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

public class DJClient { private static InetAddress host; public static void main(String[] args) { try { // Get server IP-address host = InetAddress.getByName(args[0]); } catch(UnknownHostException e){ System.out.println("Host ID not found!"); System.exit(1); } run(Integer.parseInt(args[1])); }

private static void run(int port) { Socket link = null; try{ // Establish a connection to the server link = new Socket(host,port);

// Set up input and output streams for the connection BufferedReader in = new BufferedReader( new InputStreamReader(link.getInputStream())); PrintWriter out = new PrintWriter( link.getOutputStream(),true); //Set up stream for keyboard entry BufferedReader userEntry = new BufferedReader(new InputStreamReader(System.in)); String message, response;

// Get data from the user and send it to the server do{ System.out.print("Enter message: "); message = userEntry.readLine(); out.println(message); }while (!message.equals("DONE"));

// Receive the final report and close the connection response = in.readLine(); System.out.println(response); } catch(IOException e){ e.printStackTrace(); }

finally{ try{ System.out.println(" !!!!! Closing connection... !!!!!"); link.close(); }

catch(IOException e){ System.out.println("Unable to disconnect!"); System.exit(1); }

}

}

}

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

public class DJServer { private static ServerSocket servSock; public static void main(String[] args) { System.out.println("Opening port... "); try{

// Create a server object servSock = new ServerSocket(Integer.parseInt(args[0])); }

catch(IOException e){ System.out.println("Unable to attach to port!"); System.exit(1); }

do { run(); }while (true);

}

private static void run() { Socket link = null; try{

// Put the server into a waiting state link = servSock.accept();

// Set up input and output streams for socket BufferedReader in = new BufferedReader(new InputStreamReader(link.getInputStream())); PrintWriter out = new PrintWriter(link.getOutputStream(),true);

// print local host name String host = InetAddress.getLocalHost().getHostName(); System.out.println("Client has estabished a connection to " + host);

// Receive and process the incoming data int numMessages = 0; String message = in.readLine(); while (!message.equals("DONE")) { System.out.println(message); numMessages ++; message = in.readLine(); }

// Send a report back and close the connection out.println("Server received " + numMessages + " messages"); }

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

finally{ try{ System.out.println("!!!!! Closing connection... !!!!! " + "!!! Waiting for the next connection... !!!"); link.close(); }

catch(IOException e){ System.out.println("Unable to disconnect!"); System.exit(1); } }

}

}

Client-Server code needs client program to accept three optional command line arguments, modify client program to take 3 optional comman line arguments username, server host address and port #. If the user name is not given on the command line, the client programneeds to ask the user for the username . If the server host address is not given on the command line, the client will assume the server is running on the local host. The client program will use a default port which is hard coded if the port number is not given on the command line. Here are the client and server programs that need to be changed