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();

  }

}