Client.java

import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

public class Client {
    public static void main(String[] args) {

        final File[] fileToSend= new File[1];
        JFrame jFrame = new JFrame("Client");
        jFrame.setSize(450,450);
        jFrame.setLayout(new BoxLayout(jFrame.getContentPane(), BoxLayout.Y_AXIS));
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel jlTitle = new JLabel("Send / Receive Files between Server & Client!");
        jlTitle.setFont(new Font("Arial", Font.BOLD,25));
        jlTitle.setBorder(new EmptyBorder(20,0,10,0));
        jlTitle.setAlignmentX(Component.CENTER_ALIGNMENT);
        JLabel jlFileName = new JLabel("choose a file to send.");
        jlFileName.setFont(new Font("Arial", Font.BOLD,20));
        jlFileName.setBorder(new EmptyBorder(50,0,0,0));
        jlFileName.setAlignmentX(Component.CENTER_ALIGNMENT);

        JPanel jpButton = new JPanel();
        jpButton.setBorder(new EmptyBorder(75,0,10,0));
        JButton jbSendFile = new JButton("Send");
        jbSendFile.setPreferredSize(new Dimension(150,75));
        jbSendFile.setFont(new Font("Arial",Font.BOLD,20));
        JButton jbChooseFile = new JButton("Choose File");
        jbChooseFile.setPreferredSize(new Dimension(150,75));
        jbChooseFile.setFont(new Font("Arial",Font.BOLD,20));

        jpButton.add(jbSendFile);
        jpButton.add(jbChooseFile);
        jbChooseFile.addActionListener(new ActionListener(){
           @Override
           public void actionPerformed(ActionEvent e){
               JFileChooser jFileChooser = new JFileChooser();
               jFileChooser.setDialogTitle("Choose a file to send");

               if(jFileChooser.showOpenDialog(null)==JFileChooser.APPROVE_OPTION){
                   fileToSend[0]=jFileChooser.getSelectedFile();
                   jlFileName.setText("file you want to send ---> "+fileToSend[0].getName());
               }
           }
        });

        jbSendFile.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e){
                if(fileToSend[0]==null){
                    jlFileName.setText("choose a file!");
                }

                else{
                    try{


                    FileInputStream fileInputStream=new FileInputStream(fileToSend[0].getAbsolutePath());
                    Socket socket = new Socket("localhost",3039);
                    DataOutputStream dataOutputStream= new DataOutputStream(socket.getOutputStream());
                    String fileName=fileToSend[0].getName();
                    byte[] fileNameBytes= fileName.getBytes();
                    byte[] fileContentBytes= new byte[(int)fileToSend[0].length()];
                    fileInputStream.read(fileContentBytes);
                    dataOutputStream.writeInt(fileNameBytes.length);
                    dataOutputStream.write(fileNameBytes);
                    dataOutputStream.writeInt(fileContentBytes.length);
                    dataOutputStream.write(fileContentBytes);
                    }catch(IOException err){
                        err.printStackTrace();

                    }
                }
            }

        });

        jFrame.add(jlTitle);
        jFrame.add(jlFileName);
        jFrame.add(jpButton);
        jFrame.setVisible(true);



    }
}