java nio tcp服务端接收 文字或者图片，接收到文字时打印，接收到图片时保存到D盘

以下是一个简单的 Java NIO TCP 服务端代码，可以接收客户端发送的文字或者图片，并进行相应处理：

import java.io.FileOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;

public class NioTcpServer {

    private static final int BUFFER_SIZE = 1024;
    private static final Charset CHARSET = Charset.forName("UTF-8");

    public static void main(String[] args) throws IOException {
        // 创建 ServerSocketChannel 并绑定到指定端口
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.socket().bind(new InetSocketAddress(8080));
        serverSocketChannel.configureBlocking(false);

        while (true) {
            // 接收客户端连接
            SocketChannel socketChannel = serverSocketChannel.accept();
            if (socketChannel != null) {
                // 处理客户端请求
                handleRequest(socketChannel);
            }
        }
    }

    private static void handleRequest(SocketChannel socketChannel) throws IOException {
        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
        int bytesRead = socketChannel.read(buffer);
        if (bytesRead == -1) {
            // 客户端已关闭连接
            socketChannel.close();
            return;
        }
        buffer.flip();
        byte[] bytes = new byte[buffer.remaining()];
        buffer.get(bytes);
        String message = new String(bytes, CHARSET);
        if (message.startsWith("image:")) {
            // 接收到图片，保存到 D 盘
            String filename = message.substring("image:".length());
            FileOutputStream fos = new FileOutputStream("D:\\" + filename);
            while ((bytesRead = socketChannel.read(buffer)) != -1) {
                buffer.flip();
                fos.write(buffer.array(), 0, bytesRead);
                buffer.clear();
            }
            fos.close();
        } else {
            // 接收到文字，打印
            System.out.println(message);
        }
    }

}

客户端可以使用 telnet 来模拟发送请求：

- 发送文字：`telnet localhost 8080`，然后输入任意文字并回车即可。
- 发送图片：`telnet localhost 8080`，然后输入 `image:filename.jpg`，其中 `filename.jpg` 是图片文件名，然后将图片文件内容拷贝到 telnet 界面中发送即可。