package net.codejava.swing.download;
 
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
 
/**
 * A utility that downloads a file from a URL.
 * @author www.codejava.net
 */
public class HTTPDownloadUtil {
 
    private HttpURLConnection httpConn;
 
    /**
     * hold input stream of HttpURLConnection
     */
    private InputStream inputStream;
 
    private String fileName;
    private int contentLength;
 
    /**
     * Downloads a file from a URL
     *
     * @param fileURL
     *            HTTP URL of the file to be downloaded
     * @throws IOException
     */
    public void downloadFile(String fileURL) throws IOException {
        URL url = new URL(fileURL);
        httpConn = (HttpURLConnection) url.openConnection();
        int responseCode = httpConn.getResponseCode();
 
        // always check HTTP response code first
        if (responseCode == HttpURLConnection.HTTP_OK) {
            String disposition = httpConn.getHeaderField("Content-Disposition");
            String contentType = httpConn.getContentType();
            contentLength = httpConn.getContentLength();
 
            if (disposition != null) {
                // extracts file name from header field
                int index = disposition.indexOf("filename=");
                if (index > 0) {
                    fileName = disposition.substring(index + 10,
                            disposition.length() - 1);
                }
            } else {
                // extracts file name from URL
                fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1,
                        fileURL.length());
            }
 
            // output for debugging purpose only
            System.out.println("Content-Type = " + contentType);
            System.out.println("Content-Disposition = " + disposition);
            System.out.println("Content-Length = " + contentLength);
            System.out.println("fileName = " + fileName);
 
            // opens input stream from the HTTP connection
            inputStream = httpConn.getInputStream();
 
        } else {
            throw new IOException(
                    "No file to download. Server replied HTTP code: "
                            + responseCode);
        }
    }
 
    public void disconnect() throws IOException {
        inputStream.close();
        httpConn.disconnect();
    }
 
    public String getFileName() {
        return this.fileName;
    }
 
    public int getContentLength() {
        return this.contentLength;
    }
 
    public InputStream getInputStream() {
        return this.inputStream;
    }
}

package net.codejava.swing.download;
 
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
 
import javax.swing.JOptionPane;
import javax.swing.SwingWorker;
 
/**
 * Execute file download in a background thread and update the progress.
 * @author www.codejava.net
 *
 */
public class DownloadTask extends SwingWorker<Void, Void> {
    private static final int BUFFER_SIZE = 4096;  
    private String downloadURL;
    private String saveDirectory;
    private SwingFileDownloadHTTP gui;
     
    public DownloadTask(SwingFileDownloadHTTP gui, String downloadURL, String saveDirectory) {
        this.gui = gui;
        this.downloadURL = downloadURL;
        this.saveDirectory = saveDirectory;
    }
     
    /**
     * Executed in background thread
     */
    @Override
    protected Void doInBackground() throws Exception {
        try {
            HTTPDownloadUtil util = new HTTPDownloadUtil();
            util.downloadFile(downloadURL);
             
            // set file information on the GUI
            gui.setFileInfo(util.getFileName(), util.getContentLength());
             
            String saveFilePath = saveDirectory + File.separator + util.getFileName();
 
            InputStream inputStream = util.getInputStream();
            // opens an output stream to save into file
            FileOutputStream outputStream = new FileOutputStream(saveFilePath);
 
            byte[] buffer = new byte[BUFFER_SIZE];
            int bytesRead = -1;
            long totalBytesRead = 0;
            int percentCompleted = 0;
            long fileSize = util.getContentLength();
 
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
                totalBytesRead += bytesRead;
                percentCompleted = (int) (totalBytesRead * 100 / fileSize);
 
                setProgress(percentCompleted);        
            }
 
            outputStream.close();
 
            util.disconnect();
        } catch (IOException ex) {
            JOptionPane.showMessageDialog(gui, "Error downloading file: " + ex.getMessage(),
                    "Error", JOptionPane.ERROR_MESSAGE);          
            ex.printStackTrace();
            setProgress(0);
            cancel(true);          
        }
        return null;
    }
 
    /**
     * Executed in Swing's event dispatching thread
     */
    @Override
    protected void done() {
        if (!isCancelled()) {
            JOptionPane.showMessageDialog(gui,
                    "File has been downloaded successfully!", "Message",
                    JOptionPane.INFORMATION_MESSAGE);
        }
    }  
}

package net.codejava.swing.download;
 
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
 
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JProgressBar;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
 
import net.codejava.swing.JFilePicker;
 
/**
 * A Swing application that downloads file from an HTTP server.
 * @author www.codejava.net
 *
 */
public class SwingFileDownloadHTTP extends JFrame implements
        PropertyChangeListener {
    private JLabel labelURL = new JLabel("Download URL: ");
    private JTextField fieldURL = new JTextField(30);
 
    private JFilePicker filePicker = new JFilePicker("Save in directory: ",
            "Browse...");
 
    private JButton buttonDownload = new JButton("Download");
 
    private JLabel labelFileName = new JLabel("File name: ");
    private JTextField fieldFileName = new JTextField(20);
     
    private JLabel labelFileSize = new JLabel("File size (bytes): ");
    private JTextField fieldFileSize = new JTextField(20);
     
    private JLabel labelProgress = new JLabel("Progress:");
    private JProgressBar progressBar = new JProgressBar(0, 100);
     
    public SwingFileDownloadHTTP() {
        super("Swing File Download from HTTP server");
 
        // set up layout
        setLayout(new GridBagLayout());
        GridBagConstraints constraints = new GridBagConstraints();
        constraints.anchor = GridBagConstraints.WEST;
        constraints.insets = new Insets(5, 5, 5, 5);
 
        // set up components
        filePicker.setMode(JFilePicker.MODE_SAVE);
        filePicker.getFileChooser().setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
 
        buttonDownload.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                buttonDownloadActionPerformed(event);
            }
        });
 
        fieldFileName.setEditable(false);
        fieldFileSize.setEditable(false);
         
        progressBar.setPreferredSize(new Dimension(200, 30));
        progressBar.setStringPainted(true);
 
        // add components to the frame
        constraints.gridx = 0;
        constraints.gridy = 0;
        add(labelURL, constraints);
 
        constraints.gridx = 1;
        constraints.fill = GridBagConstraints.HORIZONTAL;
        constraints.weightx = 1.0;
        add(fieldURL, constraints);
 
        constraints.gridx = 0;
        constraints.gridy = 1;
        constraints.weightx = 0.0;
        constraints.gridwidth = 2;
        constraints.fill = GridBagConstraints.NONE;
        add(filePicker, constraints);
 
        constraints.gridy = 2;
        constraints.anchor = GridBagConstraints.CENTER;
        add(buttonDownload, constraints);
         
        constraints.gridx = 0;
        constraints.gridy = 3;
        constraints.gridwidth = 1;
        constraints.anchor = GridBagConstraints.WEST;
        add(labelFileName, constraints);
         
        constraints.gridx = 1;
        add(fieldFileName, constraints);
         
        constraints.gridy = 4;
        constraints.gridx = 0;
        add(labelFileSize, constraints);
         
        constraints.gridx = 1;
        add(fieldFileSize, constraints);
         
        constraints.gridx = 0;
        constraints.gridy = 5;
        constraints.gridwidth = 1;
        constraints.anchor = GridBagConstraints.WEST;
        add(labelProgress, constraints);
 
        constraints.gridx = 1;
        constraints.weightx = 1.0;
        constraints.fill = GridBagConstraints.HORIZONTAL;
        add(progressBar, constraints);
 
        pack();
        setLocationRelativeTo(null);    // center on screen
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    
    }
 
    /**
     * handle click event of the Upload button
     */
    private void buttonDownloadActionPerformed(ActionEvent event) {
        String downloadURL = fieldURL.getText();
        String saveDir = filePicker.getSelectedFilePath();
 
        // validate input first
        if (downloadURL.equals("")) {
            JOptionPane.showMessageDialog(this, "Please enter download URL!",
                    "Error", JOptionPane.ERROR_MESSAGE);
            fieldURL.requestFocus();
            return;
        }
 
        if (saveDir.equals("")) {
            JOptionPane.showMessageDialog(this,
                    "Please choose a directory save file!", "Error",
                    JOptionPane.ERROR_MESSAGE);
            return;
        }
 
        try {
            progressBar.setValue(0);
 
            DownloadTask task = new DownloadTask(this, downloadURL, saveDir);
            task.addPropertyChangeListener(this);
            task.execute();
        } catch (Exception ex) {
            JOptionPane.showMessageDialog(this,
                    "Error executing upload task: " + ex.getMessage(), "Error",
                    JOptionPane.ERROR_MESSAGE);
        }      
    }
 
    void setFileInfo(String name, int size) {
        fieldFileName.setText(name);
        fieldFileSize.setText(String.valueOf(size));
    }
     
    /**
     * Update the progress bar's state whenever the progress of download changes.
     */
    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        if (evt.getPropertyName().equals("progress")) {
            int progress = (Integer) evt.getNewValue();
            progressBar.setValue(progress);
        }
    }
     
    /**
     * Launch the application
     */
    public static void main(String[] args) {
        try {
            // set look and feel to system dependent
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception ex) {
            ex.printStackTrace();
        }
 
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new SwingFileDownloadHTTP().setVisible(true);
            }
        });
    }  
}