java send file using sockets

Question

I am trying to send a file from one computer to another using Java. I have written the code below, it works fine if both sender and receiver are started in the same computer

Answer 1

On the client side you write up to count bytes and send them:

while ((count = in.read(buffer)) > 0) {
  out.write(buffer, 0, count);

on the server side you read up to count bytes - but then you write the whole buffer to file!

while((count=in.read(buffer)) > 0){
  fos.write(buffer);

Just change it to:

fos.write(buffer, 0, count);

and you'll be on the safe side. BTW your program has another small bug: read() can return 0 which doesn't mean InputStream ended. Use >= instead:

count = in.read(buffer)) >= 0

---

Have you considered IOUtils.copy(InputStream, OutputStream) from Apache Commons? It would reduce your whole while loops to:

OutputStream out = socket.getOutputStream();
InputStream in = new FileInputStream(myFile);
IOUtils.copy(in, out);
socket.close();

Less code to write, less code to test. And buffering is done internally.

Answer 2

Remember that in.read(buffer) not necessarily fills up the whole buffer with new data. Therefore you should make sure you don't write the whole buffer. Change

while((count=in.read(buffer)) >0){
    fos.write(buffer);
}

to

while((count=in.read(buffer)) >0){
    fos.write(buffer, 0, count);
}

Answer 3

sender

Socket sock = new Socket("127.0.0.1", 5991);
        System.out.println("Connecting.........");
        File myFile = new File("/root/qrcode/");
        File[] files = myFile.listFiles();
       OutputStream os = sock.getOutputStream();
        BufferedOutputStream bos = new BufferedOutputStream(os);
                            DataOutputStream dos = new DataOutputStream(bos);

                            dos.writeInt(files.length);
                            long totalBytesRead = 0;
                            int percentCompleted = 0;
                            for(File file : files)
                            {
                                     long length = file.length();
                                     dos.writeLong(length);

                                     String name = file.getName();
                                     dos.writeUTF(name);

                                     FileInputStream fis = new FileInputStream(file);
                                     BufferedInputStream bis = new BufferedInputStream(fis);

                                     int theByte = 0;
                                     while((theByte = bis.read()) != -1)
                                     {
                                        totalBytesRead += theByte;


                                        bos.write(theByte);
                                     }
                                    //  System.out.println("file read");
                                     bis.close();
                                 }

                                dos.close();


        //Closing socket  
        sock.close();

receiver

ServerSocket serverSocket = new ServerSocket(5991);  

    while(true) {  
        Socket clientSocket = null; 
        System.out.println("Starting...");
        clientSocket = serverSocket.accept();  

        InputStream in = clientSocket.getInputStream(); //used

        BufferedInputStream bis = new BufferedInputStream(in);

        String dirPath  ;
        dirPath = "/root/NewFolder";

        try{
            DataInputStream dis = new DataInputStream(bis);

            int filesCount = dis.readInt();
            File[] files = new File[filesCount];
            long f_l = 0;
            int count =0 ;
            long totalBytesRead = 0;
            int percentCompleted = 0;

            for(int i = 0; i < filesCount; i++)
            {
                long fileLength = dis.readLong();
                String fileName = dis.readUTF();

                f_l = f_l +fileLength;
                files[i] = new File(dirPath + "/" + fileName);

                FileOutputStream fos = new FileOutputStream(files[i]);
                BufferedOutputStream bos = new BufferedOutputStream(fos);

                int tot = 0;
                for(int j = 0; j < fileLength; j++) {

                    bos.write(bis.read());
                }

                bos.close();

            }

        }catch(Exception ex)
        {
            System.out.println("error in socket programming ");
        }
    }