ECHO SERVER

  Echo server is a simple server with only one job to send back whatever is sent to it.

  This post is about creating a simple Echo server on your local machine using JAVA programming language.

STEPS INVOLVED

  

Step 1 : create a socket for the echo server.

Step 2 : take ip address and port number as inputs from the user.

Step 3 : bind the ip address and the port number to the echo server socket created in step 1.

Step 4 : wait for the client's request.

Step 5 : once the client is connected to the echo server, assign it an independent thread for further execution.
[Note : Each client will be assigned a different independent thread]

Step 6 : the work of each thread is to simply send back the information received from the client.

PROGRAM :-

Programs are quite self explanatory as comments are added when and where necessary.

First is the Echo Server program that actually creates the echo server for the clients to connect.

Second is an optional program to connect to Echo Server.
If you are familiar with telnet or similar applications, you can connect to echo server using them and skip the Client program provided.

[Note : Program seems to be in plain text here, I am working on it. Till then copy it to your editor so that keywords are highlighted]
 

1. Echo Server Program 

import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketAddress;
import java.util.Scanner;

public class EchoServer {

    public static void main(String args[]){
   
        try{
   
            // echo server socket
            ServerSocket serverSocket;
   
            // total number of clients
            int clientCount = 0;
       
            // echo server socket address
            SocketAddress serverSocketAddress;
   
            // to obtain input from standard input i.e. keyboard
            Scanner scanner = new Scanner(System.in);
   
            // getting socket address from user  to create echo server socket
            System.out.println("Socket Address :- \n");
           
            System.out.print("\tIP Address :\t");
            String serverIP = scanner.next();
       
            System.out.print("\tPort number :\t");
            short serverPort = Short.parseShort(scanner.next());
       
            serverSocketAddress = new InetSocketAddress(InetAddress.getByName(serverIP), serverPort);
   
            // creation & binding of echo server socket
       
            // echo server socket creation
            serverSocket = new ServerSocket();
       
            // echo server binding
            serverSocket.bind(serverSocketAddress);
       
            if (serverSocket.isBound()){
                System.out.println("Echo Server successfully bound to : " + serverSocketAddress);
            }
            else{
                System.out.println("Echo Server binding unsuccessful");
                System.exit(0);
            }
       
            while (true){
       
                // listening and then accepting client's request to connect
                Socket clientSocket = serverSocket.accept();
               
                if (clientSocket.isConnected()){
                    System.out.println("\nConnected to "+clientSocket.getInetAddress() + '\n');
                    clientCount++;
           
                    // client count as thread name
                    String threadName = Integer.toString(clientCount);
                   
                    Clients client = new Clients(threadName, clientSocket);                   
                }
            }
        }catch(Exception e){
            System.out.println("Exception : " + e.getMessage());
        }
    }
}

class Clients implements Runnable{
   
    // client thread
    private Thread clientThread;
   
    // client socket to communicate
    private Socket clientSocket;
   
    // constructor to initialize the constructor class
    Clients(String clientId,  Socket clientSocket){
       
        // thread name as client id
        clientThread = new Thread(this, clientId);

        this.clientSocket = clientSocket;
       
        // calls the run method
        clientThread.start();
    }
   
    public void run(){
   
        // Scanner object to read data from the standard input
        Scanner scanner = new Scanner(System.in);
   
        // TODO : for the time being only one msg
        try{
            while (true){
               
                // to map the received bytes from client to characters
                InputStreamReader inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
               
                // to store charset mapped received data
                char[] recvData = new char[100];

                // reading data from the input stream
                inputStreamReader.read(recvData, 0, recvData.length);
                System.out.println("Client "+clientThread.getName()+ " : " + new String(recvData));
       
                // sending data to the client
                clientSocket.getOutputStream().write(new String(recvData).getBytes());
            }   
        } catch(Exception e){
                System.out.println("Exception : " + e.getMessage());
        }
    }
}


2. Client Program


import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.Socket;
import java.util.Scanner;

public class Client{
   
    public static void main(String args[]){
   
        // object of Scanner class to handle standard input
        Scanner scanner = new Scanner(System.in);
       
        // server socket to communicate with the server
        Socket serverSocket;
   
        try{
            // getting server socket address from the user to connect
            System.out.println("Server Socket Address :- \n");
           
            System.out.print("\tIP Address :\t");
            String serverIP = scanner.next();
           
            System.out.print("\tPort number :\t");
            short serverPort = Short.parseShort(scanner.next());
           
            // connecting to the specified server
            serverSocket = new Socket(InetAddress.getByName(serverIP), serverPort);
            if (serverSocket.isConnected()){
                System.out.println("\nConnected to "+ serverSocket.getInetAddress() + "\n");
            } else{
                System.out.println("\nConnection FAILED ");
                return;
            }
           
            while (true){
           
                // data to send to the Echo Server
                String dataToSend="";
               
                // to store charset mapped received data
                char[] recvData = new char[100];
               
                // to map the received bytes from the echo server to characters
                InputStreamReader reader = new InputStreamReader(serverSocket.getInputStream());
           
                System.out.print("Me : ");
                // nextLine() must read my input and not the pre existing \n in buffer
                while(dataToSend.length()==0)
                     dataToSend = scanner.nextLine();
           
                // sending data to the server
                serverSocket.getOutputStream().write(dataToSend.getBytes());
           
                // receiving data from the server
                reader.read(recvData, 0, recvData.length);
                System.out.println("Server : " + new String(recvData));
                           
                System.out.println();
            }
        }catch(Exception e){
            System.out.println(e.getMessage());
        }
    }
}

HOW TO RUN THE PROGRAM? 

 

First Echo Server program must be executed

• Compile and run the Echo Server Program.
• Enter the ip address assigned to your PC (type 127.0.0.1 if client program is also executed from the same machine).
• Enter any valid non-reserved port number.
• Echo Server is created. Now the program will wait for the clients to connect.

Once Echo Server is created, execute the client program

• Compile and run the Client Program. 
• Enter the ip address and the port number of the echo server when prompted.
• Now you will be connected to the echo server.
• Whatever you send will be echoed back by the Echo Server.  

OUTPUT 

Output from the client's side :-

Client 1 :

Client 2 :

 Output from the echo server's side :-

This is a basic program which can become a foundation for the advanced program that you are going to make ;)