siteselector.java

This program uses a button to load a document from a URL

// Fig. 18.2: SiteSelector.java
// This program uses a button to load a document from a URL.
import java.net.*;
import java.util.*;
import java.awt.*;
import java.applet.AppletContext;
import javax.swing.*;
import javax.swing.event.*;

public class SiteSelector extends JApplet {
   private HashMap sites;    // site names and URLs
   private Vector siteNames;   // site names
   private JList siteChooser;  // list of sites to choose from

   // read HTML parameters and set up GUI
   public void init()
   {
      // create HashMap and Vector
      sites = new HashMap();
      siteNames = new Vector();

      // obtain parameters from HTML document
      getSitesFromHTMLParameters();

      // create GUI components and layout interface
      Container container = getContentPane();
      container.add( new JLabel( "Choose a site to browse" ),
         BorderLayout.NORTH );

      siteChooser = new JList( siteNames );
      siteChooser.addListSelectionListener(

         new ListSelectionListener() {

            // go to site user selected
            public void valueChanged( ListSelectionEvent event )
            {
               // get selected site name
               Object object = siteChooser.getSelectedValue();

               // use site name to locate corresponding URL
               URL newDocument = ( URL ) sites.get( object );

               // get reference to applet container
               AppletContext browser = getAppletContext();

               // tell applet container to change pages
               browser.showDocument( newDocument );
            }

         } // end inner class

      ); // end call to addListSelectionListener

      container.add( new JScrollPane( siteChooser ), 
         BorderLayout.CENTER );

   } // end method init

   // obtain parameters from HTML document
   private void getSitesFromHTMLParameters()
   {
      // look for applet parameters in HTML document and add to HashMap
      String title, location;
      URL url;
      int counter = 0;

      title = getParameter( "title" + counter ); // get first site title

      // loop until no more parameters in HTML document
      while ( title != null ) {

         // obtain site location
         location = getParameter( "location" + counter );
            
         // place title/URL in HashMap and title in Vector
         try {
            url = new URL( location ); // convert location to URL
            sites.put( title, url );   // put title/URL in HashMap
            siteNames.add( title );    // put title in Vector
         }

         // process invalid URL format
         catch ( MalformedURLException urlException ) {
            urlException.printStackTrace();
         }

         ++counter;  
         title = getParameter( "title" + counter ); // get next site title

      } // end while

   } // end method getSitesFromHTMLParameters

} // end class SiteSelector

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 * (C) Copyright 1992-2003 by Deitel & Associates, Inc. and               *
 * Prentice Hall. All Rights Reserved.                                    *
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