Example 5.6 is an improved version of the URLViewer you first encountered in Chapter 2. This is a simple application that provides a window in which you can view the contents of a URL. It assumes that those contents are more or less ASCII text. (In future chapters, I’ll remove that restriction.) Figure 5.1 shows the result. Our application has a text area in which the user can type a URL, a Load button that the user uses to load the specified URL, and a StreamedTextArea component that displays the text from the URL. Each of these corresponds to a field in the URLViewer class.

Figure 5-1. The URLViewer

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import com.macfaq.awt.*;
import com.macfaq.io.*;

public class URLViewer extends Frame 
 implements WindowListener, ActionListener {

  TextField theURL = new TextField();
  Button loadButton = new Button("Load");
  StreamedTextArea theDisplay = new StreamedTextArea();
  
  public URLViewer() {
    super("URL Viewer");
  }

  public void init() {
  
    this.add("North", theURL);
    this.add("Center", theDisplay);
    Panel south = new Panel();
    south.add(loadButton);
    this.add("South", south);
    theURL.addActionListener(this);
    loadButton.addActionListener(this);
    this.addWindowListener(this);
    this.setLocation(50, 50);
    this.pack();
    this.show();
  }

  public void actionPerformed(ActionEvent evt) {
  
    try {
      URL u = new URL(theURL.getText());
      InputStream in = u.openStream();
      OutputStream out = theDisplay.getOutputStream();
      StreamCopier.copy(in, out);
      in.close();
      out.close();
    }
    catch (MalformedURLException ex) {theDisplay.setText("Invalid URL");}
    catch (IOException ex) {theDisplay.setText("Invalid URL");}
  }
  
  public void windowClosing(WindowEvent e) {
  
    this.setVisible(false);
    this.dispose();
  }
  
  public void windowOpened(WindowEvent e) {}
  public void windowClosed(WindowEvent e) {}
  public void windowIconified(WindowEvent e) {}
  public void windowDeiconified(WindowEvent e) {}
  public void windowActivated(WindowEvent e) {}
  public void windowDeactivated(WindowEvent e) {}

  public static void main(String args[]) {

    URLViewer me = new URLViewer();
    me.init();
  }
}

The URLViewer class itself extends Frame. An alternative would have been to extend Panel, which would have allowed URLViewer objects to be embedded in other containers. However, this application seemed big enough to justify exclusive use of a window. URLViewer implements the WindowListener interface to enable the user to close the window by clicking in the close box. Only the windowClosing() method is nontrivial. The other six window methods are do-nothing methods required to satisfy the contract of the WindowListener interface.

The init() method builds the interface and displays the window. This is invoked by the main() method, which constructs a new URLViewer object. The constructor is quite simple, merely passing the title of the frame to the superclass constructor.

The streamed text area is filled when the user clicks the Load button or hits Return inside the URL text field. The URLViewer object listens to both of these components. The URLViewer’s actionPerformed() method constructs a URL from the text in the text field, then opens an input stream from the URL in the text field. Next, StreamCopier from Chapter 3 pours the data from the URL’s input stream into the text area’s output stream. When that’s finished, both streams are closed.