用Nio实现java的客户端和服务端

使用 NIO（Non-blocking I/O）实现 Java 的客户端和服务端可以提高网络通信的效率。下面是一个简单的示例，演示了如何使用 NIO 实现一个简单的客户端和服务端。

首先是服务端代码：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;

public class NioServer {
    private static int BUF_SIZE = 1024;
    private static int PORT = 8080;
    private static int TIMEOUT = 3000;

    public static void main(String[] args) {
        selector();
    }

    public static void handleAccept(SelectionKey key) throws IOException {
        ServerSocketChannel ssChannel = (ServerSocketChannel) key.channel();
        SocketChannel sc = ssChannel.accept();
        sc.configureBlocking(false);
        sc.register(key.selector(), SelectionKey.OP_READ, ByteBuffer.allocateDirect(BUF_SIZE));
    }

    public static void handleRead(SelectionKey key) throws IOException {
        SocketChannel sc = (SocketChannel) key.channel();
        ByteBuffer buf = (ByteBuffer) key.attachment();
        int bytesRead = sc.read(buf);
        while (bytesRead > 0) {
            buf.flip();
            while (buf.hasRemaining()) {
                System.out.print((char) buf.get());
            }
            System.out.println();
            buf.clear();
            bytesRead = sc.read(buf);
        }
        if (bytesRead == -1) {
            sc.close();
        }
    }

    public static void handleWrite(SelectionKey key) throws IOException {
        ByteBuffer buf = (ByteBuffer) key.attachment();
        buf.flip();
        SocketChannel sc = (SocketChannel) key.channel();
        while (buf.hasRemaining()) {
            sc.write(buf);
        }
        buf.compact();
    }

    public static void selector() {
        Selector selector = null;
        ServerSocketChannel ssc = null;
        try {
            selector = Selector.open();
            ssc = ServerSocketChannel.open();
            ssc.socket().bind(new InetSocketAddress(PORT));
            ssc.configureBlocking(false);
            ssc.register(selector, SelectionKey.OP_ACCEPT);
            while (true) {
                if (selector.select(TIMEOUT) == 0) {
                    System.out.println("==");
                    continue;
                }
                Set<SelectionKey> keys = selector.selectedKeys();
                Iterator<SelectionKey> iterator = keys.iterator();
                while (iterator.hasNext()) {
                    SelectionKey key = iterator.next();
                    if (key.isAcceptable()) {
                        handleAccept(key);
                    }
                    if (key.isReadable()) {
                        handleRead(key);
                    }
                    if (key.isWritable() && key.isValid()) {
                        handleWrite(key);
                    }
                    if (key.isConnectable()) {
                        System.out.println("isConnectable = true");
                    }
                    iterator.remove();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (selector != null) {
                    selector.close();
                }
                if (ssc != null) {
                    ssc.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

然后是客户端代码：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;

public class NioClient {
    private static int BUF_SIZE = 1024;
    private static int PORT = 8080;
    private static int TIMEOUT = 3000;

    public static void main(String[] args) throws IOException {
        SocketChannel clientChannel = SocketChannel.open();
        clientChannel.configureBlocking(false);
        Selector selector = Selector.open();
        clientChannel.register(selector, SelectionKey.OP_CONNECT);
        clientChannel.connect(new InetSocketAddress(PORT));
        while (true) {
            if (selector.select(TIMEOUT) == 0) {
                System.out.println("==");
                continue;
            }
            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = keys.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                if (key.isConnectable()) {
                    SocketChannel channel = (SocketChannel) key.channel();
                    if (channel.isConnectionPending()) {
                        channel.finishConnect();
                    }
                    channel.configureBlocking(false);
                    channel.register(selector, SelectionKey.OP_READ);
                    Scanner scanner = new Scanner(System.in);
                    String message = scanner.nextLine();
                    channel.write(ByteBuffer.wrap(message.getBytes()));
                } else if (key.isReadable()) {
                    SocketChannel channel = (SocketChannel) key.channel();
                    ByteBuffer buffer = ByteBuffer.allocate(BUF_SIZE);
                    int bytesRead = channel.read(buffer);
                    while (bytesRead > 0) {
                        buffer.flip();
                        while (buffer.hasRemaining()) {
                            System.out.print((char) buffer.get());
                        }
                        System.out.println();
                        buffer.clear();
                        bytesRead = channel.read(buffer);
                    }
                }
                iterator.remove();
            }
        }
    }
}

这里的服务端监听端口为 8080，客户端连接的端口也为 8080。客户端首先向服务端发送一条消息，然后等待服务端的响应。当服务端接收到客户端的消息后，就会输出到控制台，并将消息原封不动地返回给客户端。客户端接收到服务端的响应后，也会将其输出到控制台。

注意，这个示例只是一个简单的演示，实际开发中需要考虑更多的因素，例如线程安全、异常处理等等。