SimpleWebBrowser.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.HyperlinkEvent;
import javax.swing.event.HyperlinkListener;
import java.net.URL;

/**
 * Defines a simple web browser that can load web pages from
 * URLs specified by the user in a "Location" box.  Almost all
 * the functionality is provided automatically by the JEditorPane
 * class.  The program loads web pages synchronously and can hang
 * indefinitely while trying to load a page.  See
 * SimpleWebBrowserWithThread for an asynchronous version.
 * This class can be run as a standalone application.
 */
public class SimpleWebBrowser extends JPanel {

	/**
	 * The main routine simply opens a window that shows a SimpleWebBrowser panel.
	 */
	public static void main(String[] args) {
		JFrame window = new JFrame("SimpleWebBrowser");
		SimpleWebBrowser content = new SimpleWebBrowser();
		window.setContentPane(content);
		window.setSize(600,500);
		Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
		window.setLocation( (screenSize.width - window.getWidth())/2,
				(screenSize.height - window.getHeight())/2 );
		window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
		window.setVisible(true);
	}
	
		
	/**
	 * The pane in which documents are displayed.
	 */
	private JEditorPane editPane;
	
	
	/**
	 * An input box where the user enters the URL of a document
	 * to be loaded into the edit pane.  A valid URL string has
	 * to contain the substring "://".  If the string in the box
	 * does not contain this substring, then "http://" is 
	 * prepended to the string.
	 */
	private JTextField locationInput;
	
	
	/**
	 * Defines a listener that responds when the user clicks on
	 * a link in the document.
	 */
	private class LinkListener implements HyperlinkListener {
		public void hyperlinkUpdate(HyperlinkEvent evt) {
			if (evt.getEventType() == HyperlinkEvent.EventType.ACTIVATED) {
				loadURL(evt.getURL());
			}
		}
	}
	
	
	/**
	 * Defines a listener that loads a new page when the user
	 * clicks the "Go" button or presses return in the location
	 * input box.
	 */
	private class GoListener implements ActionListener {
		public void actionPerformed(ActionEvent evt) {
			URL url;
			try {
				String location = locationInput.getText().trim();
				if (location.length() == 0)
					throw new Exception();
				if (! location.contains("://"))
					location = "http://" + location;
				url = new URL(location);
			}
			catch (Exception e) {
				JOptionPane.showMessageDialog(SimpleWebBrowser.this, 
						"The Location input box does not\ncontain a legal URL.");
				return;
			}
			loadURL(url);
			locationInput.selectAll();
			locationInput.requestFocus();
		}
	}

	
	/**
	 * Construct a panel that contains a JEditorPane in a JScrollPane,
	 * with a tool bar that has a Location input box and a Go button.
	 */
	public SimpleWebBrowser() {
		
		setBackground(Color.BLACK);
		setLayout(new BorderLayout(1,1));
		setBorder(BorderFactory.createLineBorder(Color.BLACK,1));

		editPane = new JEditorPane();
		editPane.setEditable(false);
		editPane.addHyperlinkListener(new LinkListener());
		add(new JScrollPane(editPane),BorderLayout.CENTER);
		
		JToolBar toolbar = new JToolBar();
		toolbar.setFloatable(false);
		add(toolbar,BorderLayout.NORTH);
		ActionListener goListener = new GoListener();
		locationInput = new JTextField("math.hws.edu/javanotes/index.html", 40);
		locationInput.addActionListener(goListener);
		JButton goButton = new JButton(" Go ");
		goButton.addActionListener(goListener);
		toolbar.add( new JLabel(" Location: "));
		toolbar.add(locationInput);
		toolbar.addSeparator(new Dimension(5,0));
		toolbar.add(goButton);

	}
	
	
	/**
	 * Loads the document at the specified URL into the edit pane.
	 */
	private void loadURL(URL url) {
		try {
			editPane.setPage(url);
		}
		catch (Exception e) {
			editPane.setContentType("text/plain");
			editPane.setText( "Sorry, the requested document was not found\n"
					+"or cannot be displayed.\n\nError:" + e);
		}
	}
	
}