How to use Socket API for creating Client-Server application in Java

In this example we make use of ServerSocketChannel and SocketChannel to create a simple Echo application where in the Server would print the data sent by the client.

also read:

• Java Tutorials
• Java EE Tutorials
• Design Patterns Tutorials
• Java File IO Tutorials

The code is explained with the required comments:

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Scanner;

/**
 * This creates a server on a particular IP address and the port.
 *
 */
public class ServerClass {

  public static void main(String[] args) {

    // Create a Server socket channel.
    try (ServerSocketChannel serverSocket = ServerSocketChannel.open()) {

      // Bind the server socket channel to the IP address and Port
      serverSocket.bind(new InetSocketAddress("127.0.0.1", 6667));
      System.out.println("Waiting for client connections");

      while (true) {
        
        //Wait and Accept the client socket connection. 
        try (SocketChannel socketChannel = serverSocket.accept()) {
          
          //Printing the address of the client.
          System.out.println("Obtained connection from: "+socketChannel.getRemoteAddress().toString());
          
          //Creating a reader for reading the content on the socket input stream.
          Scanner socketReader = new Scanner(socketChannel.socket().getInputStream());
          while(socketReader.hasNext()){
            
            //Reading the content of the socket input stream.
            System.out.println(socketReader.nextLine());
            
          }

        } catch(IOException ex){
          ex.printStackTrace();
        }
      }

    } catch (IOException ex) {
      ex.printStackTrace();
    }
  }

}

and the client which connects to the server is:

import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetSocketAddress;
import java.nio.channels.SocketChannel;

public class CilentClass {
  
  public static void main(String[] args) {
    
    //Create a client socket.
    try(SocketChannel socketChannel = SocketChannel.open()){
      
      //Bind the client socket to the server socket.
      socketChannel.connect(new InetSocketAddress("127.0.0.1", 6667));
      
      //Writing to the socket channel.
      PrintWriter writer = new PrintWriter(socketChannel.socket().getOutputStream(), true);
      writer.println("Client sending instruction 1");
      writer.println("Client sending instruction 2");
      writer.println("Client sending instruction 3");
      writer.println("Client sending instruction 4");
      
    }catch(IOException ex){
      ex.printStackTrace();
    }
    
  }
}