Thread: Need help to save Canvas content to a file

I have worked for a while to make a paint-like program. The area that i use to draw is a Canvas. Now, i want to save whatever i draw on it ...to a file on my harddisk. I have tried like this:

public class SaveJPEG extends Thread
{
	SuprafataDesenare plansa;     // this is the class which extends Canvas
	String url;                 // this is a string which is the path to the file
	FereastraPrincipala fp;     // this is the main Frame of my application
 
	public SaveJPEG(SuprafataDesenare plansa, String url,FereastraPrincipala fp)
	{
		this.plansa = plansa;
		this.url = url;
		this.fp = fp;
	}
 
	public void run()
	{
 
		try
		{
 
			BufferedImage image = new BufferedImage(plansa.getWidth(), plansa.getHeight(), BufferedImage.TYPE_INT_RGB);
			BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream(url)) ;
 
			Graphics2D graphics = image.createGraphics();
			plansa.paintAll(graphics);
			ImageIO.write(image, "jpg", fos);
 
			fos.close();
 
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
 
 
 
	}
 
 
}

But it looks like it does not work . I have seen a code like this on a site, and there was said that it should save the content of my canvas to a .jpg file. Sadly, it creates a blank .jpg file. Is there something that i have to change at my code to make it work? Is there any other way that i can save the content of my paint ?

I made a smaller program to make it easier to put here:
Here is a class which extends Canvas. Inside the method paint i draw a String. And, i add mouselisteners to make it possible to draw on the Canvas...using the mouse...just as with the pencil tool of the paint:

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
 
public class SuprafataDesenare extends Canvas implements MouseListener, MouseMotionListener
 
{
	int x1;
	int y1;
	int x2;
	int y2;
	Dimension dim = new Dimension (300,300);
 
	SuprafataDesenare()
	{
		this.setBackground(Color.white);
		this.setSize(dim);
		this.addMouseListener(this);
		this.addMouseMotionListener(this);
	}
	public void paint(Graphics g)
 
	{
		g.setColor(Color.black);
		g.setFont(new Font("Arial", Font.PLAIN, 60));
		g.drawString("HELLO!!!", 50, 50);
 
	}
 
	public void mouseClicked(MouseEvent arg0) {}
	public void mouseEntered(MouseEvent arg0) {}
	public void mouseExited(MouseEvent arg0) {}
 
	public void mousePressed(MouseEvent e)
	{
		x1 = e.getX();
		y1 = e.getY();
 
	}
 
	public void mouseReleased(MouseEvent e){}
 
	public void mouseDragged(MouseEvent e)
	{
		x2 = e.getX();
		y2 = e.getY();
 
		Graphics g = this.getGraphics();
		g.setColor(Color.black);
		g.drawLine(x1, y1, x2, y2);
		x1=x2;
		y1=y2;
		g.dispose();
 
	}
 
	public void mouseMoved(MouseEvent arg0) {}
 
 
}

Here i have the Frame, on which i place the Canvas and i also add a menu with a menuitem to save the content of the file to a jpg file:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
 
public class FereastraPrincipala extends JFrame implements ActionListener
{
	SuprafataDesenare desen = new SuprafataDesenare();
 
	public FereastraPrincipala(String titlu)
 
	{
		super(titlu);
		this.setLayout(new BorderLayout());
		this.add(desen, BorderLayout.CENTER);
		JMenuBar menuBar = new JMenuBar();
		menuBar.setBounds(0, 0, 530, 21);
		this.getContentPane().add(menuBar);
		JMenu mnFile = new JMenu("File");
		menuBar.add(mnFile);
		JMenuItem mntmSave = new JMenuItem("Save");
		mnFile.add(mntmSave);
 
		mntmSave.addActionListener(this);
 
		this.pack();
 
	}
 
 
	public void actionPerformed(ActionEvent e)
	{
		new SaveJPEG(this.desen, "C:\\Users\\nikipiulitza\\Desktop\\poze\\paint.jpg", this).start();
 
	}
 
}

And here i have the Thread which saves the file:

 
import java.awt.Canvas;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
 
import javax.imageio.ImageIO;
 
 
 
public class SaveJPEG extends Thread
{
	SuprafataDesenare plansa;     // this is the class which extends Canvas
	String url;                 // this is a string which is the path to the file
	FereastraPrincipala fp;     // this is the main Frame of my application
 
	public SaveJPEG(SuprafataDesenare plansa, String url,FereastraPrincipala fp)
	{
		this.plansa = plansa;
		this.url = url;
		this.fp = fp;
	}
 
	public void run()
	{
 
		try
		{
 
			BufferedImage image = new BufferedImage(plansa.getWidth(), plansa.getHeight(), BufferedImage.TYPE_INT_RGB);
			BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream(url)) ;
 
			Graphics2D graphics = image.createGraphics();
			plansa.paintAll(graphics);
			image.getGraphics();
			ImageIO.write(image, "jpg", fos);
 
			fos.close();
 
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
 
 
 
	}
 
 
}

I also have a class with the main method:

public class MainClass 
{
	public static void main(String[] args)
	{
		FereastraPrincipala fp = new FereastraPrincipala("String");
		fp.show();
 
 
	}
 
}

My problem is the following:
When i save the drawing to a file, i get a .jpg file on which i have drawn the String (the one that is drawn inside the paint() method of the Canvas class). But, if i draw a line using the mouse (using the "pencil" too), i only get the String saved to the file, and not what is drawn after. But i want my program to save all i draw ! What am i doing wrong ?