通过Java中的套接字连接接收数据时无法写入文件

Question

I tried to implement a send-receive example via a socket but It didn't work well. The sender sends the data successfully and the Receiver receives the data and shown in the console but I want to save this data in a file and I couldn't. As I noticed that the receiver keeps listeninig without ending the while loop. So can anyone help me to solve this problem ?

The Sender module

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


public class UDPSend {


 public static void main(String[] args) throws IOException
  {
      FileInputStream fstream = new FileInputStream("T.txt");
      DataInputStream in = new DataInputStream(fstream);
      BufferedReader br = new BufferedReader(new InputStreamReader(in));

      File file = new File("T.txt");
      FileInputStream fis = new FileInputStream(file);
      byte[] fsize = new byte[(int) file.length()];
      int size = fis.read(fsize);
                System.out.println("Size = " + size);



      InetAddress addr = InetAddress.getByName("localhost");
      byte[]  buf  = new byte[10000];

      String DataLine; 
      while ((DataLine = br.readLine()) != null)  
      { 
                DatagramPacket packet =new DatagramPacket(DataLine.getBytes(),         DataLine.length() , addr, 4555);
          System.out.println (DataLine);
          DatagramSocket socket = new DatagramSocket();
          socket.send(packet);

      }//end while loop


  }//end main method 

 }

The Receiver module

import java.io.*;
import java.net.*;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class UDPRecieve {



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

      FileWriter fw = new FileWriter(new File("D:/JavaPrograms/Multimedia-proj-2/src/outtt.txt"));
      fw.write("hi");
      try{
      //DatagramSocket serverSocket = new DatagramSocket(4555);
      DatagramSocket Socket = new DatagramSocket(4555);
      byte[] receiveData = new byte[1000000];    
     // byte[] sendData = new byte[1024];
      //while(true)
      while(receiveData !=null)
         {  
            DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
            Socket.receive(receivePacket);
            String sentence = new String( receivePacket.getData());
            fw.write(sentence);
            fw.flush();
            System.out.printf("RECEIVED: %s " , new String(receivePacket.getData()));
            //System.out.println("Done");
            //InetAddress IPAddress = receivePacket.getAddress();
            //int port = receivePacket.getPort();
            //String capitalizedSentence = sentence.toUpperCase();
           /* sendData = capitalizedSentence.getBytes();
            DatagramPacket sendPacket =
            new DatagramPacket(sendData, sendData.length, IPAddress, port);
            serverSocket.send(sendPacket);*/
         }


      fw.flush();
      fw.close(); 

      } catch (Exception e) {
          System.err.println(e);
        }

    }
}

Thanks in advance.

Answer 1

You can achive it by following code changes.In Receiver class make changes in following loop.

while (receiveData != null) {
                DatagramPacket receivePacket = new DatagramPacket(receiveData,
                        receiveData.length);
                Socket.receive(receivePacket);
                String sentence = new String(receivePacket.getData());
                fw.write(sentence.trim());
                fw.flush();
                System.out.printf("RECEIVED: %s ", new String(receivePacket
                        .getData()));
                // System.out.println("Done");
                // InetAddress IPAddress = receivePacket.getAddress();
                // int port = receivePacket.getPort();
                // String capitalizedSentence = sentence.toUpperCase();
                /*
                 * sendData = capitalizedSentence.getBytes(); DatagramPacket
                 * sendPacket = new DatagramPacket(sendData, sendData.length,
                 * IPAddress, port); serverSocket.send(sendPacket);
                 */
            }

EDIT

Complete Code of the Program which is running successfully.

Sender

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;


public class UDPSend {


 public static void main(String[] args) throws IOException
  {
      FileInputStream fstream = new FileInputStream("D:/T.txt");
      DataInputStream in = new DataInputStream(fstream);
      BufferedReader br = new BufferedReader(new InputStreamReader(in));

      File file = new File("D:/T.txt");
      FileInputStream fis = new FileInputStream(file);
      byte[] fsize = new byte[(int) file.length()];
      int size = fis.read(fsize);
                System.out.println("Size = " + size);



      InetAddress addr = InetAddress.getByName("localhost");
      byte[]  buf  = new byte[10000];

      String DataLine; 
      while ((DataLine = br.readLine()) != null)  
      { 
                DatagramPacket packet =new DatagramPacket(DataLine.getBytes(),         DataLine.length() , addr, 4555);
          System.out.println (DataLine);
          DatagramSocket socket = new DatagramSocket();
          socket.send(packet);

      }//end while loop


  }//end main method 

 }

Receiver

import java.io.File;
import java.io.FileWriter;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UDPReceive {

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

        FileWriter fw = new FileWriter(new File(
                "D:/outtt.txt"));
        fw.write("hi");
        try {
            // DatagramSocket serverSocket = new DatagramSocket(4555);
            DatagramSocket Socket = new DatagramSocket(4555);
            byte[] receiveData = new byte[1000000];
            // byte[] sendData = new byte[1024];
            // while(true)
            while (receiveData != null) {
                DatagramPacket receivePacket = new DatagramPacket(receiveData,
                        receiveData.length);
                Socket.receive(receivePacket);
                String sentence = new String(receivePacket.getData());
                fw.write(sentence.trim());
                fw.flush();
                System.out.printf("RECEIVED: %s ", new String(receivePacket
                        .getData()));
                // System.out.println("Done");
                // InetAddress IPAddress = receivePacket.getAddress();
                // int port = receivePacket.getPort();
                // String capitalizedSentence = sentence.toUpperCase();
                /*
                 * sendData = capitalizedSentence.getBytes(); DatagramPacket
                 * sendPacket = new DatagramPacket(sendData, sendData.length,
                 * IPAddress, port); serverSocket.send(sendPacket);
                 */
            }

            fw.flush();
            fw.close();

        } catch (Exception e) {
            System.err.println(e);
        }

    }
}

Answer 2

Look at your receiver loop:

while(receiveData != null)
{  
     DatagramPacket receivePacket = new DatagramPacket(receiveData,
                                                       receiveData.length);
     Socket.receive(receivePacket);
     String sentence = new String( receivePacket.getData());
     fw.write(sentence);
     fw.flush();
     System.out.printf("RECEIVED: %s " , new String(receivePacket.getData()));
}

Leaving aside the various character encoding issues etc, how would you ever expect receiveData to become null in that loop? How could the loop end?

Given that you're using UDP instead of TCP, you don't really have a connection, so how are you expecting to tell when the writer has stopped writing? Additionally, you should the consider the possibility of packets arriving out of order.