Question

Using java socket programming rewrite the following program to handle multiple clients simultaneously (multi threaded programming)

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

public class WelcomeClient {
public static void main(String[] args) throws IOException {
  
if (args.length != 2) {
System.err.println(
"Usage: java EchoClient <host name> <port number>");
System.exit(1);
}

String hostName = args[0];
int portNumber = Integer.parseInt(args[1]);

try (
Socket kkSocket = new Socket(hostName, portNumber);
PrintWriter out = new PrintWriter(kkSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(kkSocket.getInputStream()));
) {
BufferedReader stdIn =
new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;

while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Bye."))
break;
  
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}

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

public class WelcomeServer {
public static void main(String[] args) throws IOException {
  
if (args.length != 1) {
System.err.println("Usage: java WelcomeServer <port number>");
System.exit(1);
}

int portNumber = Integer.parseInt(args[0]);

try (
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();   
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
) {
  
String inputLine, outputLine;
  
// Initiate conversation with client
WelcomeProtocol wp = new WelcomeProtocol();
outputLine = wp.processInput(null);
out.println(outputLine);

while ((inputLine = in.readLine()) != null) {
outputLine = wp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye."))
break;
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}

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

public class WelcomeProtocol {
private static final int WAITING = 0;
private static final int SENTWELCOME = 1;
private String str;
private int state = WAITING;
private int currentJoke = 0;

public String processInput(String theInput) {
String theOutput = null;

if (state == WAITING) {
theOutput = "Welcome!";
state = SENTWELCOME;
} else if (state == SENTWELCOME) {
if (theInput.equalsIgnoreCase("bye")) {
   System.exit(1);
   }
   else {
       str = theInput;
           String str2 = str.replaceAll("\\s","");
           int length = str2.length();
           String len = Integer.toString(length);
           theOutput = len;
           state = SENTWELCOME;
   }
}
return theOutput;
}
}

Answer 1

Solution using java:

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

// Server class
public class Server
{

   // Vector to store active clients
   static Vector<ClientHandler> ar = new Vector<>();
  
   // counter for clients
   static int i = 0;

   public static void main(String[] args) throws IOException
   {
       // server is listening on port 1234
       ServerSocket ss = new ServerSocket(1234);
      
       Socket s;
      
       // running infinite loop for getting
       // client request
       while (true)
       {
           // Accept the incoming request
           s = ss.accept();

           System.out.println("New client request received : " + s);
          
           // obtain input and output streams
           DataInputStream dis = new DataInputStream(s.getInputStream());
           DataOutputStream dos = new DataOutputStream(s.getOutputStream());
          
           System.out.println("Creating a new handler for this client...");

           // Create a new handler object for handling this request.
           ClientHandler mtch = new ClientHandler(s,"client " + i, dis, dos);

           // Create a new Thread with this object.
           Thread t = new Thread(mtch);
          
           System.out.println("Adding this client to active client list");

           // add this client to active clients list
           ar.add(mtch);

           // start the thread.
           t.start();

           // increment i for new client.
           // i is used for naming only, and can be replaced
           // by any naming scheme
           i++;

       }
   }
}

// ClientHandler class
class ClientHandler implements Runnable
{
   Scanner scn = new Scanner(System.in);
   private String name;
   final DataInputStream dis;
   final DataOutputStream dos;
   Socket s;
   boolean isloggedin;
  
   // constructor
   public ClientHandler(Socket s, String name,
                           DataInputStream dis, DataOutputStream dos) {
       this.dis = dis;
       this.dos = dos;
       this.name = name;
       this.s = s;
       this.isloggedin=true;
   }

   @Override
   public void run() {

       String received;
       while (true)
       {
           try
           {
               // receive the string
               received = dis.readUTF();
              
               System.out.println(received);
              
               if(received.equals("logout")){
                   this.isloggedin=false;
                   this.s.close();
                   break;
               }
              
               // break the string into message and recipient part
               StringTokenizer st = new StringTokenizer(received, "#");
               String MsgToSend = st.nextToken();
               String recipient = st.nextToken();

               // search for the recipient in the connected devices list.
               // ar is the vector storing client of active users
               for (ClientHandler mc : Server.ar)
               {
                   // if the recipient is found, write on its
                   // output stream
                   if (mc.name.equals(recipient) && mc.isloggedin==true)
                   {
                       mc.dos.writeUTF(this.name+" : "+MsgToSend);
                       break;
                   }
               }
           } catch (IOException e) {
              
               e.printStackTrace();
           }
          
       }
       try
       {
           // closing resources
           this.dis.close();
           this.dos.close();
          
       }catch(IOException e){
           e.printStackTrace();
       }
   }
}