使用套接字编程进行Java文件传输

Question

In my project, I am trying to send a file to every connected clients.I used thread to send file to the clients.But when I tried to test this I found that 3 clients of total 7 got the complete pdf file but rest of them got only some bytes. What is the efficient way to implement file transfer in java socket programming so that I can send a file to more than 100 clients at the same time?

File Sending code

while(true){


            try {
                if(Helper.sendFile)
                {
                    System.out.println("file sending...");
                    File file = new File(Helper.quesPath);
                    // Get the size of the file
                    long length = file.length();
                    byte[] bytes = new byte[16 * 1024];
                    InputStream in = new FileInputStream(file);
                    OutputStream out = socket.getOutputStream();

                    int count;
                    while ((count = in.read(bytes)) > 0) {
                        out.write(bytes, 0, count);
                        System.out.println("ec : "+count);
                    }

                   //out.close();
                   out.flush();
                   in.close();
                    break;
                }
            } catch (IOException e) {

                e.printStackTrace();
            }

        try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }



    }

File receiving code

while (true)
        {
            if(Helper.sendFile)
            {
                try {
                    in = socket.getInputStream();
                    String x=System.getProperty("user.home");

                    out = new FileOutputStream(x+"/Desktop/"+Helper.courseCode+".pdf");
                    System.out.println(x);

                    byte[] bytes = new byte[16*1024];

                    int count;
                    while (true) {
                        count = in.read(bytes);
                        System.out.println("v  : "+count);
                        if(count < 16380){
                            out.write(bytes, 0, count);
                            break;
                        }else{
                            out.write(bytes, 0, count);
                        }

                    }

                    System.out.println("File Done");
                    //in.close();
                    out.close();
                    break;

                } catch (Exception ex) {
                    System.out.println("File not found. ");
                }

            }
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

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

    }

Answer 1

I think the problem you have is in when reading it from the client.

I presume that the magic number 16380 is the expected length of the file. So what you need to do is something a bit different:

int count = 0;
while (count < 16380) {
      int incoming = in.read(bytes);
      System.out.println("v  : " + incoming);

      if (incoming > 0) {
        out.write(bytes, 0, incoming); 
        count += incoming;
      } else if (incoming < 0) {
        //end of stream
        break; 
      }
}

This loop will keep on looping until the number of bytes read ( count ) reaches your magic number.

Something I would also do is use more efficient input streams, like a BufferedInputStream .

So in your first line in the block you do:

in = new BufferedInputStream(socket.getInputStream());

If you want a high number of concurrent connections it might make sense to look at making your server non-blocking with NIO. But the paradigm is a bit different.

Answer 2

I would suggest these changes:

You can set the FileOutputStream to append the received bytes to the file. This way you don't have to make sure that you write them to the correct position.

out = new FileOutputStream(x+"/Desktop/"+Helper.courseCode+".pdf", true);

The writing of the file can therefore be done like this:

int count = 0;
while ((count = in.read(bytes)) > 0) {
    System.out.println("v  : " + count);
    out.write(bytes, 0, count);
}

If this doesn't solve your problem you should show us the code in which you handle the sockets.