downloadfiles.java

< ProJavaProgrammingSecondEdition> 书中例程源码

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

public class DownloadFiles extends JPanel {

  protected JPanel listPanel;
  protected GridBagConstraints constraints;

  public static void main(String[] args) {
    JFrame f = new JFrame("Download Files");
    DownloadFiles df = new DownloadFiles();
    for (int i = 0; i < args.length; i++) {
      df.createDownloader(args[i]);
    }
    f.getContentPane().add(df);
    f.setSize(600, 400);
    f.setVisible(true);
  }

  public DownloadFiles() {
    setLayout(new BorderLayout());
    listPanel = new JPanel();
    listPanel.setLayout(new GridBagLayout());
    constraints = new GridBagConstraints();
    constraints.gridx = 0;
    constraints.weightx = 1;
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.anchor = GridBagConstraints.NORTH;
    JScrollPane jsp = new JScrollPane(listPanel);
    add(jsp, BorderLayout.CENTER);

    add(getAddURLPanel(), BorderLayout.SOUTH);
  }

  protected JPanel getAddURLPanel() {
    JPanel panel = new JPanel();
    JLabel label = new JLabel("URL:");
    final JTextField textField = new JTextField(20);
    JButton downloadButton = new JButton("Download");
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        if (createDownloader(textField.getText())) {
          textField.setText("");
          revalidate();
        }
      }
    };
    textField.addActionListener(actionListener);
    downloadButton.addActionListener(actionListener);
    JButton clearAll = new JButton("Cancel All");
    clearAll.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        Downloader.cancelAllAndWait();
        listPanel.removeAll();
        revalidate();
        repaint();
      }
    });
    panel.add(label);
    panel.add(textField);
    panel.add(downloadButton);
    return panel;
  }

  protected boolean createDownloader(String url) {
    try {
      URL downloadURL = new URL(url);
      URLConnection urlConn = downloadURL.openConnection();
      int length = urlConn.getContentLength();
      if (length < 0) throw new Exception(
          "Unable to determine content " +
          "length for '" + url + "'");
      int index = url.lastIndexOf('/');
      FileOutputStream fos = new FileOutputStream(
          url.substring(index + 1));
      BufferedOutputStream bos =
          new BufferedOutputStream(fos);
      DownloadManager dm = new DownloadManager(
          downloadURL, bos);
      listPanel.add(dm, constraints);
      return true;
    }
    catch (Exception e) {
      JOptionPane.showMessageDialog(this, e.getMessage(),
          "Unable To Download",
          JOptionPane.ERROR_MESSAGE);
    }
    return false;
  }
 
}