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所以基本上，我想做的是通过我创建的服务器从我的数据库 MySQL 中读取数据。我将数据库中的信息放在一个 ArrayList 中，但客户端无法读取它。当我添加简单的字符串时，它可以工作。但不是当它来自我的数据库时。有什么解决办法吗？

public class Server implements Runnable {

    private ServerSocket server;
    private Socket socket;
    private ObjectOutputStream oos = null;

    public Server() {
        try {
            server = new ServerSocket(4444);
            new Thread(this).start();

        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public void run() {

        System.out.println("Server running");
        while (true) {
            try {
                socket = server.accept();
                sayHi();
                System.out.println("Hallå");
            } catch (Exception e) {
            }
        }
    }

    private void sayHi(){
        DataOutputStream dos;
        try {
            dos = new DataOutputStream(socket.getOutputStream());
            oos = new ObjectOutputStream(socket.getOutputStream());
            dos.writeUTF("Hej");
            sendNames();
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

        public void sendNames() {
            ArrayList<String> drinkar = new ArrayList<String>();

          Connection con = null;
          String url = "jdbc:mysql://localhost:3306/";
          String db = "drycker";
          String driver = "com.mysql.jdbc.Driver";
          String user = "root";
          String pass = "";

          try{
                Class.forName(driver).newInstance();
                con = DriverManager.getConnection(url+db, user, pass);
              try{
                Statement st = (Statement) con.createStatement();
                ResultSet res = st.executeQuery("SELECT * FROM  drinktable");
              while (res.next()) {
                String s = res.getString("Name");
                for(int i = 0; i<drinkar.size(); i++){
                    drinkar.add(s);
                }
              }
                con.close();
              }
              catch (SQLException s){
                System.out.println("SQL code does not execute.");
              }  
              }
              catch (Exception e){
                e.printStackTrace();
              }

        ArrayList<String> a = new ArrayList<String>();
        a.add("Hejsan");
        a.add("Svejsan");
        try {
            FileOutputStream fos = new FileOutputStream("randomList");
            oos = new ObjectOutputStream(fos);
            oos.writeObject(drinkar);
            oos.flush();
            oos.reset();
            oos.close();
            fos.close();

        } catch (Exception e) {

        }

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




public class Client implements Runnable {

    private Socket socket;
    private DataInputStream dis;
    private ObjectInputStream ois = null;

    public Client() {
        socket = new Socket();
        InetSocketAddress ipPort = new InetSocketAddress("192.168.0.10", 4444);
        try {
            socket.connect(ipPort);
            dis = new DataInputStream(socket.getInputStream());
            ois = new ObjectInputStream(socket.getInputStream());
        } catch (Exception e) {
        }
        new Thread(this).start();
    }

    public void run() {
        while (true) {
            try {
                String msg = dis.readUTF();
                if (msg.equals("Hej")) {
                    Thread.sleep(50);
                    receiveArrayList();
                }

            } catch (Exception e) {
            }
        }
    }

    public void receiveArrayList() {

        try {
            FileInputStream fis = new FileInputStream("randomList");
            ois = new ObjectInputStream(fis);
            ArrayList<String> a= (ArrayList<String>) (ois.readObject());
            for(int i = 0; i < a.size(); i++){
                System.out.println((String)a.get(i));
            }

            ois.close();
        } catch (ClassNotFoundException ex) {
            System.out.println(ex);
        } catch (IOException ex) {
            System.out.println(ex);
        }
    }

    public static void main(String[] args) {
        new Client();

    }
}
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