服务器自动从用户那里获取输入，而不是在Java中等待

Question

更新：我尝试硬编码密码并让用户输入，它只是跳过了输入部分，如下所示：

Please press one to sign in or two to sign up if you haven't already1
Please enter your credentials below
Username:
Password:
Your username and/or password are incorrect, access has been denied

import java.io.*;
import java.net.*;
import java.util.Scanner;

public class MultipleClient {
    public static void main(String[] args) throws IOException {
        try {
            Scanner scan = new Scanner(System.in);

            InetAddress ip = InetAddress.getByName("localhost");

            Socket socket = new Socket(ip, 8189);

            // Receiving input and sending output to Server
            DataInputStream inputFromServer = new DataInputStream(socket.getInputStream());
            DataOutputStream outputToServer = new DataOutputStream(socket.getOutputStream());

            while (true) {

                System.out.println(inputFromServer.readUTF());
                int choice = scan.nextInt();
                outputToServer.writeInt(choice);
                System.out.println(inputFromServer.readUTF());
                String username = scan.nextLine();
                outputToServer.writeUTF(username);
                System.out.println(inputFromServer.readUTF());
                String password = scan.nextLine();
                outputToServer.writeUTF(password);
                System.out.println(inputFromServer.readUTF());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import java.io.*;
import java.text.*;
import java.util.*;
import java.net.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;

public class MultipleServer {
    public static void main(String[] args) throws IOException {
        Scanner scan = new Scanner(System.in);
        ServerSocket serverSocket = new ServerSocket(8189);

        // Server keeps on receiving new Clients
        while (true) {
            Socket clientSocket = null;
            try {
                // ServerSocket waits for a Client to connect
                clientSocket = serverSocket.accept();

                System.out.println("A new client is connected : " + clientSocket);

                // Receiving input and sending output to Client
                DataInputStream inputFromClient = new DataInputStream(clientSocket.getInputStream());
                DataOutputStream outputToClient = new DataOutputStream(clientSocket.getOutputStream());

                System.out.println("Assigning new thread for this client");

                System.out
                        .println("-----------------------------------------------------------------------------------");

                // Create a new Thread object for the Client
                Thread thread = new ClientHandler(clientSocket, inputFromClient, outputToClient);
                thread.start();

            } catch (Exception e) {
                clientSocket.close();
                e.printStackTrace();
            }
        }
    }
}

// ClientHandler class
class ClientHandler extends Thread {
    final Socket clientSocket;
    final DataInputStream inputFromClient;
    final DataOutputStream outputToClient;

    // Constructor
    public ClientHandler(Socket clientSocket, DataInputStream inputFromClient, DataOutputStream outputToClient) {
        this.clientSocket = clientSocket;
        this.inputFromClient = inputFromClient;
        this.outputToClient = outputToClient;
    }

    @Override
    public void run() {
        // Variables
        String Username = "";
        String Password = "";
        int choice;
        String toreturn;
        while (true) {
            try {
                // The newInstance() call is a work around for some
                // broken Java implementations

                Class.forName("com.mysql.cj.jdbc.Driver").newInstance();
            } catch (Exception ex) {
                // handle the error
            }

            Connection conn = null;

            try {
                conn = DriverManager.getConnection(
                        "jdbc:mysql://localhost:3306/test" + "?user=root&password=test");

            } catch (SQLException ex) {
                // handle any errors
                System.out.println("SQLException: " + ex.getMessage());
                System.out.println("SQLState: " + ex.getSQLState());
                System.out.println("VendorError: " + ex.getErrorCode());
            }

            try {

                outputToClient.writeUTF("Please press one to sign in or two to sign up if you haven't already");
                choice = inputFromClient.readInt();

                if (choice != 1 && choice != 0) {
                    outputToClient.writeUTF("Please choose one of the listed choices");
                } else {
                    if (choice == 1) {
//here is where the problem is occuring
                        outputToClient.writeUTF("Please enter your credentials below\n");
                        outputToClient.writeUTF("Username:");
                        Username = inputFromClient.readUTF();
                        outputToClient.writeUTF("Password:");
                        Password = inputFromClient.readUTF();
                        String queryoneresult = "";

//execution isn't reaching this part so I don't think it is relevant but I included it anyway
                        ResultSet rs = null;

                        PreparedStatement stmt = conn
                                .prepareStatement("SELECT COUNT(Username)\n" + "  FROM Authentication\n"
                                        + " WHERE Username = ? AND\n" + "       Password = ? \n" + " LIMIT 0, 1");
                        stmt.setString(1, Username);
                        stmt.setString(2, Password);

                        rs = stmt.executeQuery();

                        if (stmt.execute()) {
                            rs = stmt.getResultSet();
                        }
                        ResultSetMetaData rsmd = rs.getMetaData();
                        int columnsNumber = rsmd.getColumnCount();
                        while (rs.next()) {
                            for (int i = 1; i <= columnsNumber; i++) {
                                if (i > 1)
                                    System.out.print(" ");
                                String columnValue = rs.getString(i);
                                queryoneresult = rs.getString(i);
                            }
                        }

                        if (Integer.valueOf(queryoneresult) == 1) {
                            outputToClient.writeUTF("Username and password have been verified, you can now proceed ");
                        } else {
                            outputToClient
                                    .writeUTF("Your username and/or password are incorrect, access has been denied");
                        }

                    }
                }

            } catch (IOException e) {
                e.printStackTrace();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }
}

Please press one to sign in or two to sign up if you haven't already
1
Please enter your credentials below

Username:
sergio
Password:
Your username and/or password are incorrect, access has been denied

因此，服务器似乎自动获得对密码的响应，并像这样进行，执行也像这样：

Please press one to sign in or two to sign up if you haven't already
1
Please enter your credentials below

Username:
Password:
sergio
Your username and/or password are incorrect, access has been denied

如有任何帮助，不胜感激。

Answer 1

只需将这个scan.next()放在它跳过输入的行上方，字符串password=scan.nextline()；在本例中。

System.out.println(inputFromServer.readUTF());
scan.next();  // Fake input
String password = scan.nextLine();

在服务器端也是：

inputFromClient.readUTF(); // fake input
Password = inputFromClient.readUTF();