Basics of Networking

[tabchas]

Hey Guys,

I have two classes: a Server class and Client class. I wrote a simple chat application but it doesn't seem to work. I looked over the code plenty of times but I cant find the problem. Can you guys look over the code?

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

public class Client_Main {
    
    BufferedReader reader;
    PrintWriter writer;
    
    public static void main(String[] args) {
        
        Client_Main main = new Client_Main();
        main.go();
    }

    private void go() {
        
        Scanner scan = new Scanner(System.in);
        System.out.println("Please enter an IP Address: ");
        
        try
        {
            Socket socket = new Socket("192.168.1.105", 4444);
            reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            writer = new PrintWriter(socket.getOutputStream());
        }
        catch (Exception e)
        {
            System.err.println("Failed to connect!");
            System.exit(1);
        }
        
        System.out.println("Network Established!");
        
        Thread readerThread = new Thread(new IncomingReader());
        readerThread.start();
        
        while(true)
        {
            String message = scan.next();
            System.out.println(message);
            writer.print(message);
        }
    }
    
    private class IncomingReader implements Runnable {

        @Override
        public void run() {
            
            String message;
            
            try
            {
                while ((message = reader.readLine()) != null)
                {
                    System.out.println(message);
                    
                }
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
        
        
    }
}

import java.io.*;
import java.net.*;
import java.util.ArrayList;

public class Server_Main {
    
    ArrayList clientOutputStreams;
    
    public static void main(String[] args) {
        
        Server_Main main = new Server_Main();
        main.go();
    }

    private void go() {
        
        clientOutputStreams = new ArrayList();
                
        try 
        {
            ServerSocket serverSocket = new ServerSocket(4444);
            
            while(true)
            {
                Socket clientSocket = serverSocket.accept();
                PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
                clientOutputStreams.add(writer);
                
                Thread t = new Thread(new ClientHandler(clientSocket));
                t.start();
                
                System.out.println("Got Connection!");
            }
        } 
        catch (Exception e) 
        {
            e.printStackTrace();
        }    
    }
        
    private class ClientHandler implements Runnable {
        
        BufferedReader reader;
                
        public ClientHandler(Socket clientSocket) {
            
            try 
            {                
                reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
        
        @Override
        public void run() {
            
            String message;
            
            try
            {               
                while ((message = reader.readLine()) != null)
                {
                    System.out.println("Read: " + message);                    
                }
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }       
    }
}

Thanks!

[JosAH]

As far as I can see your server doesn't send anything back to the client; that means that your IncomingReader object in the client doesn't print anything. Does your server print what it has read from the client?

kind regards,

Jos

[tabchas]

Yes. What I want to happen for now is the client sends a message to the server, and the server prints that message out in console.

This is the server code which reads the message and prints it out to console:

String message;
            
            try
            {               
                while ((message = reader.readLine()) != null)
                {
                    System.out.println("Read: " + message);                    
                }
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }

[JosAH]

You could try a writer.flush() on the client side after it has written some text to the server.

kind regards,

Jos

[Norm]

Try adding a few more debugging statements to see what is happening.
For example use the the InputStream's available() method to see if there are any bytes ready to be read.

[camickr]

For testing I use the localhost IP address to keep it simple:

//Socket socket = new Socket("192.168.1.105", 4444);
Socket socket = new Socket( "127.0.0.1", 4444 );

In addition to the suggestion by JosAH, I found I needed to use the println() method:

//writer.print(message);
writer.println(message);
writer.flush();

[tabchas]

Yea i fixed the problem by using this code:

while(true)
        {
            String message = scan.next();
            System.out.println(message);
            writer.println(message);
            writer.flush();
        }

But I do not get why the code does not work using the Printwriter.print() method? Any ideas? I can probably think of a way that I dont need to use the method but I am curious on the reason that it is not working.

[Norm]

why the code does not work using the Printwriter.print() method?

That part of the code does work. If you leave in the call to the print method and replace the code that reads as follows you will see that the print did work:

/*
                while ((message = reader.readLine()) != null)
                {
                    System.out.println("S read: msg=" + message);                    
                }
*/             
               // Use read() vs readLine() <<<<<<<<<<<<<<<<<<<<<<<<<<<<<
               int c;
               System.out.print("S reading:");
               while((c = reader.read()) != -1)
                  System.out.print((char)c);

[camickr]

But I do not get why the code does not work using the Printwriter.print() method?

Your code is blocking on a readLine() method. So the readLine() method can't complete until it receives a newline string.

[tabchas]

Oh okay. That makes perfect sense.

Thanks for your help everyone!