DownloadManager.java

import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;

public class DownloadManager extends JFrame implements Observer {
	private JTextField addTextField;
	private DownloadsTableModel tableModel;
	private JTable table;
	private JButton pauseButton, resumeButton, cancelButton, clearButton;
	private Download selectedDownload;
	private boolean clearing;

	public DownloadManager() {
		setTitle("Alif Download Manager");
		setSize(640,480);
		addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				actionExit();
			}
		});
		
		JMenuBar menuBar = new JMenuBar();
		JMenu fileMenu = new JMenu("File");
		fileMenu.setMnemonic(KeyEvent.VK_F);
		JMenuItem fileExitMenuItem = new JMenuItem("EXIT", KeyEvent.VK_X);
		fileExitMenuItem.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionExit();
			}
		});
		
		fileMenu.add(fileExitMenuItem);
		menuBar.add(fileMenu);
		setJMenuBar(menuBar);
		
		JPanel addPanel = new JPanel();
		addTextField = new JTextField(30);
		addPanel.add(addTextField);
		JButton addButton = new JButton("Add Download");
		addButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionAdd();
			}
		});
		addPanel.add(addButton);
		
		tableModel = new DownloadsTableModel();
		table = new JTable(tableModel);
		table.getSelectionModel().addListSelectionListener( new ListSelectionListener() {
			public void valueChanged(ListSelectionEvent e) {
				tableSelectionChanged();
			}
		});
		table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
		
		ProgressRenderer renderer = new ProgressRenderer(0, 100);
		renderer.setStringPainted(true);
		table.setDefaultRenderer(JProgressBar.class, renderer);
		
		table.setRowHeight((int) renderer.getPreferredSize().getHeight());
		
		JPanel downloadsPanel = new JPanel();
		downloadsPanel.setBorder(BorderFactory.createTitledBorder("Downloads"));
		downloadsPanel.setLayout(new BorderLayout());
		downloadsPanel.add(new JScrollPane(table), BorderLayout.CENTER);
		
		JPanel buttonsPanel = new JPanel();
		pauseButton = new JButton("Pause");
		pauseButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionPause();
			}
		});
		pauseButton.setEnabled(false);
		buttonsPanel.add(pauseButton);
		
		resumeButton = new JButton("Resume");
		resumeButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionResume();
			}
		});
		resumeButton.setEnabled(false);
		buttonsPanel.add(resumeButton);
		
		cancelButton = new JButton("Cancel");
		cancelButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionCancel();
			}
		});
		cancelButton.setEnabled(false);
		buttonsPanel.add(cancelButton);
		
		clearButton = new JButton("Clear");
		clearButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				actionClear();
			}
		});
		clearButton.setEnabled(false);
		buttonsPanel.add(clearButton);
		
		getContentPane().setLayout(new BorderLayout());
		getContentPane().add(addPanel, BorderLayout.NORTH);
		getContentPane().add(downloadsPanel, BorderLayout.CENTER);
		getContentPane().add(buttonsPanel, BorderLayout.SOUTH);
	}
		
	private void actionExit() {
		System.exit(0);
	}
		
	private void actionAdd() {
		URL verifiedUrl = verifyUrl(addTextField.getText());
		if(verifiedUrl != null) {
			tableModel.addDownload(new Download(verifiedUrl));
			addTextField.setText("");
		} else {
			JOptionPane.showMessageDialog(this, "Invalid Download URL", "Error", JOptionPane.ERROR_MESSAGE);
		}
	}

	private URL verifyUrl(String url) {
		if(!url.toLowerCase().startsWith("http://"))
			return null;
		URL verifiedUrl = null;
		try{
			verifiedUrl = new URL(url);
		} catch(Exception e) {
			return null;
		}
		
		if(verifiedUrl.getFile().length() < 2)
			return null;
		
		return verifiedUrl;
	}
	
	private void tableSelectionChanged() {
		if(selectedDownload != null)
			selectedDownload.deleteObserver(DownloadManager.this);
		if(!clearing && table.getSelectedRow() > -1) {
			selectedDownload = tableModel.getDownload(table.getSelectedRow());
			selectedDownload.addObserver(DownloadManager.this);
			updateButtons();
		}
	}
	
	private void actionPause() {
		selectedDownload.pause();
		updateButtons();
	}
	
	private void actionResume() {
		selectedDownload.resume();
		updateButtons();
	}
		
	private void actionCancel() {
		selectedDownload.cancel();
		updateButtons();
	}
	
	private void actionClear() {
		clearing = true;
		tableModel.clearDownload(table.getSelectedRow());
		clearing = false;
		selectedDownload = null;
		updateButtons();
	}
	
	private void updateButtons() {
		if(selectedDownload != null) {
			int status = selectedDownload.getStatus();
			switch(status) {
			
				case Download.DOWNLOADING:
					pauseButton.setEnabled(true);
					resumeButton.setEnabled(false);
					cancelButton.setEnabled(false);
					clearButton.setEnabled(false);
					break;
				
				case Download.PAUSED:
					pauseButton.setEnabled(false);
					resumeButton.setEnabled(true);
					cancelButton.setEnabled(true);
					clearButton.setEnabled(false);
					break;
					
				case Download.ERROR:
					pauseButton.setEnabled(false);
					resumeButton.setEnabled(true);
					cancelButton.setEnabled(false);
					clearButton.setEnabled(true);
					break;
		
				default:
					pauseButton.setEnabled(false);
					resumeButton.setEnabled(false);
					cancelButton.setEnabled(false);
					clearButton.setEnabled(true);
					break;
			}
		} else {
			pauseButton.setEnabled(false);
			resumeButton.setEnabled(false);
			cancelButton.setEnabled(false);
			clearButton.setEnabled(false);
		}
	}
	
	public void update(Observable o, Object arg) {
		if(selectedDownload != null && selectedDownload.equals(o))
			updateButtons();
	}
	
	public static void main(String[] args) {
		SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				DownloadManager manager = new DownloadManager();
				manager.setVisible(true);
			}
		});
	}	
}