Java: Transfer a file from server to client and from client to server

Question

I am a newbie and I want to accomplish file transfer from server to client "do something with it" and then send the file back to the server. The most basic code I am using is here:

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Main {
  public static void main(String[] args) throws IOException {
    ServerSocket servsock = new ServerSocket(123456);
    File myFile = new File("s.pdf");
    while (true) {
      Socket sock = servsock.accept();
      byte[] mybytearray = new byte[(int) myFile.length()];
      BufferedInputStream bis = new BufferedInputStream(new FileInputStream(myFile));
      bis.read(mybytearray, 0, mybytearray.length);
      OutputStream os = sock.getOutputStream();
      os.write(mybytearray, 0, mybytearray.length);
      os.flush();
      sock.close();
    }
  }
}

The client module

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.Socket;

public class Main {
  public static void main(String[] argv) throws Exception {
    Socket sock = new Socket("127.0.0.1", 123456);
    byte[] mybytearray = new byte[1024];
    InputStream is = sock.getInputStream();
    FileOutputStream fos = new FileOutputStream("s.pdf");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    int bytesRead = is.read(mybytearray, 0, mybytearray.length);
    bos.write(mybytearray, 0, bytesRead);
    bos.close();
    sock.close();
  }
} 

Got it from this website: http://www.java2s.com/Code/Java/Network-Protocol/TransferafileviaSocket.htm

I understand how this works but I don't know how to send a file back to the server. Please help.

Answer 1

I've written a file transfer class in the past, you can use it both in your client and server (by making an instance) and use the methods to send and receive files as much as you want.

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

public class FileTransferProcessor {
    Socket socket;
    InputStream is;
    FileOutputStream fos;
    BufferedOutputStream bos;
    int bufferSize;


    FileTransferProcessor(Socket client) {
        socket = client;
        is = null;
        fos = null;
        bos = null;
        bufferSize = 0;

    }

    void receiveFile(String fileName) {
        try {
            is = socket.getInputStream();
            bufferSize = socket.getReceiveBufferSize();
            System.out.println("Buffer size: " + bufferSize);
            fos = new FileOutputStream(fileName);
            bos = new BufferedOutputStream(fos);
            byte[] bytes = new byte[bufferSize];
            int count;
            while ((count = is.read(bytes)) >= 0) {
                bos.write(bytes, 0, count);
            }
            bos.close();
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    void sendFile(File file) {

        FileInputStream fis;
        BufferedInputStream bis;
        BufferedOutputStream out;
        byte[] buffer = new byte[8192];
        try {
            fis = new FileInputStream(file);
            bis = new BufferedInputStream(fis);
            out = new BufferedOutputStream(socket.getOutputStream());
            int count;
            while ((count = bis.read(buffer)) > 0) {
                out.write(buffer, 0, count);

            }
            out.close();
            fis.close();
            bis.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}