java nio tcp服务端接收 文字或者文件，接收到文字时打印，接收到文件时保存到D盘

以下是一个简单的Java NIO TCP服务端代码，可以接收文本和文件：

import java.io.*;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Iterator;
import java.util.Set;

public class NioTcpServer {

    private static final int PORT = 8888;
    private static final int BUFFER_SIZE = 1024;
    private static final Charset CHARSET = StandardCharsets.UTF_8;
    private static final String FILE_SAVE_DIR = "D:\\";

    public static void main(String[] args) throws IOException {
        // 创建 Selector 和 Channel
        Selector selector = Selector.open();
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(PORT));
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        System.out.println("Server started on port " + PORT);

        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()) {
                    // 接收客户端连接请求
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                    System.out.println("Accepted connection from " + socketChannel.getRemoteAddress());
                } else if (key.isReadable()) {
                    // 读取客户端发送的数据
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
                    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
                    int bytesRead;
                    while ((bytesRead = socketChannel.read(buffer)) > 0) {
                        buffer.flip();
                        byte[] bytes = new byte[bytesRead];
                        buffer.get(bytes);
                        byteArrayOutputStream.write(bytes);
                        buffer.clear();
                    }
                    byte[] data = byteArrayOutputStream.toByteArray();
                    byteArrayOutputStream.close();

                    // 判断是文本还是文件
                    if (isTextData(data)) {
                        String text = new String(data, CHARSET);
                        System.out.println("Received text: " + text);
                    } else {
                        String filename = getFilename();
                        Path filePath = Paths.get(FILE_SAVE_DIR, filename);
                        Files.write(filePath, data, StandardOpenOption.CREATE, StandardOpenOption.WRITE);
                        System.out.println("Received file: " + filename);
                    }
                }

                keyIterator.remove();
            }
        }
    }

    /**
     * 判断数据是否为文本
     */
    private static boolean isTextData(byte[] data) {
        return !isBinaryData(data);
    }

    /**
     * 判断数据是否为二进制
     */
    private static boolean isBinaryData(byte[] data) {
        for (byte b : data) {
            if (b < 0x09) return true;
            if (b > 0x0d && b < 0x20) return true;
        }
        return false;
    }

    /**
     * 生成文件名
     */
    private static String getFilename() {
        return "file_" + System.currentTimeMillis();
    }
}

这个服务端会一直监听端口，当有连接请求时接收客户端连接。当客户端发送数据时，服务端会读取数据并判断是文本还是文件，如果是文本则打印，如果是文件则保存到指定目录下。