Transfer the File "Client Socket to Server Socket" in Java

import java.io.*;
import java.net.Socket;

public class Client {
    private static DataOutputStream dataOutputStream = null;
    private static DataInputStream dataInputStream = null;

    public static void main(String[] args)
    {
        // Create Client Socket connect to port 900 
        try (Socket socket = new Socket("localhost", 900)) {
           
          dataInputStream = new DataInputStream(
                socket.getInputStream());
            dataOutputStream = new DataOutputStream(
                socket.getOutputStream());
            System.out.println(
                "Sending the File to the Server");
          // Call SendFile Method
          sendFile(
                "/home/dachman/Desktop/Program/gfg/JAVA_Program/File Transfer/txt.pdf");

            dataInputStream.close();
            dataInputStream.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    // sendFile function define here
    private static void sendFile(String path)
        throws Exception
    {
        int bytes = 0;
        // Open the File where he located in your pc
        File file = new File(path);
        FileInputStream fileInputStream
            = new FileInputStream(file);

        // Here we send the File to Server
        dataOutputStream.writeLong(file.length());
        // Here we  break file into chunks
        byte[] buffer = new byte[4 * 1024];
        while ((bytes = fileInputStream.read(buffer))
               != -1) {
          // Send the file to Server Socket  
          dataOutputStream.write(buffer, 0, bytes);
            dataOutputStream.flush();
        }
        // close the file here
        fileInputStream.close();
    }
}

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

    private static DataOutputStream dataOutputStream = null;
    private static DataInputStream dataInputStream = null;

    public static void main(String[] args)
    {
        // Here we define Server Socket running on port 900
        try (ServerSocket serverSocket
             = new ServerSocket(900)) {
            System.out.println(
                "Server is Starting in Port 900");
            // Accept the Client request using accept method
            Socket clientSocket = serverSocket.accept();
            System.out.println("Connected");
            dataInputStream = new DataInputStream(
                clientSocket.getInputStream());
            dataOutputStream = new DataOutputStream(
                clientSocket.getOutputStream());
            // Here we call receiveFile define new for that
            // file
            receiveFile("NewFile1.pdf");

            dataInputStream.close();
            dataOutputStream.close();
            clientSocket.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    // receive file function is start here

    private static void receiveFile(String fileName)
        throws Exception
    {
        int bytes = 0;
        FileOutputStream fileOutputStream
            = new FileOutputStream(fileName);

        long size
            = dataInputStream.readLong(); // read file size
        byte[] buffer = new byte[4 * 1024];
        while (size > 0
               && (bytes = dataInputStream.read(
                       buffer, 0,
                       (int)Math.min(buffer.length, size)))
                      != -1) {
            // Here we write the file using write method
            fileOutputStream.write(buffer, 0, bytes);
            size -= bytes; // read upto file size
        }
        // Here we received file
        System.out.println("File is Received");
        fileOutputStream.close();
    }
}