Java - TCP服務器無法從TCP客戶端讀取

Question

我正在嘗試讓客戶端和服務器使用TCP彼此對話。原代碼運行良好，直到我修改它以添加更多功能。現在，當客戶端寫入服務器時，服務器似乎從未收到任何消息。

下面是從客戶端和服務器的輸出：

客戶：歡迎小房間！ 從以下選項中進行選擇：然後列出選項。 然後將選擇寫入控制檯以進行調試。程序然後要求輸入用戶名，然後用戶輸入一個。然後控制檯等待。

服務器：它正在等待客戶端連接的服務器輸出。然後在客戶端連接時顯示確認。那之後它什麼都不做。它應該向控制檯寫入由客戶端發送的選擇。

#Client# 

import java.math.BigInteger; 
import java.nio.file.Path; 
import java.nio.file.Paths; 
import java.io.*; 
import java.net.*; 
import java.security.*; 
import java.util.*; 
public class Client { 

private static boolean useSockets = true; // Easy for debugging; turns sockets on/off 

public static void main(String[] args) throws Exception { 

    Socket echoSocket = null; // Client to server socket connection object 
    PrintWriter out = null; // Out prints to the socket 
    BufferedReader in = null; // In reads from the socket 
    int portno = 4444;   // The port number of the server we are connecting to 


     //This assumes the server is also run on a local machine 
     InetAddress server_name = InetAddress.getLocalHost(); 

     try { 
      echoSocket = new Socket(server_name, portno); 
     } catch (UnknownHostException e) { 
      System.err.println("Don't know about host."); 
      System.exit(1); 
     } catch (IOException e) { 
      System.err.println("Couldn't get I/O for the connection."); 
      System.exit(1); 
     } 

     //Out will write to the socket and in will read from the socket 
     out = new PrintWriter(echoSocket.getOutputStream()); 
     in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream())); 


    //Read input from the console 
    BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in)); 
    Scanner keyboard = new Scanner(System.in); 
    //At this point we assume that a TCP connection has been made to the server 
    //We now ask the user for a username and password. 
    //If it is the users first time logging in then an account is created. 

    String choice = welcomeMessage(keyboard); 
    System.out.println(choice); 
    if(choice.equals("1")){ 
     out.println(choice); 
     New_Userlogin(in, out, stdIn); 
    } 
    else if (choice.equals("2")){ 
     out.print(choice); 
     Current_Userlogin(in, out, stdIn); 
    } 
    else{ 
     //Exit the program 
    } 




    //User has access to Cubby at this point 

    //Operating System stuff 
    String os = System.getProperty("os.name").toLowerCase(); 
    String path = System.getProperty("user.home"); 

    if (os.indexOf("win") >= 0) { 
     path = path+"\\Cubby"; 
    } else if (os.indexOf("mac") >= 0 || os.indexOf("nix") >= 0 || os.indexOf("nux") >= 0) { 
     path = path+"/Cubby"; 
    } else { 
     System.out.println("Your OS is not supported"); 
    } 

    //Create the Cubby folder if it doesn't exist 
    File f = new File(path); 
    if(!f.exists()){ 
     f.mkdir(); 
    } 

    Path dir = Paths.get(path); 
    WatchDir monitordir = new WatchDir(dir, true); 
    monitordir.processEvents(); 

    // talking with server handled in WatchDir 

    //user requests to quit 
    //sign off from server 

    if (useSockets) 
    { 
     out.close(); 
     in.close(); 
     echoSocket.close(); 
    } 
    stdIn.close(); 
} 

public static String welcomeMessage(Scanner keyboard){ 
    System.out.println("Welcome to Cubby!"); 
    System.out.println("Select from one of the options below: "); 
    String choice = "0"; 
    while((!choice.equals("1")) & (!choice.equals("2")) & (!choice.equals("3"))){ 
     System.out.println("1. Create an account: "); 
     System.out.println("2. Login with an existing account: "); 
     System.out.println("3. Exit: "); 
     choice = keyboard.nextLine(); 
    } 
    return choice; 
} 

public static void New_Userlogin(BufferedReader in, PrintWriter out, BufferedReader stdIn) throws Exception{ 
    while(true){ 
     System.out.println("Please enter a username: "); 
     String username = stdIn.readLine(); 
     out.print(username); 
     int serv_rep = in.read(); 
     if(serv_rep == 0){ 
      System.out.println("Username already taken"); 
     } 
     else{ 
      System.out.println("Account successfully created"); 
      while(true){ 
       System.out.println("Enter a password: "); 
       String password = stdIn.readLine(); 
       System.out.println("Confirm Password: "); 
       String password_check = stdIn.readLine(); 
       if(!password.equals(password_check)){ 
        System.out.println("Passwords did not match. Try again"); 
       } 
       else{ 
        String hashPass = generateHash(password); 
        password = "0000000000000000000"; 
        out.print(hashPass); 
        break; 
       } 
       break; 
      } 
     } 
    } 
} 

public static void Current_Userlogin(BufferedReader in, PrintWriter out, BufferedReader stdIn) throws Exception{ 
    String loginResponse = "invalid"; 

    while (loginResponse != "Good") 
    { 
     System.out.println("Please enter your username: "); 
     String username = stdIn.readLine(); // read in username 

     System.out.println("Please enter your password:"); 
     String password = stdIn.readLine(); 

     // Hash the password 
     String hashPass = generateHash(password); 
     password = "0000000000000000000"; 

     if (useSockets) 
     { 
      // Now we need to send the username and hashedpw to the server for validation 
      out.print(username + "\n" + hashPass); 

      // Now we need to wait for a valid reply from the server 
      loginResponse = in.readLine(); 
     } 

     loginResponse = "Good"; 

     if (loginResponse != "Good") 
     { 
      System.out.println("Invalid username and password"); 
     } 
    } 
} 

private static String generateHash(String password) throws Exception 
{ 
    byte[] hashPass = null; 
    String hashedPassString = null; 

    String saltedpw = "!The$Salt^^~" + password; 

    System.out.println(saltedpw); 

    MessageDigest sha = MessageDigest.getInstance("SHA-256"); 
    hashPass = sha.digest(saltedpw.getBytes("UTF-8")); 

    BigInteger number = new BigInteger(1, hashPass); 
    hashedPassString = number.toString(16); 

    System.out.println(hashedPassString); 

    // For security, Java recommends setting the plaintext pw to all 0s after use 
    saltedpw = "0000000000000000000000000000000000"; 
    password = "0000000000000000000000000000000000"; 

    return hashedPassString; 
} 

} 

#Server# 
import java.net.*; 
import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.PreparedStatement; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 
import java.util.Scanner; 
import java.io.*; 

public class Server { 
//global variable to store the last IP used by the Client 
public static int LAST_IP; 


public static void main(String[] args) throws IOException, ClassNotFoundException, SQLException { 
    checkDir(); 



    //First a socket is created on the given port, 4444 
    ServerSocket serverSocket = null; 
    try { 
     serverSocket = new ServerSocket(4444); 
    } catch (IOException e) { 
     System.err.println("Could not listen on port: 4444"); 
     System.exit(1); 
    } 

    //Then the server does an accept. The server will idle until it 
    //finds a client to accept it. As it stands, this code will only work 
    //for one client at a time. There does exist code out there to allow for 
    //multiple clients if we want to look into that. 
    Socket clientSocket = null; 
    try { 
     System.out.println("Waiting for a client to connect"); 
     clientSocket = serverSocket.accept(); 
    } catch (IOException e) { 
     System.err.println("Accept failed."); 
     System.exit(1); 
    } 
    System.out.println("Server connected to client"); 
    PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true); 
    BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); 

    //The first thing from the client should be a number indicating whether or not 
    //we need to log the user in or create a new account 

    //The first is an int indicating new user or an existing user 
    String choice = null; 
    // if(in.ready()){ 
    Scanner keyboard = new Scanner(clientSocket.getInputStream()); 
    choice = keyboard.next(); 
    System.out.println(choice); 
    //} 

    if(choice.equals("1")){ 
     String username = in.readLine(); 
     createNewUser(username); 
    } 
    // else{ 
    // String username = in.readLine(); 
     //String password = in.readLine(); 
     //if(testCredentials(username, password)){ 
      //out.print("Good"); 
     //} 




    out.close(); 
    in.close(); 
    clientSocket.close(); 
    serverSocket.close(); 
} 

public static void checkDir(){ 
    File f = new File("Users"); 

    //If this is the first time the server is run, there wont be any folder 
    //If the folder exists, then we leave it alone. 
    if(!f.exists()){ 
     f.mkdir(); 
    } 
} 

public static String createNewUser(String name){ 
    //Query the SQL database looking for a username that matches the one a user 
    //has requested. If there is no username, then return 1. If a match was found 
    //return 0; 
    System.out.println("Successfully got to the new User login"); 

    return "0"; 
} 
public static boolean testCredentials(String username, String pass) throws FileNotFoundException, ClassNotFoundException, SQLException 
{ 
} 

} 

Answer 1

按照助理祕書長@的要求，我張貼此作爲對這一問題的情況下，別人跌倒的答案：

你應該嘗試使用out.flush()送點東西后刷新輸出流。