How to communicate with a Virtual Machine in Java?

Question

I have made a little Java program that asks a person to enter a pin code. As soon as the pin code is entered, it reads into a "bdd.txt" file in which all the pins are stored and then it displays :) if good and :( if wrong. Simple application so far.

What I want to do is to move that "database" file into a Virtual Machine on my computer (such as Ubuntu for example), and then do the same thing. This way, it won't be local anymore, since the file will not be located at the root of my project anymore.

Here is what my application looks like :

As you can see, the app starts, the user is asked to enter is pin code. If this is a good one, the app is done, if not he has 2 more tries left until the app stops.

When the pin is entered, my program checks in "bdd.txt" if the pin is there or not. It plays the database role:

To understand what I need, it is necessary to assimilate this program to something that needs to be secure. We do not want the pins database at the same place as the program (or the device in real life). So we put it on a Virtual Machine and we have to communicate between my Windows7 Java program in Eclipse and the bdd.txt file on VMWare Player's Ubuntu.

My question is how is that possible ? How do I need to change my code to let my program reach something on my VM ? Is there a specifig technology I should use for it ? Do I need to do some configurations first ?

Here is my code :

import java.io.*;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import javax.swing.*;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
import javax.swing.text.PlainDocument;
import java.awt.*;
import java.awt.event.*;

public class Main extends JFrame {

    private static final long serialVersionUID = 1L;

    private JPanel container = new JPanel();
    private JPasswordField p1 = new JPasswordField(4);
    private JLabel label = new JLabel("Enter Pin: ");
    private JButton b = new JButton("OK");


    public Main() {
        this.setTitle("NEEDS");
        this.setSize(300, 500);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);

        container.setBackground(Color.white);
        container.setLayout(new BorderLayout());
        container.add(p1);
        JPanel top = new JPanel();

        PlainDocument document =(PlainDocument)p1.getDocument();

        b.addActionListener(new BoutonListener());

        top.add(label);
        top.add(p1);
        p1.setEchoChar('*');
        top.add(b);  

        document.setDocumentFilter(new DocumentFilter(){

            @Override
            public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
                String string =fb.getDocument().getText(0, fb.getDocument().getLength())+text;

                if(string.length() <= 4)
                super.replace(fb, offset, length, text, attrs); //To change body of generated methods, choose Tools | Templates.
            }
        });


        this.setContentPane(top);
        this.setVisible(true);
    }

    class BoutonListener implements ActionListener {
        private final AtomicInteger nbTry = new AtomicInteger(0);
        ArrayList<Integer> pins = readPinsData(new File("bdd.txt"));

        @SuppressWarnings("deprecation")
        public void actionPerformed(ActionEvent e) {
            if (nbTry.get() > 2) {
                JOptionPane.showMessageDialog(null,
                        "Pin blocked due to 3 wrong tries");
                return;
            }
            final String passEntered=p1.getText().replaceAll("\u00A0", "");
            if (passEntered.length() != 4) {
                JOptionPane.showMessageDialog(null, "Pin must be 4 digits");
                return;
            }
            //JOptionPane.showMessageDialog(null, "Checking...");
            //System.out.println("Checking...");
            SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {
                @Override
                protected Void doInBackground() throws Exception {
                    boolean authenticated = false;

                    if (pins.contains(Integer.parseInt(passEntered))) {
                        JOptionPane.showMessageDialog(null, ":)");
                        authenticated = true;
                    }

                    if (!authenticated) {
                        JOptionPane.showMessageDialog(null, ":(");
                        nbTry.incrementAndGet();
                    }
                    return null;
                }
            };
            worker.execute();
        }

    }

    //Function to read/access my bdd.txt file
    static public ArrayList<Integer> readPinsData(File dataFile) {
        final ArrayList<Integer> data=new ArrayList<Integer>();
        try {
            BufferedReader reader = new BufferedReader(new FileReader(dataFile));
            String line;
            try {
                while ((line = reader.readLine()) != null) {
                    try {
                        data.add(Integer.parseInt(line));
                    } catch (NumberFormatException e) {
                        e.printStackTrace();
                        System.err.printf("error parsing line '%s'\n", line);
                    }
                }
            } finally {
                reader.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
            System.err.println("error:"+e.getMessage());
        }

        return data;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Main();
            }
        });

    }
}

Any ideas ? Thanks,

Florent.

Answer 1

A shared folder will certainly work, but there seems little point in having a VM at all, because the PIN file is also on your host machine, and java is reading it directly.

Maybe you need a client/server architecture?

You program with the UI will be the client. The client will be configured with a means of calling the server (IP address and port). The client does not have access to the bdd.txt file, but the server does.

On your VM, you have another java application, the Server. Your server listens for requests from the client. The request will contain a PIN entered by the user. The server then checks it against the PINs in the file, and responds with a yes or no. Your client receives the yes/no response from the server, and reports the result back to the user.

Read about Sockets programming here to get started

Answer 2

There are two things you would need to do:

1. Share a folder between your host OS and your VM. This will allow your Virtual Machine to access files from the host operating system. You would want to put your pin file in this folder.

2. Have your application read the pin file from the shared folder. This would mean changing this line:

   ArrayList<Integer> pins = readPinsData(new File("bdd.txt"));

   Right now, this code is reading the file bdd.txt from the current directory the user is in, which I assume is the directory your executable is in. Instead, you want this to point to the pin file in your shared directory. To make your code as flexible as possible, you may want to pass in the path to the pin file as a command line argument when you start the program.