如何实现NIO模型中的服务器端和客户端代码交互？

NIO模型的服务器端和客户端代码主要包括以下几个部分：，，1. 创建ServerSocketChannel和Selector，绑定端口并监听连接请求。，2. 创建SocketChannel并注册到Selector上，监听OP_READ事件。，3. 通过Selector的select()方法阻塞等待就绪事件。，4. 遍历就绪事件，处理读、写等操作。，5. 关闭连接和释放资源。，，客户端代码与服务器端类似，主要区别在于客户端需要主动发起连接请求。

在NIO模型中，服务器端和客户端的代码实现都遵循非阻塞I/O操作的原则，以下是一个简单的NIO服务器端和客户端的代码示例。

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1. NIO服务器端代码

1.1 创建选择器和通道

我们创建一个Selector和一个监听特定端口的ServerSocketChannel。

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;
public class NIOServer {
    public static void main(String[] args) throws IOException {
        // 创建选择器
        Selector selector = Selector.open();
        // 创建ServerSocketChannel
        ServerSocketChannel serverSocket = ServerSocketChannel.open();
        InetSocketAddress address = new InetSocketAddress("localhost", 9090);
        serverSocket.bind(address);
        serverSocket.configureBlocking(false);
        SelectionKey selectorKey = serverSocket.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("Server started on port 9090");
        // 主循环，处理事件
        while (true) {
            int readyChannels = selector.select();
            if (readyChannels == 0) continue;
            Set<SelectionKey> selectedKeys = selector.selectedKeys();
            Iterator<SelectionKey> keyIterator = selectedKeys.iterator();
            while (keyIterator.hasNext()) {
                SelectionKey key = keyIterator.next();
                if (key.isAcceptable()) {
                    // 接受新连接
                    handleAccept(serverSocket, selector);
                } else if (key.isReadable()) {
                    // 读取数据
                    handleRead(key);
                }
                keyIterator.remove();
            }
        }
    }
}

1.2 处理新连接和读取数据

我们需要实现handleAccept和handleRead方法来处理新的连接请求和读取数据。

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static void handleAccept(ServerSocketChannel serverSocket, Selector selector) throws IOException {
    SocketChannel client = serverSocket.accept();
    client.configureBlocking(false);
    client.register(selector, SelectionKey.OP_READ);
    System.out.println("New connection accepted: " + client.getRemoteAddress());
}
static void handleRead(SelectionKey key) throws IOException {
    SocketChannel client = (SocketChannel) key.channel();
    ByteBuffer buffer = ByteBuffer.allocate(1024);
    int bytesRead = client.read(buffer);
    if (bytesRead == 1) {
        client.close();
    } else {
        buffer.flip();
        // 在这里可以对读取到的数据进行处理
        System.out.println("Data read from client: " + new String(buffer.array(), StandardCharsets.UTF_8));
    }
}

2. NIO客户端代码

2.1 创建选择器和通道

对于客户端，我们也需要创建一个Selector和一个SocketChannel。

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;
public class NIOClient {
    public static void main(String[] args) throws IOException {
        // 创建选择器和通道
        Selector selector = Selector.open();
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.configureBlocking(false);
        socketChannel.connect(new InetSocketAddress("localhost", 9090));
        socketChannel.register(selector, SelectionKey.OP_CONNECT);
        // 主循环，处理事件
        while (true) {
            int readyChannels = selector.select();
            if (readyChannels == 0) continue;
            Set<SelectionKey> selectedKeys = selector.selectedKeys();
            Iterator<SelectionKey> keyIterator = selectedKeys.iterator();
            while (keyIterator.hasNext()) {
                SelectionKey key = keyIterator.next();
                if (key.isConnectable()) {
                    // 完成连接过程
                    connect(socketChannel);
                } else if (key.isWritable()) {
                    // 写入数据
                    write(socketChannel);
                }
                keyIterator.remove();
            }
        }
    }
}

2.2 完成连接和写入数据

实现connect和write方法来完成连接过程和发送数据。

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static void connect(SocketChannel socketChannel) throws IOException {
    if (socketChannel.isConnectionPending()) {
        while (!socketChannel.finishConnect()) {
            // wait, or do something else...
        }
        System.out.println("Connected to server");
    }
    socketChannel.configureBlocking(false);
    socketChannel.register(Selector.open(), SelectionKey.OP_WRITE);
}
static void write(SocketChannel socketChannel) throws IOException {
    String message = "Hello from client!";
    ByteBuffer buffer = ByteBuffer.allocate(1024);
    buffer.put(message.getBytes(StandardCharsets.UTF_8));
    buffer.flip();
    while (buffer.hasRemaining()) {
        socketChannel.write(buffer);
    }
    buffer.clear();
    System.out.println("Message sent to server: " + message);
}