修正以下代码：import java.io.*; import java.net.ServerSocket; import java.net.Socket; import java.util.HashMap; import java.util.Map; import java.util.Scanner; public class Sever { // 保存所有用户的用户名和密码 private static Map<String, String> userMap = new HashMap<>(); // 指定的目录 private static File rootDir = null; // 保存所有登录的用户信息 private static Map<String, String> loginInfo = new HashMap<>(); public static void main(String[] args) throws Exception { // 从配置文件中读取用户信息和目录信息 BufferedReader reader = new BufferedReader(new FileReader("config.txt")); String line = null; while ((line = reader.readLine()) != null) { if (line.startsWith("user:")) { String[] user = line.split(":"); userMap.put(user[1], user[2]); } if (line.startsWith("dir:")) { String[] dir = line.split(":"); rootDir = new File(dir[1]); } } reader.close(); // 启动服务器 ServerSocket serverSocket = new ServerSocket(8000); int count = 0; System.out.println("服务器启动成功！"); while (true) { // 监听客户端连接 Socket socket = serverSocket.accept(); count++; System.out.println("第" + count + "个客户端连接成功！"); // 处理客户端请求 new Thread(new ServerThread(socket)).start();

以下是代码修正：

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Server {
    // 保存所有用户的用户名和密码
    private static Map<String, String> userMap = new HashMap<>();
    // 指定的目录
    private static File rootDir = null;
    // 保存所有登录的用户信息
    private static Map<String, String> loginInfo = new HashMap<>();

    public static void main(String[] args) throws Exception {
        // 从配置文件中读取用户信息和目录信息
        BufferedReader reader = new BufferedReader(new FileReader("config.txt"));
        String line = null;
        while ((line = reader.readLine()) != null) {
            if (line.startsWith("user:")) {
                String[] user = line.split(":");
                userMap.put(user[1], user[2]);
            }
            if (line.startsWith("dir:")) {
                String[] dir = line.split(":");
                rootDir = new File(dir[1]);
            }
        }
        reader.close();

        // 启动服务器
        ServerSocket serverSocket = new ServerSocket(8000);
        int count = 0;
        System.out.println("服务器启动成功！");
        while (true) {
            // 监听客户端连接
            Socket socket = serverSocket.accept();
            count++;
            System.out.println("第" + count + "个客户端连接成功！");

            // 处理客户端请求
            new Thread(new ServerThread(socket, userMap, rootDir, loginInfo)).start();
        }
    }
}

class ServerThread implements Runnable {
    private Socket socket;
    private Map<String, String> userMap;
    private File rootDir;
    private Map<String, String> loginInfo;

    public ServerThread(Socket socket, Map<String, String> userMap, File rootDir, Map<String, String> loginInfo) {
        this.socket = socket;
        this.userMap = userMap;
        this.rootDir = rootDir;
        this.loginInfo = loginInfo;
    }

    @Override
    public void run() {
        try {
            // 获取输入输出流
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

            // 接收客户端请求
            String request = reader.readLine();
            if (request == null) {
                return;
            }
            System.out.println("客户端请求：" + request);

            // 登录处理
            if (request.startsWith("login:")) {
                String[] login = request.split(":");
                String username = login[1];
                String password = login[2];
                if (userMap.containsKey(username) && userMap.get(username).equals(password)) {
                    loginInfo.put(socket.getInetAddress().getHostAddress(), username);
                    writer.println("login success");
                } else {
                    writer.println("login fail");
                }
            }
            // 列出目录内容处理
            else if (request.equals("list")) {
                String username = loginInfo.get(socket.getInetAddress().getHostAddress());
                if (username == null) {
                    writer.println("not login");
                } else {
                    File[] files = rootDir.listFiles();
                    StringBuilder sb = new StringBuilder();
                    sb.append("total ").append(files.length).append("\n");
                    for (File file : files) {
                        sb.append(file.getName()).append("\n");
                    }
                    writer.println(sb.toString());
                }
            }
            // 下载文件处理
            else if (request.startsWith("get:")) {
                String filename = request.substring(4);
                String username = loginInfo.get(socket.getInetAddress().getHostAddress());
                if (username == null) {
                    writer.println("not login");
                } else {
                    File file = new File(rootDir, filename);
                    if (!file.exists()) {
                        writer.println("file not exist");
                    } else if (!file.isFile()) {
                        writer.println("not a file");
                    } else {
                        writer.println("file start");
                        FileInputStream fis = new FileInputStream(file);
                        byte[] buffer = new byte[1024];
                        int len;
                        while ((len = fis.read(buffer)) != -1) {
                            socket.getOutputStream().write(buffer, 0, len);
                        }
                        fis.close();
                        socket.getOutputStream().flush();
                        writer.println("file end");
                    }
                }
            }
            // 未知请求处理
            else {
                writer.println("unknown request");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

在主程序中，将 ServerThread 构造函数中需要的参数传入，确保 ServerThread 中可以使用这些参数。

在 ServerThread 中，将所有需要使用的变量都作为成员变量传入构造函数中，确保可以在 run 方法中使用。

另外，在处理下载文件请求时，需要将文件内容以字节流的形式写入输出流，否则客户端无法正确接收到文件。