We will see how to communicate between a server and a client using simple network programming using sockets. You can get started with socket programming. Also, a simple client server program might be needed in many situations; you can just copy paste the basic code below and add to it.

We will create a simple server that accepts a client and sends a string message to the client. Client simply prints the message from server in the console.

Basic steps to create a server

1. At the server side, create a server socket with some port number as:
   ServerSocket ss=new ServerSocket(777);
2. Make the server wait till a client accepts connection, using accept() method as:
   Socket s=ss.accept();
3. Get an OutputStream object using getOutputStream() method of Socket class. This stream is used by the socket to send data to the client.
   OutputStream os=s.getOutputStream();
4. Send data to the client using a PrintStream wrapper:
   PrintStream ps=new PrintStream(os);
   ps.println(str);
5. Finally, close the ServerSocket, Socket and PrintStream objects.
   ss.close();
   s.close();
   ps.close();

Basic steps to create a client

1. Create a socket at the client side specifying the server ip addresss and port as:
   Socket s =new Socket(“IPaddress”,port_number);
2. Add InputStream to the Socket to receive data on the InputStream
   InputStream is=s.getInputStream();
3. Read the data from the Socket into the client using BufferedReader wrapper as
   BufferedReader br=new BufferedReader(new InputStreamReader(is));
4. Read data from the BufferedReader using read() or readLine() methods.
   str=br.readLine();
5. Finally, close the BufferedReader and the Socket
   br.close();
   s.close();

Code

Server.java

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

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

        System.out.println("Server");
        ServerSocket ss = new ServerSocket(7777);
        Socket s = ss.accept();
        OutputStream os = s.getOutputStream();
        PrintStream ps = new PrintStream(os);
        ps.println("Hello from server");

        ss.close();
        s.close();
        ps.close();
    }
}
 

Client.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;

public class Client {
    public static void main(String[] args) throws UnknownHostException,
            IOException {
        Socket s = new Socket("mchej01", 7777);
        InputStream is = s.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        System.out.println("message:" + br.readLine());
        br.close();
        s.close();
    }
}

Executing the code

• Compile both classes
• Run the Server first and you can see the server waiting for client.
• Now run the Client and see the message sent from server print in the console.

This is a very simple program, but still let me know if you find any issues or have any doubts,