I am trying to have a client and server talk to each other using TCP. The original code ran fine until I modified it to add some more functionality. Now when the Client writes to the Server, Server never seems to get any message.

Here is the output from both the Client and the Server:

Client:Welcome to Cubby! Select from the options below: The options are then listed. The choice is then written to the console for debugging purposes. The program then asks for a username, and the user inputs one. Then the console waits.

Server:Server outputs that it is waiting for a client to connect. Then it displays an acknowledgment when a client does connect. Then it does nothing after that. It is supposed to write to the console the choice that was sent by the client.

#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
{   
}

}

• java
• tcp

As per @asgs's request, I'm posting this as an answer in case someone else stumbles upon this problem:

You should try to flush the output stream after sending something using out.flush().