Embracing Technology

I have been using download manager ever since my age of Internet. GetRight, Download Accelerator etc..

I liked the ability to be able to pause download and resume whenever you want, and to have a speedier download. Multiple threads to download a particular file concurrently if the file in server is supported.

I found a sample for a simple download manager, written in Java, and changed a bit to suit myself.

The original code I found are from (not sure which is the original author though) :

http://www.java2s.com/Code/Java/Tiny-Application/FileDownloadManager.htm

http://www.java-tips.org/java-se-tips/javax.swing/how-to-create-a-download-manager-in-java.html

 Some brief pointers:

Concept

This sample program shows how to download a file through HTTP which is able to pause and resume download. The key to doing this is actually specifying the point where to resume the download:
            // Specify what portion of file to download.
            connection.setRequestProperty(“Range”, “bytes=” + downloaded + “-”);

and
            file.seek(downloaded);

Screen Shots

Source Code



import java.awt.BorderLayout;

import java.awt.Component;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.awt.event.KeyEvent;

import java.awt.event.WindowAdapter;

import java.awt.event.WindowEvent;

import java.io.File;

import java.io.FileOutputStream;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import java.util.ArrayList;

import java.util.Observable;

import java.util.Observer;

import java.util.Properties;

import javax.swing.BorderFactory;

import javax.swing.JButton;

import javax.swing.JFileChooser;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JMenu;

import javax.swing.JMenuBar;

import javax.swing.JMenuItem;

import javax.swing.JOptionPane;

import javax.swing.JPanel;

import javax.swing.JProgressBar;

import javax.swing.JScrollPane;

import javax.swing.JTable;

import javax.swing.JTextField;

import javax.swing.ListSelectionModel;

import javax.swing.event.ListSelectionEvent;

import javax.swing.event.ListSelectionListener;

import javax.swing.table.AbstractTableModel;

import javax.swing.table.TableCellRenderer;

public class DownloadManager extends JFrame implements Observer {

    private JTextField addTextField = new JTextField(30);

    private DownloadsTableModel tableModel = new DownloadsTableModel();

    private JTable table;

    private JButton pauseButton = new JButton("Pause");

    private JButton resumeButton = new JButton("Resume");

    private JButton cancelButton, clearButton;

    private JLabel saveFileLabel = new JLabel();

    private Download selectedDownload;

    private boolean clearing;

    public DownloadManager() {

        setTitle("Marvin's Download Manager");

        setSize(640, 480);

        addWindowListener(new WindowAdapter() {

            public void windowClosing(WindowEvent e) {

                System.exit(0);

            }

        });

        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) {

                System.exit(0);

            }

        });

        fileMenu.add(fileExitMenuItem);

        menuBar.add(fileMenu);

        setJMenuBar(menuBar);

        // Set up add panel.

        JPanel addPanel = new JPanel(new BorderLayout());
        JPanel targetPanel = new JPanel(new BorderLayout());

        targetPanel.add(addTextField, BorderLayout.WEST);

        JButton addButton = new JButton("Add Download");

        addButton.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {

                actionAdd();

            }

        });
        targetPanel.add(addButton, BorderLayout.EAST);
        JPanel destinationPanel = new JPanel(new BorderLayout());

        saveFileLabel.setText("File:");

        destinationPanel.add(saveFileLabel, BorderLayout.WEST);
        JButton saveFileButton = new JButton("Download To");

        saveFileButton.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {

                actionSaveTo();

            }

        });

        destinationPanel.add(saveFileButton, BorderLayout.EAST);

        addPanel.add(destinationPanel, BorderLayout.NORTH);

        addPanel.add(targetPanel, BorderLayout.SOUTH);

        // Set up Downloads table.



        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); // show progress text

        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.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {

                actionPause();

            }

        });

        pauseButton.setEnabled(false);

        buttonsPanel.add(pauseButton);
        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 actionSaveTo()

    {
        JFileChooser jfchooser = new JFileChooser();
        jfchooser.setApproveButtonText("OK");

        jfchooser.setDialogTitle("Save To");

        jfchooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);

        int result = jfchooser.showOpenDialog(this);

        File newZipFile = jfchooser.getSelectedFile();

        System.out.println("importProfile:" + newZipFile);

        this.saveFileLabel.setText(newZipFile.getPath());

    }

    private void actionAdd() {

        URL verifiedUrl = verifyUrl(addTextField.getText());

        if (verifiedUrl != null) {

            tableModel.addDownload(new Download(verifiedUrl, saveFileLabel.getText()));

            addTextField.setText(""); // reset add text field

        } 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(true);

                    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: // COMPLETE or CANCELLED

                    pauseButton.setEnabled(false);

                    resumeButton.setEnabled(false);

                    cancelButton.setEnabled(false);

                    clearButton.setEnabled(true);

            }

        } else {

            pauseButton.setEnabled(false);

            resumeButton.setEnabled(false);

            cancelButton.setEnabled(false);

            clearButton.setEnabled(false);

        }

    }

    public void update(Observable o, Object arg) {

        // Update buttons if the selected download has changed.

        if (selectedDownload != null && selectedDownload.equals(o))

            updateButtons();

    }

    // Run the Download Manager.

    public static void main(String[] args) {

        DownloadManager manager = new DownloadManager();

        manager.setVisible(true);

    }

}

class Download extends Observable implements Runnable {

    private static final int MAX_BUFFER_SIZE = 1024;

    public static final String STATUSES[] = { "Downloading", "Paused", "Complete", "Cancelled",

    "Error" };

    public static final int DOWNLOADING = 0;

    public static final int PAUSED = 1;

    public static final int COMPLETE = 2;

    public static final int CANCELLED = 3;

    public static final int ERROR = 4;

    private URL url; // download URL



    private String saveDir; // dir to save



    private int size; // size of download in bytes



    private int downloaded; // number of bytes downloaded



    private int status; // current status of download

    // Proxy information

    public static final boolean proxyRequired = true; // Change for your settings

    public static final String proxyIP = "127.0.0.1";

    public static final String proxyPort = "8080";

    public static final String proxyUsername = "proxyUser";

    public static final String proxyPassword = "proxyPassword";

    // Constructor for Download.

    public Download(URL url, String saveDir) {

        this.url = url;

        this.saveDir = saveDir;

        size = -1;

        downloaded = 0;

        status = DOWNLOADING;

        // Begin the download.

        download();

    }

    // Get this download's URL.

    public String getUrl() {

        return url.toString();

    }

    // Get this download's size.

    public int getSize() {

        return size;

    }

    // Get this download's progress.

    public float getProgress() {

        return ((float) downloaded / size) * 100;

    }

    public int getStatus() {

        return status;

    }

    public void pause() {

        status = PAUSED;

        stateChanged();

    }

    public void resume() {

        status = DOWNLOADING;

        stateChanged();

        download();

    }

    public void cancel() {

        status = CANCELLED;

        stateChanged();

    }

    private void error() {

        status = ERROR;

        stateChanged();

    }

    private void download() {

        Thread thread = new Thread(this);

        thread.start();

    }

    // Get file name portion of URL.

    public String getFileName(URL url) {

        String fileName = url.getFile();

        return fileName.substring(fileName.lastIndexOf('/') + 1);

    }

    // Download file.

    public void run() {

        RandomAccessFile file = null;

        InputStream stream = null;

        FileOutputStream out = null;

        try {

            if (proxyRequired){

                // This can be put in a menu, updated via interface

                System.out.println("Setting proxy");

                Properties systemSettings = System.getProperties();

                systemSettings.put("http.proxyHost", proxyIP);

                systemSettings.put("http.proxyPort", proxyPort);

                System.setProperties(systemSettings);

            }

            // Open connection to URL.

            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // Specify what portion of file to download.

            connection.setRequestProperty("Range", "bytes=" + downloaded + "-");

            if (proxyRequired){

                String encoded = new String(new sun.misc.BASE64Encoder().encode(new String( proxyUsername + ":" + proxyPassword).getBytes()));

                connection.setRequestProperty("Proxy-Authorization", "Basic " + encoded);

            }

            System.out.println("Going to make connection");

            // Connect to server.

            connection.connect();

            System.out.println("Connected!");

            int responseCode = connection.getResponseCode();

            System.out.println("Response code from server=" + responseCode);

            // Make sure response code is in the 200 range.

            // 200 - no partial download

            // 206 - supports resume

            //if (responseCode / 100 != 2) {

            if (responseCode == 200 || responseCode == 206) {

                error();

            }

            // Check for valid content length.

            System.out.println("Content length=" + connection.getContentLength());

            int contentLength = connection.getContentLength();

            if (contentLength < 1) {

                error();

            }

      /*

       * Set the size for this download if it hasn't been already set.

       */

            if (size == -1) {

                size = contentLength;

                stateChanged();

            }

            // Open file and seek to the end of it.

            file = new RandomAccessFile(getFileName(url), "rw");

            file.seek(downloaded);

            System.out.println("Get InputStream");

            stream = connection.getInputStream();

            status = DOWNLOADING;

            out = new FileOutputStream(saveDir + File.separator + this.getFileName(url));

            while (status == DOWNLOADING) {

                /*

                 * Size buffer according to how much of the file is left to download.

                 */

                byte buffer[];

                if (size - downloaded > MAX_BUFFER_SIZE) {

                    buffer = new byte[MAX_BUFFER_SIZE];

                } else {

                    buffer = new byte[size - downloaded];

                }

                // Read from server into buffer.

                int read = stream.read(buffer);

                if (read == -1)

                    break;

                // Write buffer to file.

                //file.write(buffer, 0, read);

                out.write(buffer, 0, read);

                downloaded += read;

                stateChanged();

            }

      /*

       * Change status to complete if this point was reached because downloading

       * has finished.

       */

            if (status == DOWNLOADING) {

                status = COMPLETE;
                stateChanged();

            }

        } catch (Exception e) {

            System.out.println("Error=" + e);

            e.printStackTrace();

            error();

        } finally {

            // Close file.

            if (file != null) {

                try {

                    // Complete the file

                    out.close();

                    file.close();

                } catch (Exception e) {

                    e.printStackTrace();

                }

            }

            // Close connection to server.

            if (stream != null) {

                try {

                    stream.close();

                } catch (Exception e) {

                    e.printStackTrace();

                }

            }

        }

    }

    private void stateChanged() {

        setChanged();

        notifyObservers();

    }

}

class DownloadsTableModel extends AbstractTableModel implements Observer {

    private static final String[] columnNames = { "URL", "Size", "Progress", "Status" };

    private static final Class[] columnClasses = { String.class, String.class, JProgressBar.class,

    String.class };

    private ArrayList<Download> downloadList = new ArrayList<Download>();

    public void addDownload(Download download) {

        download.addObserver(this);

        downloadList.add(download);

        fireTableRowsInserted(getRowCount() - 1, getRowCount() - 1);

    }

    public Download getDownload(int row) {

        return (Download) downloadList.get(row);

    }

    public void clearDownload(int row) {

        downloadList.remove(row);

        fireTableRowsDeleted(row, row);

    }

    public int getColumnCount() {

        return columnNames.length;

    }

    public String getColumnName(int col) {

        return columnNames[col];

    }

    public Class getColumnClass(int col) {

        return columnClasses[col];

    }

    public int getRowCount() {

        return downloadList.size();

    }

    public Object getValueAt(int row, int col) {

        Download download = downloadList.get(row);

        switch (col) {

            case 0: // URL

                return download.getUrl();

            case 1: // Size

                int size = download.getSize();

                return (size == -1) ? "" : Integer.toString(size);

            case 2: // Progress

                return new Float(download.getProgress());

            case 3: // Status

                return Download.STATUSES[download.getStatus()];

        }

        return "";

    }

    public void update(Observable o, Object arg) {

        int index = downloadList.indexOf(o);

        fireTableRowsUpdated(index, index);

    }

}

class ProgressRenderer extends JProgressBar implements TableCellRenderer {

    public ProgressRenderer(int min, int max) {

        super(min, max);

    }

    public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected,

            boolean hasFocus, int row, int column) {

        setValue((int) ((Float) value).floatValue());

        return this;

    }

}

To Run

• Copy the code above, and paste into a DownloadManager.java file
• If you’re behind a proxy, change the proxy settings.
• If you’re not behind a proxy, set the proxyRequired = false;
• Compile and run

To Download Files

• Select the folder you want to save the file
• Copy the URL of the file you want to download
• Paste to the textbox
• Click “Add to Download”
• File will automatically be downloaded
• You can click “Pause” to temporary stop download

Enhancement

• Persists directly the file downloaded even if not 100% completed 
• File splitting, download a single file with multiple threads

Other useful references

http://www.intel.com/cd/ids/developer/asmo-na/eng/20188.htm?page=1

http://www.intel.com/cd/ids/developer/asmo-na/eng/20187.htm