Message SENDER with CRC - Java Network

Java examples for Network:ServerSocket

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Description

Message SENDER with CRC

Demo Code

///*from  ww  w .  j  a  v a2  s.c o m*/
import java.io.*;
import java.net.*;

public class Reciever
{
     ServerSocket RecieverSocket;
     Socket connection = null;
     ObjectOutputStream out;
     ObjectInputStream in;
     String message,checksum;
     Reciever(){}
     void run()
     {
          try
          {
               BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

               RecieverSocket = new ServerSocket(2004, 10);

               System.out.println("Waiting for connection");
               connection = RecieverSocket.accept();
               senderName = conncetion.getInetAddress().getHostName();
               System.out.println("Connection received from " + senderName);

               out = new ObjectOutputStream(connection.getOutputStream());
               out.flush();
               in = new ObjectInputStream(connection.getInputStream());
               sendMessage("Connection successful ...");

               try
               {
                    message = (String)in.readObject();
                    System.out.println("client>" + message);
                    checksum=checksum(message);
                    message=(checksum.equals("000"))?"correct":"corrupted";
                    sendMessage(message);
               }
               catch(ClassNotFoundException classnot)
               {
                    System.err.println("Data received in unknown format");
               }

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

          finally
          {
               try
               {
                    in.close();
                    out.close();
                    RecieverSocket.close();
               }
               catch(IOException ioException)
               {
                    ioException.printStackTrace();
               }
          }
     }

     String checksum(String str)
     {
          int[] a=new int[20];
          int n=str.length();

          for(int i=0;i<n;i++)
          {
               a[i]=Integer.valueOf(str.substring(i,i+1));
          }
          
          for(int i=0;i<n-3;i++) 
          {
               if(a[i]==1) 
               {
                    a[i]=(a[i]==1)?0:1;
                    a[i+1]=(a[i+1]==1)?1:0;
                    a[i+2]=(a[i+2]==1)?0:1;
                    a[i+3]=(a[i+3]==1)?0:1;
               }
          }

          str=String.valueOf(a[n-3]);
          str=str.concat(String.valueOf(a[n-2]));
          str=str.concat(String.valueOf(a[n-1]));
          return str;
     }

     void sendMessage(String msg)
     {
          try
          {
               out.writeObject(msg);
               out.flush();
               System.out.println("server>" + msg);
          }
          catch(IOException ioException)
          {
               ioException.printStackTrace();
          }
     }

     public static void main(String args[])
     {
          Reciever server = new Reciever();
     
          while(true)
          {
               server.run();
          }
     }
}
// This is just an useless comment!!

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