client-server file exchange

[Haritha Gorijavolu]

The following are the codes for client and server to exchange a file. It works like this: The client sends a connection request and the server begins to transfer the file and the client just recieves the file. The location of the file and the size of the file are predefined, for the sake of simplicity.

How is it that the client reads from the InputStream only after the Server sends the data and not before it sends data? How does it know when to start reading from InputStream? I am presently running the client and server on local host and the code is working fine.

client code:

public class Client
{

public static void main(String[] argv) throws Exception {
	    Socket sock = new Socket("127.0.0.1", 4000); //client sending a connection request
	    byte[] mybytearray = new byte[16384];
	    InputStream is = sock.getInputStream();
	    FileOutputStream fos = new FileOutputStream("C:/Users/User/Desktop/yay.png");
	    BufferedOutputStream bos = new BufferedOutputStream(fos);
	    int bytesRead = is.read(mybytearray, 0, mybytearray.length);
	    bos.write(mybytearray, 0, bytesRead); //writing to the file
	    bos.close();
	    sock.close();
	  }

}

Server code:

public class Server
{

public static void main(String[] args) throws IOException {
	    ServerSocket servsock = new ServerSocket(4000);
	    File myFile = new File("C:/Users/User/Desktop/GH34.png");
	    while (true) {
	      Socket sock = servsock.accept();
	      byte[] mybytearray = new byte[16384];
	      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();
	    }
	  }

}

[Rob Spoor]

Haritha Gorijavolu wrote:How is it that the client reads from the InputStream only after the Server sends the data and not before it sends data? How does it know when to start reading from InputStream?

What would it read if the server hasn't sent anything yet? The read method simply blocks until some data is available. Be aware that this may not everything that was sent; some bytes may still be on their way. That's why you usually should read in while loops.

[Haritha Gorijavolu]

Got it. Thanks for explaining.

[Rob Spoor]

You're welcome.