How do I set proxy settings for a Java app behind a corporate server?

Question

I have the source code of a Download Manager program written in Java. It has to be run within my college network in which we use the "Corporate Client" server to access the internet. The HTTP proxy is 172.16.68.6 and Port number is 3128. How do I define these parameters in my java program so that it can download files from the internet?
The source code for the program is:
There are four classes:
1. DownloadManager.java
2. Download.java
3. DownloadTable.java
4. ProgressRenderer.java
/*__DownloadManager.java__*/
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
// The Download Manager.
public class DownloadManager extends JFrame
        implements Observer {
    // Add download text field.
    private JTextField addTextField;
    // Download table's data model.
    private DownloadsTableModel tableModel;
    // Table listing downloads.
    private JTable table;
    // These are the buttons for managing the selected download.
    private JButton pauseButton, resumeButton;
    private JButton cancelButton, clearButton;
    // Currently selected download.
    private Download selectedDownload;
    // Flag for whether or not table selection is being cleared.
    private boolean clearing;
    // Constructor for Download Manager.
    public DownloadManager() {
        // Set application title.
        setTitle("Download Manager");
        // Set window size.
        setSize(640, 480);
        // Handle window closing events.
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                actionExit();
        // Set up file menu.
        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);
        // Set up add panel.
        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);
        // Set up Downloads table.
        tableModel = new DownloadsTableModel();
        table = new JTable(tableModel);
        table.getSelectionModel().addListSelectionListener(new
                ListSelectionListener() {
            public void valueChanged(ListSelectionEvent e) {
                tableSelectionChanged();
        // Allow only one row at a time to be selected.
        table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        // Set up ProgressBar as renderer for progress column.
        ProgressRenderer renderer = new ProgressRenderer(0, 100);
        renderer.setStringPainted(true); // show progress text
        table.setDefaultRenderer(JProgressBar.class, renderer);
        // Set table's row height large enough to fit JProgressBar.
        table.setRowHeight(
                (int) renderer.getPreferredSize().getHeight());
        // Set up downloads panel.
        JPanel downloadsPanel = new JPanel();
        downloadsPanel.setBorder(
                BorderFactory.createTitledBorder("Downloads"));
        downloadsPanel.setLayout(new BorderLayout());
        downloadsPanel.add(new JScrollPane(table),
                BorderLayout.CENTER);
        // Set up buttons panel.
        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);
        // Add panels to display.
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(addPanel, BorderLayout.NORTH);
        getContentPane().add(downloadsPanel, BorderLayout.CENTER);
        getContentPane().add(buttonsPanel, BorderLayout.SOUTH);
    // Exit this program.
    private void actionExit() {
        System.exit(0);
    // Add a new download.
    private void actionAdd() {
        URL verifiedUrl = verifyUrl(addTextField.getText());
        if (verifiedUrl != null) {
            tableModel.addDownload(new Download(verifiedUrl));
            addTextField.setText(""); // reset add text field
        } else {
            JOptionPane.showMessageDialog(this,
                    "Invalid Download URL", "Error",
                    JOptionPane.ERROR_MESSAGE);
    // Verify download URL.
    private URL verifyUrl(String url) {
        // Only allow HTTP URLs.
        if (!url.toLowerCase().startsWith("http://"))
            return null;
        // Verify format of URL.
        URL verifiedUrl = null;
        try {
            verifiedUrl = new URL(url);
        } catch (Exception e) {
            return null;
        // Make sure URL specifies a file.
        if (verifiedUrl.getFile().length() < 2)
            return null;
        return verifiedUrl;
    // Called when table row selection changes.
    private void tableSelectionChanged() {
    /* Unregister from receiving notifications
       from the last selected download. */
        if (selectedDownload != null)
            selectedDownload.deleteObserver(DownloadManager.this);
    /* If not in the middle of clearing a download,
       set the selected download and register to
       receive notifications from it. */
        if (!clearing) {
            selectedDownload =
                    tableModel.getDownload(table.getSelectedRow());
            selectedDownload.addObserver(DownloadManager.this);
            updateButtons();
    // Pause the selected download.
    private void actionPause() {
        selectedDownload.pause();
        updateButtons();
    // Resume the selected download.
    private void actionResume() {
        selectedDownload.resume();
        updateButtons();
    // Cancel the selected download.
    private void actionCancel() {
        selectedDownload.cancel();
        updateButtons();
    // Clear the selected download.
    private void actionClear() {
        clearing = true;
        tableModel.clearDownload(table.getSelectedRow());
        clearing = false;
        selectedDownload = null;
        updateButtons();
  /* Update each button's state based off of the
     currently selected download's status. */
    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 {
            // No download is selected in table.
            pauseButton.setEnabled(false);
            resumeButton.setEnabled(false);
            cancelButton.setEnabled(false);
            clearButton.setEnabled(false);
  /* Update is called when a Download notifies its
     observers of any changes. */
    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.show();
This example shows how to create a simple download manager in Java. It contains four classes in foru Java source files:
Download.java: Contains Download class which downloads a file from a URL.
DownloadManager.java: Contains the main class for download manager application.
DownloadsTableModel.java: Contains the class which manages the download table's data.
ProgressRenderer.java: Contains the class which is responsible to render a JProgressBar in a table cell.
The contents of the listed files are written below.
/*__Download.java__*/
import java.io.*;
import java.net.*;
import java.util.*;
// This class downloads a file from a URL.
class Download extends Observable implements Runnable {
    // Max size of download buffer.
    private static final int MAX_BUFFER_SIZE = 1024;
    // These are the status names.
    public static final String STATUSES[] = {"Downloading",
    "Paused", "Complete", "Cancelled", "Error"};
    // These are the status codes.
    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 int size; // size of download in bytes
    private int downloaded; // number of bytes downloaded
    private int status; // current status of download
    // Constructor for Download.
    public Download(URL url) {
        this.url = url;
        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;
    // Get this download's status.
    public int getStatus() {
        return status;
    // Pause this download.
    public void pause() {
        status = PAUSED;
        stateChanged();
    // Resume this download.
    public void resume() {
        status = DOWNLOADING;
        stateChanged();
        download();
    // Cancel this download.
    public void cancel() {
        status = CANCELLED;
        stateChanged();
    // Mark this download as having an error.
    private void error() {
        status = ERROR;
        stateChanged();
    // Start or resume downloading.
    private void download() {
        Thread thread = new Thread(this);
        thread.start();
    // Get file name portion of URL.
    private 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;
        try {
            // Open connection to URL.
            HttpURLConnection connection =
                    (HttpURLConnection) url.openConnection();
            // Specify what portion of file to download.
            connection.setRequestProperty("Range",
                    "bytes=" + downloaded + "-");
            // Connect to server.
            connection.connect();
            // Make sure response code is in the 200 range.
            if (connection.getResponseCode() / 100 != 2) {
                error();
            // Check for valid content length.
            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);
            stream = connection.getInputStream();
            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);
                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) {
            error();
        } finally {
            // Close file.
            if (file != null) {
                try {
                    file.close();
                } catch (Exception e) {}
            // Close connection to server.
            if (stream != null) {
                try {
                    stream.close();
                } catch (Exception e) {}
    // Notify observers that this download's status has changed.
    private void stateChanged() {
        setChanged();
        notifyObservers();
/*__DownloadTableModel.java__*/
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;
// This class manages the download table's data.
class DownloadsTableModel extends AbstractTableModel
        implements Observer {
    // These are the names for the table's columns.
    private static final String[] columnNames = {"URL", "Size",
    "Progress", "Status"};
    // These are the classes for each column's values.
    private static final Class[] columnClasses = {String.class,
    String.class, JProgressBar.class, String.class};
    // The table's list of downloads.
    private ArrayList downloadList = new ArrayList();
    // Add a new download to the table.
    public void addDownload(Download download) {
        // Register to be notified when the download changes.
        download.addObserver(this);
        downloadList.add(download);
        // Fire table row insertion notification to table.
        fireTableRowsInserted(getRowCount() - 1, getRowCount() - 1);
    // Get a download for the specified row.
    public Download getDownload(int row) {
        return (Download) downloadList.get(row);
    // Remove a download from the list.
    public void clearDownload(int row) {
        downloadList.remove(row);
        // Fire table row deletion notification to table.
        fireTableRowsDeleted(row, row);
    // Get table's column count.
    public int getColumnCount() {
        return columnNames.length;
    // Get a column's name.
    public String getColumnName(int col) {
        return columnNames[col];
    // Get a column's class.
    public Class getColumnClass(int col) {
        return columnClasses[col];
    // Get table's row count.
    public int getRowCount() {
        return downloadList.size();
    // Get value for a specific row and column combination.
    public Object getValueAt(int row, int col) {
        Download 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 "";
  /* Update is called when a Download notifies its
     observers of any changes */
    public void update(Observable o, Object arg) {
        int index = downloadList.indexOf(o);
        // Fire table row update notification to table.
        fireTableRowsUpdated(index, index);
/*__ProgressRenderer.java__*/
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;
// This class renders a JProgressBar in a table cell.
class ProgressRenderer extends JProgressBar
        implements TableCellRenderer {
    // Constructor for ProgressRenderer.
    public ProgressRenderer(int min, int max) {
        super(min, max);
  /* Returns this JProgressBar as the renderer
     for the given table cell. */
    public Component getTableCellRendererComponent(
            JTable table, Object value, boolean isSelected,
            boolean hasFocus, int row, int column) {
        // Set JProgressBar's percent complete value.
        setValue((int) ((Float) value).floatValue());
        return this;
}

Answer 1

Thank you for the quick reply! But the solution provided by you, it seems, has still not been able to address my issue. I ran the program at command prompt with your said parameters, but the download still gave an error in the App window.
Also, is there some way of defining these parameters in the source code? I am keen in using NetBeans to run the program.
Cheers!