Question

i have created a server and client application which works. however the client or server isn’t working right. if you run the server and run the client on the same machine it works. but if u run the server on 1 machine and run the client on another machine it doesn’t work. if you could help me spot why it isn’t allowing the connection or how to establish connection between the two computers that will be great. thanks you loads. the code is below:

server-----------------------------------------------------------------

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

import javax.swing.*;

public class AdditionalServer extends JFrame {
    private JTextArea textWindow= new JTextArea();
    private int port;

    // the constructor
    public AdditionalServer(int portIn)
    {
        port = portIn;
        setTitle("Addition Sever");
        add("Center",textWindow);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400,300);
        setVisible(true);
        startServer();
    }

    private void startServer() {
        // TODO Auto-generated method stub
        // declare a "general" socket and a server socket
        Socket connection;
        ServerSocket listenSocket;
        //declare low level and high level objects for input
        InputStream inStream;
        DataInputStream inDataStream;

        // declare low level and high level objects for output
        OutputStream outStream;
        DataOutputStream outDataStream;

        // declare other variables
        String client;

        boolean connected;

        while(true){
            try{
                // create a server socket
                listenSocket= new ServerSocket(port,0, InetAddress.getLocalHost());
            //  listenSocket= new ServerSocket(port);
                textWindow.append("Listening on port "+ port +"\n");

                //listen for a connection from the client 
                connection =listenSocket.accept();
                connected = true;

                // create an input stream from the client
                inStream = connection.getInputStream();
                inDataStream = new DataInputStream(inStream);

                // create an output stream from the client
                outStream = connection.getOutputStream();
                outDataStream = new DataOutputStream(outStream);

                // wait for a string from the client
                client = inDataStream.readUTF();
                textWindow.append("Connection esablished with "+ client+ "\n");

                int first, second,sum1;
                String sum = "hi";
                while(connected){
                    //read an integer from the client
                    first = inDataStream.readInt();
                    textWindow.append("First number receievd: "+ first + "\n");

                    //read an integer from the client
                    second = inDataStream.readInt();
                    textWindow.append("Second number receievd: "+ second + "\n");

                    sum1 = first + second;
                    textWindow.append("Sum returned: " + sum1 +"\n");

                    // send the sum to the client 
                    outDataStream.writeInt(sum1);
                    //outDataStream.writeUTF("hi");
                }
            }catch(IOException e){
                connected = false;
            }
        }
    }

    public static void main (String args []){
        new AdditionalServer(8900);

    }
}

client----------------------------------------------------------------------
import java.net.*;
import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class AdditionClient extends JFrame implements ActionListener {

    // declare the visual components

    private JTextField firstNumber = new JTextField(3);
    private JLabel plus = new JLabel("+");
    private JTextField secondNumber = new JTextField(3);
    private JLabel equals = new JLabel("=");
    private JLabel sum= new JLabel();
    private JTextField msg = new JTextField(20);
    private JButton addButton= new JButton("Press to see the sum of the two numbers");

    // declare low level and high level objects for input
    private InputStream inStream;
    private DataInputStream inDataStream;

    // declare low level and high level objects for output
    private OutputStream outStream;
    private DataOutputStream outDataStream;

    // declare socket
    private Socket connection;

    // declare attribute to told details of remote machine and port
    private String remoteMachine;
    private int port;

    // constructor

    public AdditionClient(String remoteMachineIn, int portIn){
        remoteMachine = remoteMachineIn;
        port= portIn;

        //add the visual components
        add(firstNumber);
        add(plus);
        add(secondNumber);
        add(equals);
        add(sum);
        add(msg);
        add(addButton);

        // configure the frame
        setLayout(new FlowLayout());
        setTitle("Addtion Client");
        msg.setHorizontalAlignment(JLabel.CENTER);
        addButton.addActionListener(this);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300,150);
        setVisible(true);

        //start the helper method that starts the client
        startClient();
    }

    private void startClient() {
        // TODO Auto-generated method stub
        try{
            // attempt to create a connection to the server
            connection = new Socket(remoteMachine,port);
            msg.setText("connection establish");

            // create an input stream from the server
            inStream = connection.getInputStream();
            inDataStream = new DataInputStream(inStream);

            //create output stream to the server
            outStream = connection.getOutputStream();
            outDataStream = new DataOutputStream(outStream);

            //send the host IP to the server
            outDataStream.writeUTF(connection.getLocalAddress().getHostAddress());

        }catch (UnknownHostException e){
            msg.setText("Unknow host");
        }
        catch (IOException except){
            msg.setText("Network Exception");
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        try{
            // send the two integers to the server
            outDataStream.writeInt(Integer.parseInt(firstNumber.getText()));
            outDataStream.writeInt(Integer.parseInt(secondNumber.getText()));

            //read and display the results sent back from the server
            //String results= inDataStream.readUTF();
            int results= inDataStream.readInt();
            sum.setText(""+results);
        }catch(IOException ie){
            ie.printStackTrace();
        }
    }

    public static void main (String args[]){
        new AdditionClient("192.168.07", 8900);
    }
}

Answer 1

I think your problem is here.

listenSocket= new ServerSocket(port,0, InetAddress.getLocalHost());

InetAddress.getLocalHost() should be your bind ip. Provide your machine ip here and which should also be visible to your client. I would suggest you to send a ping request from your client machine.

Try to do a ping "your bind ip" to check that your server machine is reachable over the network.

Or try by giving port only.

listenSocket= new ServerSocket(port)