设计并实现一个基于字符界面的C/S结构的文件传输程序java代码

以下是一个简单的基于字符界面的C/S结构的文件传输程序的Java代码，仅供参考：

服务端：

import java.io.*;
import java.net.*;

public class FileServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;
        InputStream is = null;
        OutputStream os = null;
        
        try {
            // 创建ServerSocket对象，监听指定端口
            serverSocket = new ServerSocket(8888);
            System.out.println("服务器已启动，等待客户端连接...");
            
            while (true) {
                // 等待客户端连接
                socket = serverSocket.accept();
                System.out.println("客户端已连接：" + socket.getInetAddress().getHostAddress());
                
                // 获取输入输出流
                in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                out = new PrintWriter(socket.getOutputStream(), true);
                is = socket.getInputStream();
                os = socket.getOutputStream();
                
                // 接收文件名和文件大小
                String fileName = in.readLine();
                long fileSize = Long.parseLong(in.readLine());
                System.out.println("接收到文件：" + fileName + "，大小：" + fileSize);
                
                // 创建文件
                File file = new File("D:\\" + fileName);
                if (file.exists()) {
                    out.println("文件已存在");
                    continue;
                } else {
                    out.println("OK");
                }
                
                // 接收文件内容并写入文件
                FileOutputStream fos = new FileOutputStream(file);
                byte[] buffer = new byte[1024];
                int len;
                long receivedSize = 0;
                while (receivedSize < fileSize && (len = is.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                    receivedSize += len;
                }
                fos.close();
                
                // 发送传输完成消息
                out.println("文件传输完成");
                
                // 关闭连接
                socket.close();
                System.out.println("客户端已断开连接：" + socket.getInetAddress().getHostAddress());
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
            if (is != null) is.close();
            if (os != null) os.close();
            if (in != null) in.close();
            if (out != null) out.close();
            if (socket != null) socket.close();
            if (serverSocket != null) serverSocket.close();
        }
    }
}

客户端：

import java.io.*;
import java.net.*;

public class FileClient {
    public static void main(String[] args) throws IOException {
        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;
        InputStream is = null;
        OutputStream os = null;

        try {
            // 创建Socket对象，连接服务端
            socket = new Socket("localhost", 8888);
            System.out.println("连接服务器成功：" + socket.getInetAddress().getHostAddress());

            // 获取输入输出流
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
            is = socket.getInputStream();
            os = socket.getOutputStream();

            // 读取文件名并发送给服务端
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            System.out.print("请输入文件名：");
            String fileName = reader.readLine();
            out.println(fileName);

            // 判断文件是否存在
            String response = in.readLine();
            if ("文件已存在".equals(response)) {
                System.out.println(response);
                return;
            }

            // 读取文件大小并发送给服务端
            System.out.print("请输入文件大小（字节）：");
            long fileSize = Long.parseLong(reader.readLine());
            out.println(fileSize);

            // 读取文件内容并发送给服务端
            FileInputStream fis = new FileInputStream(fileName);
            byte[] buffer = new byte[1024];
            int len;
            long sentSize = 0;
            while (sentSize < fileSize && (len = fis.read(buffer)) != -1) {
                os.write(buffer, 0, len);
                sentSize += len;
            }
            fis.close();

            // 接收传输完成消息
            response = in.readLine();
            System.out.println(response);

            // 关闭连接
            socket.close();
            System.out.println("已断开与服务器的连接");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
            if (is != null) is.close();
            if (os != null) os.close();
            if (in != null) in.close();
            if (out != null) out.close();
            if (socket != null) socket.close();
        }
    }
}

注意：以上代码仅为一个简单的示例，还有许多异常情况未处理，需要根据实际情况进行完善。