带校验和的套接字

import java.io.*;

import java.net.*;/** 时代Java公众号 提 供 **/

public class Sender{

    Socket requestSocket;

    ObjectOutputStream out;

     ObjectInputStream in;

     String message;

    boolean check=true;

    Sender(){}

    

     void run()

    {

        try{

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

            //1. creating a socket to connect to the server

            requestSocket = new Socket("localhost", 2004);

            System.out.println("Connected to localhost in port 2004");

            //2. get Input and Output streams

            out = new ObjectOutputStream(requestSocket.getOutputStream());

            out.flush();//from n o w j a v a . c o m - 时代Java

            in = new ObjectInputStream(requestSocket.getInputStream());

            //3: Communicating with the server

            message = (String)in.readObject();

            System.out.println("server>" + message);

                    

            do{

                try{

                    System.out.println("Enter binary number to send:");

                    message = br.readLine();

                    if(checkbinary(message)){

                        check=false;

                        System.out.println("checksum >"+checksum(message.concat("000")) );

                        message=message.concat(checksum(message.concat("000")));

                        sendMessage(message);

                        }else{

                        System.out.println("Entered data is not in binary format.\n Re" );

                    }

                }

                catch(Exception classNot){

                    System.err.println("data received in unknown format"+classNot);

                }

            }while(check);

            try{

            System.out.println("Data sent" );

            message = (String)in.readObject();

            System.out.println("server>" + message);

            }catch(Exception e){}

                    

        }

        catch(UnknownHostException unknownHost){

            System.err.println("You are trying to connect to an unknown host!");

        }

        catch(IOException ioException){

            ioException.printStackTrace();

        }

        catch(Exception e){}

        finally{

            //4: Closing connection

            try{

                in.close();

                out.close();

                requestSocket.close();

            }

            catch(IOException ioException){

                ioException.printStackTrace();

            }

        }

    }

    boolean checkbinary(String str){

        int n=Integer.valueOf(str);

        int len=str.length();

        int sum=0;

        for(int i=0;i<len;i++){

            sum=n%10;

            if(sum>1) return false;

        }

        return true;

        

    }

    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[