHandler implements Runnable {
    private Socket socket;

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

    @Override
    public void run() {
        // 处理请求
    }
}

2. 线程池：使用线程池来限制同时处理的请求数量。这样可以避免资源耗尽，提高性能。

public class ThreadPoolServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        while (true) {
            Socket socket = serverSocket.accept();
            executorService.submit(new RequestHandler(socket));
        }
    }
}

class RequestHandler implements Runnable {
    private Socket socket;

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

    @Override
    public void run() {
        // 处理请求
    }
}

3. NIO（非阻塞I/O）：使用Java NIO库可以实现非阻塞I/O操作，从而提高性能。NIO提供了Selector和Channel的概念，可以在单个线程中处理多个请求。

public class NIOServer {
    public static void main(String[] args) throws IOException {
        Selector selector = Selector.open();
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8080));
        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()) {
                    SocketChannel socketChannel = ((ServerSocketChannel) key.channel()).accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    // 处理请求
                }
                iterator.remove();
            }
        }
    }
}

4. 异步编程：使用Java 8的CompletableFuture或者第三方库（如Netty）来实现异步编程。这样可以避免阻塞线程，提高性能。

public class AsyncServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        while (true) {
            Socket socket = serverSocket.accept();
            CompletableFuture.runAsync(() -> {
                // 处理请求
            });
        }
    }
}

在实际应用中，可以根据需求和场景选择合适的方法来处理并发请求。对于高并发场景，通常推荐使用NIO或者异步编程。