htmllinkfinder.java

书籍"Java_面向事件编程"的附带光盘代码

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

// A class that allows one to fetch an HTML file from the web and obtain
// a list of all the links contained within the HTML.
public class HTMLLinkFinder
    extends JFrame
    implements ActionListener, ItemListener {
    
    // dimensions of the window
    private static final int WINDOW_WIDTH = 800;
    private static final int WINDOW_HEIGHT = 550;
    
    // Width of area for URL entry
    private static final int URLFIELDWIDTH = 60;
    
    // Dimensions for HTML display area
    private static final int HTMLWIDTH = 60;
    private static final int HTMLHEIGHT = 14;
    
    // Dimensions for links display area
    private static final int LINKSWIDTH = 60;
    private static final int LINKSHEIGHT = 10;
    
    // Large font for GUI controls
    private Font bigFont = new Font("Times", Font.PLAIN, 16);
    
    // Area in which HTML is displayed
    private JTextArea html;
    
    // Link display area
    private JTextArea links;
    
    // The "load" button
    private JButton doit;
    
    // Url controls
    private JTextField urlName;
    private JComboBox favorites;
    
    // Set up all GUI controls and their listeners
    public void begin() {
        
        Container pane = getContentPane();
        pane.setLayout(new FlowLayout());
        
        // Create a "bookmarks" menu
        pane.add(new JLabel("Favorites:"));
        favorites = new JComboBox();
        favorites.setFont(bigFont);
        favorites.addItem("http://java.sun.com");
        favorites.addItem("http://www.apple.com");
        favorites.addItem("http://www.cnn.com");
        favorites.addItemListener(this);
        pane.add(favorites);
        
        // Create a text area into which a URL may be entered
        urlName = new JTextField("Enter URL", URLFIELDWIDTH);
        urlName.setFont(bigFont);
        pane.add(urlName);
        
        // Create the button used to start fetching a web page
        doit = new JButton("Fetch HTML");
        doit.setFont(bigFont);
        doit.addActionListener(this);
        pane.add(doit);
        
        // Create the text areas in which HTML and links will be displayed.
        html = new JTextArea(HTMLHEIGHT, HTMLWIDTH);
        html.setFont(bigFont);
        pane.add(new JScrollPane(html));
        
        links = new JTextArea(LINKSHEIGHT, LINKSWIDTH);
        links.setFont(bigFont);
        pane.add(new JScrollPane(links));

        validate();
        
    }
    
    // If item is selected from "favorites" menu, enter it as current URL
    public void itemStateChanged(ItemEvent e) {
        urlName.setText(favorites.getSelectedItem().toString());
    }
    
    // Fetch the web page at "urlString" and return its contents as a String
    private String getWebPage(String urlString) {
        String page = "";
        try {
            URL url = new URL(urlString);
            BufferedReader input =
                new BufferedReader(new InputStreamReader(url.openStream()));
            
            String line = input.readLine();
            while (line != null) {
                page = page + line + "\n";
                line = input.readLine();
            }
            
            input.close();
            
        } catch (Exception ex) {
            JOptionPane.showMessageDialog(this, ex);
        }
        return page;
    }
    
    // Extract all the links from a web page
    private String findLinks(String fullpage) {
        
        int tagPos, // Start of <A tag specification
            tagEnd; // Position of first ">" after tag start
        
        // A lower case only version of the page for searching
        String lowerpage = fullpage.toLowerCase();
        
        // Text of one A tag
        String tag;
        
        // The A tags found so far
        String links = "";
        
        // Paste stuff on end of page to ensure searches succeed
        fullpage = fullpage + " >";
        
        tagPos = lowerpage.indexOf("<a ", 0);
        
        while (tagPos >= 0) {
            tagEnd = fullpage.indexOf(">", tagPos + 1);
            tag = fullpage.substring(tagPos, tagEnd + 1);
            links = links + tag + "\n";
            tagPos = lowerpage.indexOf("<a ", tagEnd);
        }
        
        return links;
    }
    
    // When the "Fetch" button is pressed, try to get the HTML, display and search it.
    public void actionPerformed(ActionEvent e) {
        String fullpage;
        String url;
        
        if (links.getSelectedText() != null) {
            urlName.setText(links.getSelectedText().trim());
        }
        
        url = urlName.getText();
        fullpage = getWebPage(url);
        html.setText(fullpage);
        links.setText(findLinks(fullpage));
    }
    
    public static void main ( String[] args ) {
        HTMLLinkFinder self = new HTMLLinkFinder();

        self.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
        self.setTitle("HTML Link Finder");

        self.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        self.setVisible(true);

        self.begin();
    }
    
}