Question

我正在尝试用Java编写控制台客户端 - 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。登录系统似乎有效，但无论用户是否输入正确的凭据，它都会向客户端打印“无效的用户名和密码”行。 - 连接肯定有效。

但是，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内容。

所以我的主要问题是为什么我的服务器在收到命令后不会向客户端发回任何内容？

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();
 }
}

这是我第一次询问有关stackoverflow的问题，但我过去曾经浏览过很多。所以我只是想对你提供的伟大社区说声谢谢。

Answer 1

我不确定这是否会对您有所帮助，但检查在每次writeBytes调用之后您是否不必刷新以真正将数据输出到客户端。

尝试添加outToClient.flush（）;

Answer 2

这是我评论的延续：

我就是这样做的，首先我会用这样的方式替换它：String[][] Login = {{"MATT","UNCP"},{"JOHN","UNCP"},{"CARL","UNCP"}};：

Map<String, String> userDetails = new HashMap<String, String>();
userDetails.put("MAT", "UNCP");
userDetails.put("JOHN","UNCP"); 
userDetails.put("CARL", "UNCP");

然后，而不是这个：

 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");
            }
        }

我会这样做：

if (userDetails.get(username1).equals(password1))
{
    outToClient.writeBytes("Hello " + username1);
                outToClient.writeBytes("\nOther users registered on the server currently include: \n");

    for (String str : userDetails.keySet()
    {
         outToClient.writeBytes(str);
    }

}
else
{
    outToClient.writeBytes("Invalid Username and/or password.\n");
}

我看到它的方式，系统正在工作并打印Invalid credentials字符串是因为，假设您提供这些登录详细信息：CARL和UNCP，您正在通过第二组凭据，因此您的循环将通过将凭证与第一组进行比较来检查凭据，因为它们不匹配，它将打印消息。在第二次迭代中，它将看到凭据匹配并将登录。

有关详细信息，请查看JavaDoc。除了通常的List和Set之外，HashMap是一个通常很容易知道的集合。

为什么我的申请不能进入我的if语句

2 个答案: