Question

I’m new to Java Computer Networking and not so great at programming in the first place, however, I was able to construct this Server and Client that is supposed to accept a just one line. A function (add, sub, divide) and two ints and then compute and print the answer. I’m able to connect the two, but when I type the line in it does nothing. Any insight would be appreciated. Thank you!

Server

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;
import java.lang.Math;


public class MathServer
{


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

     ServerSocket yourSock = new ServerSocket(50000);
     System.out.println("Please Wait....");

     while(true)
     {
        Socket clientSock = yourSock.accept();
        System.out.println("Connected!");
        process(clientSock);


     }


  }

  static void process(Socket sock) throws IOException
  {
     InputStream in = sock.getInputStream();
     BufferedReader br = new BufferedReader(new InputStreamReader(in));

     OutputStream out = sock.getOutputStream();
     PrintWriter pw = new PrintWriter(out,true);

  //Talk to the client
     String input = br.readLine();

     while(input != null && !input.equals("disconnect"))
     {  

        Scanner sc = new Scanner(System.in);
        String func = sc.nextLine();
        double num1 = sc.nextInt();
        double num2 = sc.nextInt();

        double answer;          

        switch (func)
        {
           case "add":  answer = num1 + num2;
              System.out.println(answer);
              break;

           case "sub":  answer = num1 - num2;
              pw.println(answer); 
              break;

           case "multiply":  answer = num1 * num2;
              pw.println(answer);        
              break;

           case "power":  answer = Math.pow(num1, num2);
              pw.println(answer);
              break;

           case "divide":  answer = num1 / num2;
              pw.println(answer);         
              break;

           case "remainder": answer = num1 % num2;
              pw.println(answer);       
              break;

           case "square": answer = Math.sqrt(num1) ;
              pw.println(answer);       
              break;

           case "cube": answer= Math.cbrt(num1);
              pw.println(answer);        
              break;



        }

        sock.close();
     }

  }
}

Client

import java.io.*;
import java.net.Socket;
import java.util.Scanner;


public class Client
{


  public static void main(String[] args) throws Exception
  {
     Socket Sock = new Socket("localhost", 50000);
     BufferedReader br = new BufferedReader(new InputStreamReader(Sock.getInputStream()));
     PrintWriter pw = new PrintWriter(Sock.getOutputStream(), true);


     Scanner sc = new Scanner(System.in);
     String input;


     while(true)
     {
     //System.out.println("Please enter your function and numbers:");
        input = sc.nextLine();

        pw.println(input);

        if(input.equals("disconnect"))
        {
           System.out.println("You have been disconnected");
           break;

        }


        System.out.println(br.readLine());
     }

     Sock.close();

  }


}

Answer 1

• You need to arrange the order that you send and receive data between your client & server.
• As mentioned by @Jacob, you are reading from System.in instead of your input data, you could read from the input String.
• Place the readLine statement within your while statemet to continue to read from the client.

This would look like:

String input;
while ((input = br.readLine())!= null && !input.equals("disconnect")) {
   Scanner sc = new Scanner(input);
   String func = sc.next();
   double num1 = sc.nextDouble();
   double num2 = sc.nextDouble();
   ...
}

Next, move your sock.close() statement outside of your while loop.

Now, your input commands from the client will appear on a single line, e.g.

add 12 15

Also flush the data from your client:

pw.flush();