爲什麼我的應用程序不能輸入if語句

Question

我正在嘗試在Java中編寫控制檯客戶機 - 服務器應用程序;使用套接字，我目前有一個簡單的登錄系統和一個簡單的命令系統。儘管登錄系統將「無效的用戶名和密碼」行打印到客戶端，但無論用戶輸入了正確的憑據，登錄系統似乎都能正常工作。 - 連接絕對有效。

但是，命令系統似乎根本不起作用，當服務器接收到該命令時，它似乎不會發回任何內容。

所以我的主要問題是爲什麼我的服務器收到命令時沒有發回任何東西回客戶端？

這裏是我的服務器：

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"); 
} 
} 

} 

    } 
} 

這裏是我的客戶：

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(); 
} 
} 

這是我第一次問計算器上的一個問題，但我已經瀏覽了很多過去。所以我只想說，感謝你爲你提供的偉大社區。

Answer 1

我不知道這是否會幫助你，但檢查你是否不必在每次writeBytes調用後刷新以真正輸出數據到客戶端。

嘗試添加outToClient.flush（）;

Answer 2

這是我的意見的延續：通過像這樣String[][] Login = {{"MATT","UNCP"},{"JOHN","UNCP"},{"CARL","UNCP"}};：

這是我會怎麼做，首先，我將取代這個

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

然後，而不是這樣的：

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"); 
      } 
     } 

我這樣做：

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，系統正在工作並打印Invalid credentials字符串是因爲，假設您提供了這些日誌詳細信息：CARL和UNCP，您傳遞的是第二組證書，因此您的循環將檢查通過將它們與第一組進行比較並且由於它們不匹配，它將打印該消息。在第二次迭代中，它將看到憑證匹配並將登錄您。

欲瞭解更多信息，請查看JavaDoc。除了通常的List和Set之外，HashMap是一個集合，通常是一件好事。