Issues with the TCP client-server program

Question

Below is my server program,

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

class TwoWayServer
{
   public static void main(String argv[]) throws Exception
      {
         ServerSocket server_socket = new ServerSocket(1234);

         while(true)
         {
            Socket listen_socket = server_socket.accept();
            BufferedReader client_input = new BufferedReader(new InputStreamReader(listen_socket.getInputStream()));
            DataOutputStream dos = new DataOutputStream(listen_socket.getOutputStream());
            String client_str = client_input.readLine();
            System.out.println(client_str);
            String st=client_str.toUpperCase();
            dos.writeBytes(st);
         }
      }
}

And my client program is as follows,

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

class TwoWayClient
{
 public static void main(String argv[]) throws Exception
 {
  BufferedReader user_input = new BufferedReader( new InputStreamReader(System.in));
  Socket socket = new Socket("localhost", 1234);
  DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
  BufferedReader server_response = new BufferedReader(new InputStreamReader(socket.getInputStream()));
  String client_str = user_input.readLine();
  dos.writeBytes(client_str + '\n');
  String response = server_response.readLine();
  System.out.println("FROM SERVER: " + response);
  socket.close();
 }
}

Here, if I give a string from the clientside then the server return the capitalized form of the string. But the problem is that once I have provided the string, I'm not getting any response from the server. Kindly help.

Answer 1

The problem is in the server in not writing the bytes to the server with a newline character try replacing dos.writeBytes(st);

with

dos.writeBytes(st + "\n");

Answer 2

You may try these modifications to your code.

Server:

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

class TwoWayServer
{
        public static void main(String argv[]) throws Exception
        {
                ServerSocket server_socket = new ServerSocket(1234);

                while(true)
                {
                        Socket listen_socket = server_socket.accept();
                        BufferedReader client_input = new BufferedReader(new InputStreamReader(listen_socket.getInputStream()));
                        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(listen_socket.getOutputStream()));
                        String client_str = client_input.readLine();
                        System.out.println(client_str);
                        String st=client_str.toUpperCase();
                        bw.write(st + '\n');
                        bw.flush();
                }
        }
}

Client:

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

class TwoWayClient
{
        public static void main(String argv[]) throws Exception
        {
                BufferedReader user_input = new BufferedReader( new InputStreamReader(System.in));
                Socket socket = new Socket("localhost", 1234);
                BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                BufferedReader server_response = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String client_str = user_input.readLine();
                bw.write(client_str + '\n');
                bw.flush();
                String response = server_response.readLine();
                System.out.println("FROM SERVER: " + response);
                socket.close();
        }
}