NETWORKING

DICTIONARY CODE
Server CODE:
import java.io.*;
import java.net.*;
import java.util.StringTokenizer;

public class DictServer {
  public static void main(String[] args) throws Exception {
    try{
	  ServerSocket ss =new ServerSocket(8999);
	  Socket s = ss.accept();
	  System.out.println("Successfully connected to client");

	  DataInputStream dis = new DataInputStream(s.getInputStream());
	  DataOutputStream dos = new DataOutputStream(s.getOutputStream());

	  while(true) {
	    String send = "", receive = "";
		//receive = dis.readUTF();

		if((receive = dis.readUTF()) != null) {
		  if(receive == "quit"||receive == "Quit"||receive == "QUIT")
			  break;
		  else {
			System.out.println("Query received: "+receive);
			StringTokenizer st = new StringTokenizer(receive);
			//while(st.hasMoreTokens()) {
				String define = st.nextToken();
				String file = st.nextToken().concat(".txt");
				//System.out.println(file);
				String word = st.nextToken();
			  try {
				File f = new File(file);

				FileInputStream fis = new FileInputStream(f);
				BufferedReader br = new BufferedReader(new InputStreamReader(fis));

				for(String line = br.readLine(); line != null; line = br.readLine()) {
					//System.out.println(line);
					StringTokenizer str = new StringTokenizer(line);
					if(str.nextToken().equals(word)) {
						send = new String(line);
						break;
					}
					line = "";
				}
				//fis.flush();
			  } catch(Exception ex) {
				  System.out.println(ex);
			  }
			//}
			dos.writeUTF(send);
		  }
		}
	  }
	} catch(Exception e){
		System.out.println(e);
	}
  }
}

Client CODE:
import java.io.*;
import java.net.*;

public class DictClient {
  public static void main(String[] args) throws Exception {
	Socket s = new Socket();
    try {
	  SocketAddress address = new InetSocketAddress("127.0.01", 8999);
	  s.connect(address);
	  System.out.println("Successfully connected to server");



	  while(true) {
		  DataInputStream dis = new DataInputStream(s.getInputStream());
	      DataOutputStream dos = new DataOutputStream(s.getOutputStream());
	      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		  String dict, word, send, receive;
		  System.out.println("Enter the dictionary:");
		  dict = br.readLine();
		  if(dict.equals("quit")){
			  dos.writeUTF("quit");
			  break;
		  }
		  System.out.println("Enter the word:");
		  word = br.readLine();
		  send = "DEFINE eng-"+dict+" "+word;
		  System.out.println("Query sent: "+send);
		  dos.writeUTF(send);

		  if((receive = dis.readUTF()) != null)
		    System.out.println(receive);
		  else
			  System.out.println("Word not found.");
	  }

	} catch(Exception e) {
	    System.out.println("This is catch block");
	    System.err.println(e);
	} finally {
		try{
			s.close();
		} catch(Exception e) {
		}
	}
  }
}

1.SSL
import java.io.*;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.*;

public class ServerSSL {
  public static void main(String[] args) throws Exception {
    SSLServerSocket server;
      try {
        SSLServerSocketFactory factory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
        server = (SSLServerSocket) factory.createServerSocket(8999);
        SSLSocket client  = (SSLSocket) server.accept();
        System.out.println("Securely connected to client...");


        DataInputStream dis = new DataInputStream(client.getInputStream());
        DataOutputStream dos = new DataOutputStream(client.getOutputStream());

        /*String[] cipher = server.getEnabledCipherSuites();
		/*int len = cipher.length;
        dos.writeUTF(String.valueOf(len));*/

		String[] supported = client.getSupportedCipherSuites();
		//dos.writeUTF(cipher[5]);
	    client.setEnabledCipherSuites(supported);


        String receive = "";
        if((receive = dis.readUTF()) != null)
          System.out.println("Received: "+receive);

        dos.writeUTF(receive);

        server.close();
      } catch(Exception ex) {
          System.err.println(ex);
      }
  }
}
--------------------------------------------------------------------------------------------------------------
import javax.net.ssl.*;
import java.io.*;

public class ClientSSL {
  public static void main(String[] args) throws Exception {
    try {
      SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault();
      SSLSocket client = (SSLSocket) factory.createSocket("127.0.0.1", 8999);
      System.out.println("Securely connected to server...");

      DataInputStream dis = new DataInputStream(client.getInputStream());
      DataOutputStream dos = new DataOutputStream(client.getOutputStream());
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

      /*String length = dis.readUTF();
      int l = Integer.parseInt(length);
      String[] s = new String[l];
      for(int i = 0; i < l; i++)
        s[i] = dis.readUTF();*/

	  String[] supported = client.getSupportedCipherSuites();
      client.setEnabledCipherSuites(supported);
	  /*String cipher = dis.readUTF();
	  String[] selCipher = {"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256"};
	  client.setEnabledCipherSuites(selCipher);*/

      String send, receive = "";
      send = br.readLine();
      dos.writeUTF(send);
	  System.out.println("Sent : "+send);

      if((receive = dis.readUTF()) != null)
        System.out.println("Received : "+receive);
    } catch(Exception ex) {
        System.err.println(ex);
    }
  }
}

2	The message entered in the client is sent to the server and the server encodes the message and returns it to the client. Encoding is done by replacing a character by the character next to it i.e. a as b, b as c …z as a. This process is done using UDP. Write a program for the above


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

class Server {
public static void main(String args[]) throws Exception
{
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[5];
byte[] sendData = new byte[5];
while(true)
{

DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
String sentence = new String(receivePacket.getData());

char c[]=sentence.toCharArray();
int n=c.length;
int i;
char zu;
String str="";

for(i=0;i<n;i++)
{
if(c[i]=='z')
{
zu='a';
}
else{
int num=(int)c[i];
num++;
zu=(char)num;
}
str=str+zu;

}

sendData = str.getBytes();


InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();

DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
serverSocket.send(sendPacket);
}
}
}
--------------------------------------------------------------------------------------------
import java.io.*;
import java.net.*;

class Client {
public static void main(String args[]) throws Exception
{
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
DatagramSocket clientSocket = new DatagramSocket();
InetAddress IPAddress = InetAddress.getByName("localhost");
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[1024];
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
clientSocket.receive(receivePacket);
String modifiedSentence =
new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}

1.	3. Display the result of the following  DatagramPacket’s getter methods
a.	public InetAddress getAddress()
b.	public int getPort()
c.	public SocketAddress getSocketAddress()
d.	public byte[] getData()
e.	public int getLength()
f.	public int getOffset()

import java.io.*;

import java.net.*;

class UDPServer {

public static void main(String args[]) throws Exception{

DatagramSocket serverSocket = new DatagramSocket(9876);//create socket wd only port no

int i;

char c,cc;

byte[] receiveData = new byte[1024];//data to be sent back

while(true){

DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);//datagram packet created to receive data

serverSocket.receive(receivePacket);//we receive the packet from client in the dp object

String sentence = new String(receivePacket.getData());//we extract the data out of the packet and convert to string

System.out.println("RECEIVED: " + sentence);//print the recieved data as string

System.out.println("This packet is addressed to "+ receivePacket.getAddress() + " on port " + receivePacket.getPort());

System.out.println("There are " + receivePacket.getLength()

+ " bytes of data in the packet");

System.out.println(new String(receivePacket.getData(), "UTF-8"));

System.out.println(receivePacket.getOffset());

System.out.println(receivePacket.getLength());

System.out.println(receivePacket.getSocketAddress());

}

}

}
-----------------------------------------------------------------------------------
import java.io.*;

import java.net.*;

class UDPClient {

public static void main(String args[]) throws Exception    {

BufferedReader inFromUser =new BufferedReader(new InputStreamReader(System.in));

DatagramSocket clientSocket = new DatagramSocket();//for client socket we don't need port no ..to create server socket we need port no.

InetAddress IPAddress = InetAddress.getByName("localhost");

byte[] sendData = new byte[1024];

String sentence = inFromUser.readLine();

sendData = sentence.getBytes();

DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);

clientSocket.send(sendPacket);

   }

 }

1.	4. Implement a UDP program that  send the same datagram to many different recipients (Use set methods)

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

public class MultiSend {
  public static void main(String[] args) {
	try {
    String s = "Really important message";
	byte[] data = s.getBytes();
	DatagramPacket dp = new DatagramPacket(data, data.length);
	dp.setPort(2000);
	DatagramSocket socket = new DatagramSocket();
	String network = "128.238.5.";
	for(int host = 1; host < 255; host++) {
	  try {
	    InetAddress remote = InetAddress.getByName(network + host);
		dp.setAddress(remote);
		socket.send(dp);
		System.out.println("Sent to address : "+ network + host);
	  } catch(Exception e) {
	    //skip it, continue with next host
	  }
	}
	} catch(Exception ex) {
		System.err.println(ex);
	}
  }
}


1.Write a program that displays the content of a web page using URLConnection class.
import java.io.*;
import java.net.*;
public class urlques
{
public static void main(String args[])
{
if(args.length>0)
{
try{
	URL u= new URL(args[0]);
	URLConnection uc = u.openConnection();
	try {
		InputStream raw = uc.getInputStream();  // autoclose
	InputStream buffer = new BufferedInputStream(raw);
	Reader reader = new InputStreamReader(buffer);
	int c;
	while ((c = reader.read()) != -1) {
		System.out.print((char) c);
	}
	}

 catch (MalformedURLException ex) {
	System.err.println(args[0] + " is not a parseable URL");
}
}
catch (IOException ex) {
	System.err.println(ex); }
	 }
	  }
	   }



1. Display the details of HTTP Response header fields.
a. Using Specific header fields
import java.io.*;
import java.net.*;
import java.util.Date;
public class urlques
{
public static void main(String args[])
{
if(args.length>0)
{
try{
	URL u= new URL(args[0]);
	URLConnection uc = u.openConnection();

	System.out.println("type of content:"+uc.getContentType());
	System.out.println("content Length:"+uc.getContentLength());
	System.out.println("content encoding:"+uc.getContentEncoding());
	Date documentSent = new Date(uc.getDate());
	String date= documentSent.toString();
	System.out.println("Date:"+date);
	Date documentModify = new Date(uc.getLastModified());
	String modify= documentSent.toString();
	System.out.println("ModifyDate:"+modify);
	Date docexpire = new Date(uc.getExpiration());
	String expire= docexpire.toString();
	System.out.println("ExpirationDate:"+expire);

}
catch (IOException ex) {
	System.err.println(ex); }
	 }
	  }
	   }

b. Using Arbitrary header fields
import java.io.*;
import java.net.*;
import java.util.Date;
public class urlques
{
public static void main(String args[])
{
if(args.length>0)
{
try{
	URL u= new URL(args[0]);
	URLConnection uc = u.openConnection();

	String contentType = uc.getHeaderField("content-type");
	String header6 = uc.getHeaderFieldKey(6);
	String header = uc.getHeaderField(3);
	System.out.println("content-type:"+contentType);
	System.out.println("Header-field-key:"+header6);
	System.out.println("Header-field:"+header);

}
catch (IOException ex) {
	System.err.println(ex); }
	 }
	  }
	   }
2. Implement a program that Configure the Client Request HTTP Header by using setRequestProperty method. Also display the updated request header values using getRequestProperty.
import java.io.*;
import java.net.*;
import java.util.Date;
public class urlques
{
public static void main(String args[])
{
if(args.length>0)
{
try{
	URL u= new URL(args[0]);
	URLConnection uc = u.openConnection();

	uc.setRequestProperty("Cookie","username=elharo; password=ACD0X9F23JJJn6G; session=100678945");
	String a= uc.getRequestProperty("Cookie");
	System.out.println(a);
}
catch (IOException ex) {
	System.err.println(ex); }
	 }
	  }
	   }







Develop a TCP client/server application for transferring a text file from client to server.

//Server

import java.io.*;

import java.net.*;


class TCPServer {

    public static void main(String args[]) throws Exception {

        int firsttime = 1;

        while (true) {

            String clientSentence;

            String capitalizedSentence="";

            ServerSocket welcomeSocket = new ServerSocket(3248);

            Socket connectionSocket = welcomeSocket.accept();

            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));

            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

            clientSentence = inFromClient.readLine();

            //System.out.println(clientSentence);

            if (clientSentence.equals("set")) {

                outToClient.writeBytes("connection is ");

                System.out.println("running here");

                //welcomeSocket.close();

                //outToClient.writeBytes(capitalizedSentence);

            }

            capitalizedSentence = clientSentence.toUpperCase() + "\n";

            //if(!clientSentence.equals("quit"))

            outToClient.writeBytes(capitalizedSentence+"enter the message or command: ");

            System.out.println("passed");

            //outToClient.writeBytes("enter the message or command: ");

            welcomeSocket.close();

            System.out.println("connection terminated");

        }

    }

}


//Client

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


class TCPClient {

 public static void main(String args[]) throws Exception {

        String sentence;

        String modifiedSentence;

        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));

        Socket clientSocket = new Socket("127.0.0.1", 6789);

        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());

        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        sentence = inFromUser.readLine();

        outToServer.writeBytes(sentence + "\n");

        modifiedSentence = inFromServer.readLine();

        System.out.println("FROM SERVER:" + modifiedSentence);

        clientSocket.close();

    }

}


Implement a TCP based server program to authenticate the client’s User Name and Password. The validity of the client must be sent as the reply message to the client and display it on the standard output.

	//Client

	import java.io.*;
	import java.net.*;
	class TCPClientAuth {

   	 public static void main(String argv[]) throws Exception
    	{
       String username;
       String password;
	String auth;

        BufferedReader inFromUser =
          new BufferedReader(new InputStreamReader(System.in));

        Socket clientSocket = new Socket("localhost", 6789);

        DataOutputStream outToServer =
          new DataOutputStream(clientSocket.getOutputStream());

                BufferedReader inFromServer =
          new BufferedReader(new
          InputStreamReader(clientSocket.getInputStream()));

	System.out.print("Username :");
        username = inFromUser.readLine();

	System.out.print("Password :");
	password = inFromUser.readLine();


        outToServer.writeBytes(username + '\n' + password + '\n' );

        auth = inFromServer.readLine();

        System.out.println("FROM SERVER: " + auth);

        clientSocket.close();

    }
}

//Server

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

class TCPServerAuth {

  public static void main(String argv[]) throws Exception
    {
      String username;
      String password;
      String auth;

      ServerSocket welcomeSocket = new ServerSocket(6789);

      while(true) {

            Socket connectionSocket = welcomeSocket.accept();

           BufferedReader inFromClient =
              new BufferedReader(new
              InputStreamReader(connectionSocket.getInputStream()));



           DataOutputStream  outToClient =
             new DataOutputStream(connectionSocket.getOutputStream());

           username = inFromClient.readLine();
	   password = inFromClient.readLine();


           if (username.equals("Admin")){
		if (password.equals("root")){
			auth = "Login Successful!";
		}else{
			auth = "Wrong Password";
		}
	   }else{
		auth = "Wrong Username";
	   }

           outToClient.writeBytes(auth);
	   connectionSocket.close();
        }
    }
}

Q2) Implement echo server and client in java using TCP sockets.

//Server

import java.io.*;

import java.net.*;


public class EchoServer

{

public static void main(String args[]) throws Exception

{

try

{

int Port;

BufferedReader Buf =new BufferedReader(new

InputStreamReader(System.in));

System.out.print(" Enter the Port Address : " );

Port=Integer.parseInt(Buf.readLine());

ServerSocket sok =new ServerSocket(Port);

System.out.println(" Server is Ready To Receive a Message. ");

System.out.println(" Waiting ..... ");

Socket so=sok.accept();

if(so.isConnected()==true)

            System.out.println(" Client Socket is Connected Succecfully. ");

InputStream in=so.getInputStream();

OutputStream ou=so.getOutputStream();

PrintWriter pr=new PrintWriter(ou);

BufferedReader buf=new BufferedReader(new

InputStreamReader(in));

String str=buf.readLine();

System.out.println(" Message Received From Client : " + str);

System.out.println(" This Message is Forwarded To Client. ");

pr.println(str);

pr.flush();

}

 catch(Exception e)

  {

  System.out.println(" Error : " + e.getMessage());

  }

}

}




//Client

import java.io.*;

import java.net.*;


public class EchoClient

{

public static void main(String args[]) throws Exception

{

try {

int Port;

BufferedReader Buf =new BufferedReader(new

InputStreamReader(System.in));

System.out.print(" Enter the Port Address : " );

Port=Integer.parseInt(Buf.readLine());

Socket sok=new Socket("localhost",Port);

if(sok.isConnected()==true)

            System.out.println(" Server Socket is Connected Succecfully. ");

InputStream in=sok.getInputStream();

OutputStream ou=sok.getOutputStream();

PrintWriter pr=new PrintWriter(ou);

BufferedReader buf1=new BufferedReader(new

InputStreamReader(System.in));

BufferedReader buf2=new BufferedReader(new

InputStreamReader(in));

String str1,str2;

System.out.print(" Enter the Message : ");

str1=buf1.readLine();

pr.println(str1);

pr.flush();

System.out.println(" Message Send Successfully. ");

str2=buf2.readLine();

System.out.println(" Message From Server : " + str2);

     }

  catch(Exception e)

  {

   System.out.println(" Error : " + e.getMessage());

  }

}

}


Q3) Implement date server and client in java using TCP sockets.

//Server


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


class DateServer

{

    public static void main(String args[]) throws Exception

    {

        ServerSocket s=new ServerSocket(5217);


        while(true)

        {

            System.out.println("Waiting For Connection ...");

            Socket soc=s.accept();

            DataOutputStream out=new DataOutputStream(soc.getOutputStream());

            out.writeBytes("Server Date" + (new Date()).toString() + "\n");

            out.close();

            soc.close();

        }

    }

}



//Client

import java.io.*;

import java.net.*;



class DateClient

{

    public static void main(String args[]) throws Exception

    {

        Socket soc=new Socket(InetAddress.getLocalHost(),5217);

        BufferedReader in=new BufferedReader(

                new InputStreamReader(

                        soc.getInputStream()

                        )

                    );



        System.out.println(in.readLine());

    }

}

Q4) Write a program to implement a simple message transfer from client to server process using TCP/IP.

//Server

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class tcpServer

{

    private static Socket socket;

    public static void main(String[] args)

    {

        try

        {

            int port = 25000;

            ServerSocket serverSocket = new ServerSocket(port);

            System.out.println("Server Started and listening to the port 25000");


            //Server is running always. This is done using this while(true) loop

            while(true)

            {

                //Reading the message from the client

                socket = serverSocket.accept();

                InputStream is = socket.getInputStream();

                InputStreamReader isr = new InputStreamReader(is);

                BufferedReader br = new BufferedReader(isr);

                String number = br.readLine();

                System.out.println("Message received from client is "+number);


                //Multiplying the number by 2 and forming the return message

                String returnMessage;

                try

                {

                    int numberInIntFormat = Integer.parseInt(number);

                    int returnValue = numberInIntFormat*2;

                    returnMessage = String.valueOf(returnValue) + "\n";

                }

                catch(NumberFormatException e)

                {

                    //Input was not a number. Sending proper message back to client.

                    returnMessage = "Please send a proper number\n";

                }



                //Sending the response back to the client.

                OutputStream os = socket.getOutputStream();

                OutputStreamWriter osw = new OutputStreamWriter(os);

                BufferedWriter bw = new BufferedWriter(osw);

                bw.write(returnMessage);

                System.out.println("Message sent to the client is "+returnMessage);

                bw.flush();

            }

        }

        catch (Exception e)

        {

            e.printStackTrace();

        }

        finally

        {

            try

            {

                socket.close();

            }

            catch(Exception e){}

        }

    }

}



//Client

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.InetAddress;
import java.net.Socket;

public class tcpClient

{


    private static Socket socket;


    public static void main(String args[])

    {

        try

        {

            String host = "localhost";

            int port = 25000;

            InetAddress address = InetAddress.getByName(host);

            socket = new Socket(address, port);


            //Send the message to the server

            OutputStream os = socket.getOutputStream();

            OutputStreamWriter osw = new OutputStreamWriter(os);

            BufferedWriter bw = new BufferedWriter(osw);


            String number = "2";

            String sendMessage = number + "\n";

            bw.write(sendMessage);

            bw.flush();

            System.out.println("Message sent to the server : "+sendMessage);


            //Get the return message from the server

            InputStream is = socket.getInputStream();

            InputStreamReader isr = new InputStreamReader(is);

            BufferedReader br = new BufferedReader(isr);

            String message = br.readLine();

            System.out.println("Message received from the server : " +message);

        }

        catch (Exception exception)

        {

            exception.printStackTrace();

        }

        finally

        {

            //Closing the socket

            try

            {

                socket.close();

            }

            catch(Exception e)

            {

                e.printStackTrace();

            }

        }

    }

}

Implement echo server and client in java using UDP sockets
udp_client_echo.java
import java.io.*;
import java.net.*;

public class udp_client_echo
{
    public static void main(String args[])
    {
        DatagramSocket sock = null;
        int port = 7777;
        String s;

        BufferedReader cin = new BufferedReader(new InputStreamReader(System.in));

        try
        {
            sock = new DatagramSocket();

            InetAddress host = InetAddress.getByName("localhost");

            while(true)
            {
                echo("Enter message to send : ");
                s = (String)cin.readLine();
                byte[] b = s.getBytes();

                DatagramPacket  dp = new DatagramPacket(b , b.length , host , port);
                sock.send(dp);
                byte[] buffer = new byte[65536];
                DatagramPacket reply = new DatagramPacket(buffer, buffer.length);
                sock.receive(reply);

                byte[] data = reply.getData();
                s = new String(data, 0, reply.getLength());

                echo(reply.getAddress().getHostAddress() + " : " + reply.getPort() + " - " + s);
            }
        }

        catch(IOException e)
        {
            System.err.println("IOException " + e);
        }
    }
    public static void echo(String msg)
    {
        System.out.println(msg);
    }
}

udp_server.java

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

public class udp_server_echo
{
    public static void main(String args[])
    {
        DatagramSocket sock = null;

        try
        {
            sock = new DatagramSocket(7777);
            byte[] buffer = new byte[65536];
            DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);
            echo("Server socket created. Waiting for incoming data...");
            while(true)
            {
                sock.receive(incoming);
                byte[] data = incoming.getData();
                String s = new String(data, 0, incoming.getLength());

                echo(incoming.getAddress().getHostAddress() + " : " + incoming.getPort() + " - " + s);

                s = "OK : " + s;
                DatagramPacket dp = new DatagramPacket(s.getBytes() , s.getBytes().length , incoming.getAddress() , incoming.getPort());
                sock.send(dp);
            }
        }

        catch(IOException e)
        {
            System.err.println("IOException " + e);
        }
    }

    public static void echo(String msg)
    {
        System.out.println(msg);
    }
}



Q3. Implement a chat server and client in java using UDP sockets.
UdpClientChat.java
import java.io.*;
import java.util.*;
import java.net.*;

class UdpClientChat
{
public static void main(String args[])
{
try
{
while(true)
{
DatagramSocket clientSocket=new DatagramSocket();
byte[] sendData=new byte[1024];
byte[] receiveData=new byte[1024];
System.out.println("Client:");
BufferedReader inFromClient=new BufferedReader(new InputStreamReader(System.in));
String s=inFromClient.readLine();
sendData=s.getBytes();
InetAddress Ip=InetAddress.getByName("localhost");
DatagramPacket sendPacket=new DatagramPacket(sendData,sendData.length,Ip,7777);
clientSocket.send(sendPacket);
System.out.println("\n");
DatagramPacket receivePacket=new DatagramPacket(receiveData,receiveData.length);
clientSocket.receive(receivePacket);
String r=new String(receivePacket.getData());
System.out.println("Server:"+r+"\n");
}
}catch(Exception e)
{
System.out.println(e);
}
}
}

UdpServerChat.java
import java.io.*;
import java.util.*;
import java.net.*;
class UdpServerChat
{
	public static void main(String args[])
	{
		try{
		while(true)
		{
			DatagramSocket serverSocket= new DatagramSocket(7777);
			byte[] sendData=new byte[1024];
			byte[] recieveData=new byte[1024];
			DatagramPacket recievePacket=new DatagramPacket(recieveData,recieveData.length);
			serverSocket.receive(recievePacket);
			String r=new String(recievePacket.getData());
			System.out.println("Client:"+r+"\n");

			BufferedReader outToClient=new BufferedReader(new InputStreamReader(System.in));
			System.out.println("Server:");
			String s=outToClient.readLine();
			System.out.println("\n");
			sendData=s.getBytes();
			InetAddress Ip=recievePacket.getAddress();
			int port=recievePacket.getPort();
			DatagramPacket sendPacket=new DatagramPacket(sendData,sendData.length,Ip,port);
			serverSocket.send(sendPacket);
			serverSocket.close();
		}
		}catch(Exception e)
		{
			System.out.println(e);
		}
	}
}


QUES) REVERSE A STRING

import java.util.*;

class ReverseString
{
   public static void main(String args[])
   {
      String original, reverse = "";
      Scanner in = new Scanner(System.in);

      System.out.println("Enter a string to reverse");
      original = in.nextLine();

      int length = original.length();

      for ( int i = length - 1 ; i >= 0 ; i-- )
         reverse = reverse + original.charAt(i);

      System.out.println("Reverse of entered string is: "+reverse);
   }
}

QUES)REVERSE A NUMBER
import java.util.Scanner;

class ReverseNumber
{
   public static void main(String args[])
   {
      int n, reverse = 0;

      System.out.println("Enter the number to reverse");
      Scanner in = new Scanner(System.in);
      n = in.nextInt();

      while( n != 0 )
      {
          reverse = reverse * 10;
          reverse = reverse + n%10;
          n = n/10;
      }

      System.out.println("Reverse of entered number is "+reverse);
   }
}