Java: read from binary file, send bytes over socket

Question

This should be easy, but I can't get my head around it right now. I wanna send some bytes over a socket, like

Socket s = new Socket("localhost", TCP_SERVER_PORT);
DataInputStream is = new DataInputStream(new BufferedInputStream(s.getInputStream()));

DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(s.getOutputStream()));

for (int j=0; j<40; j++) {
  dos.writeByte(0);
}

That works, but now I dont want to writeByte to the Outputstream, but read from a binary file, then write it out. I know(?) I need a FileInputStream to read from, I just can't figure out hot to construct the whole thing.

Can someone help me out?

Answer 1

public void transfer(final File f, final String host, final int port) throws IOException {
    final Socket socket = new Socket(host, port);
    final BufferedOutputStream outStream = new BufferedOutputStream(socket.getOutputStream());
    final BufferedInputStream inStream = new BufferedInputStream(new FileInputStream(f));
    final byte[] buffer = new byte[4096];
    for (int read = inStream.read(buffer); read >= 0; read = inStream.read(buffer))
        outStream.write(buffer, 0, read);
    inStream.close();
    outStream.close();
}

This would be the naive approach without proper exception handling - in a real-world setting you'd have to make sure to close the streams if an error occurs.

You might want to check out the Channel classes as well as an alternative to streams. FileChannel instances, for example, provide the transferTo(...) method that may be a lot more efficient.