为什么我的应用程序没有输入 if 语句

我正在尝试用 Java 编写一个控制台客户端-服务器应用程序；使用套接字，我目前有一个简单的登录系统和一个简单的命令系统。登录系统似乎可以正常工作，尽管它会向客户端打印“无效的用户名和密码”行，无论用户是否输入正确的凭据。 - 连接肯定有效。

然而，命令系统似乎根本不起作用，当服务器收到命令时，它似乎没有发回任何东西。

So my 主要问题为什么我的服务器在收到命令时不向客户端发送任何内容？

这是我的服务器：

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

class TCPServer2
{
public static void main(String argv[]) throws Exception
{


    ServerSocket welcomeSocket = new ServerSocket(6789);
    String[][] Login = {{"MATT","UNCP"},{"JOHN","UNCP"},{"CARL","UNCP"}};
    String Command;
    String username;
    String username1;
    String password;
    String password1;
    String cmd;
    while(true)
    {
        Socket connectionSocket = welcomeSocket.accept();
        BufferedReader inFromClient =
           new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
        DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
        username = inFromClient.readLine();
        System.out.println("\nUsername received: " + username);
        password = inFromClient.readLine();
        System.out.println("\nPassword received: " + password);
        username1=username.toUpperCase();
        password1=password.toUpperCase();


        for(int i = 0; i<Login.length; i++)
        {
            if(Login[i][0].equals(username1) && Login[i][1].equals(password1))
            {
                outToClient.writeBytes("Hello " + username1);
                outToClient.writeBytes("\nOther users registered on the server currently include: \n");

                for(int k = 0; k<Login.length; k++)
                {
                    outToClient.writeBytes(Login[k][0]);
                    }
            }
            else {
                outToClient.writeBytes("Invalid Username and/or password.\n");
            }
            }
                        BufferedReader inFromClient2 =
           new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
        DataOutputStream outToClient2 = new DataOutputStream(connectionSocket.getOutputStream());
        Command = inFromClient2.readLine();
        System.out.println("\nCommand received: " + Command);


if(Command.equals("listTranslations"))
{
outToClient2.writeBytes("English,Thai,Geordie,etc.");
}
else
{
if(Command.equals("getCost"))
{
outToClient2.writeBytes("£100\n");
}
else
{
outToClient2.writeBytes("Invalid Command");
}
}

}

    }
}

这是我的客户：

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

class TCPClient2
{
public static void main(String argv[]) throws Exception
{
     String userName;
     String passWord;
     String loginInfo;
     String loginInfo2;
     String loginInfo3;
     String command;
     String commandInfo;
     String commandInfo2;

     BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
     Socket clientSocket = new Socket("localhost", 6789);
     DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
     BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

     System.out.println("Username: ");
     userName = inFromUser.readLine();
     outToServer.writeBytes(userName + "\n");

     System.out.println("Password: ");
     passWord = inFromUser.readLine();
     outToServer.writeBytes(passWord + "\n");

     loginInfo = inFromServer.readLine();
     System.out.println(loginInfo);
     loginInfo2 = inFromServer.readLine();
     System.out.println(loginInfo2);
     loginInfo3 = inFromServer.readLine();
     System.out.println(loginInfo3);

     System.out.println("Please enter a command: ");
     command = inFromUser.readLine();
     outToServer.writeBytes(command);

     commandInfo = inFromServer.readLine();
     System.out.println(commandInfo);
     commandInfo2 = inFromServer.readLine();
     System.out.println(commandInfo);



     clientSocket.close();
 }
}

这是我第一次在 stackoverflow 上问问题，但我过去已经浏览过很多次了。所以我也想对你们提供的优秀社区表示感谢。

我不确定这是否对您有帮助，但检查您是否不必在每次 writeBytes 调用后刷新以真正将数据输出到客户端。

尝试添加 outToClient.flush();