FileViewer.java Source code

Introduction

Here is the source code for FileViewer.java

Source

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
 */

import java.awt.Button;
import java.awt.FileDialog;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.Frame;
import java.awt.Panel;
import java.awt.TextArea;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

/**
 * This class creates and displays a window containing a TextArea, in which the
 * contents of a text file are displayed.
 */
public class FileViewer extends Frame implements ActionListener {
    String directory; // The default directory to display in the FileDialog

    TextArea textarea; // The area to display the file contents into

    /** Convenience constructor: file viewer starts out blank */
    public FileViewer() {
        this(null, null);
    }

    /** Convenience constructor: display file from current directory */
    public FileViewer(String filename) {
        this(null, filename);
    }

    /**
     * The real constructor. Create a FileViewer object to display the specified
     * file from the specified directory
     */
    public FileViewer(String directory, String filename) {
        super(); // Create the frame

        // Destroy the window when the user requests it
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                dispose();
            }
        });

        // Create a TextArea to display the contents of the file in
        textarea = new TextArea("", 24, 80);
        textarea.setFont(new Font("MonoSpaced", Font.PLAIN, 12));
        textarea.setEditable(false);
        this.add("Center", textarea);

        // Create a bottom panel to hold a couple of buttons in
        Panel p = new Panel();
        p.setLayout(new FlowLayout(FlowLayout.RIGHT, 10, 5));
        this.add(p, "South");

        // Create the buttons and arrange to handle button clicks
        Font font = new Font("SansSerif", Font.BOLD, 14);
        Button openfile = new Button("Open File");
        Button close = new Button("Close");
        openfile.addActionListener(this);
        openfile.setActionCommand("open");
        openfile.setFont(font);
        close.addActionListener(this);
        close.setActionCommand("close");
        close.setFont(font);
        p.add(openfile);
        p.add(close);

        this.pack();

        // Figure out the directory, from filename or current dir, if necessary
        if (directory == null) {
            File f;
            if ((filename != null) && (f = new File(filename)).isAbsolute()) {
                directory = f.getParent();
                filename = f.getName();
            } else
                directory = System.getProperty("user.dir");
        }

        this.directory = directory; // Remember the directory, for FileDialog
        setFile(directory, filename); // Now load and display the file
    }

    /**
     * Load and display the specified file from the specified directory
     */
    public void setFile(String directory, String filename) {
        if ((filename == null) || (filename.length() == 0))
            return;
        File f;
        FileReader in = null;
        // Read and display the file contents. Since we're reading text, we
        // use a FileReader instead of a FileInputStream.
        try {
            f = new File(directory, filename); // Create a file object
            in = new FileReader(f); // And a char stream to read it
            char[] buffer = new char[4096]; // Read 4K characters at a time
            int len; // How many chars read each time
            textarea.setText(""); // Clear the text area
            while ((len = in.read(buffer)) != -1) { // Read a batch of chars
                String s = new String(buffer, 0, len); // Convert to a string
                textarea.append(s); // And display them
            }
            this.setTitle("FileViewer: " + filename); // Set the window title
            textarea.setCaretPosition(0); // Go to start of file
        }
        // Display messages if something goes wrong
        catch (IOException e) {
            textarea.setText(e.getClass().getName() + ": " + e.getMessage());
            this.setTitle("FileViewer: " + filename + ": I/O Exception");
        }
        // Always be sure to close the input stream!
        finally {
            try {
                if (in != null)
                    in.close();
            } catch (IOException e) {
            }
        }
    }

    /**
     * Handle button clicks
     */
    public void actionPerformed(ActionEvent e) {
        String cmd = e.getActionCommand();
        if (cmd.equals("open")) { // If user clicked "Open" button
            // Create a file dialog box to prompt for a new file to display
            FileDialog f = new FileDialog(this, "Open File", FileDialog.LOAD);
            f.setDirectory(directory); // Set the default directory

            // Display the dialog and wait for the user's response
            f.show();

            directory = f.getDirectory(); // Remember new default directory
            setFile(directory, f.getFile()); // Load and display selection
            f.dispose(); // Get rid of the dialog box
        } else if (cmd.equals("close")) // If user clicked "Close" button
            this.dispose(); // then close the window
    }

    /**
     * The FileViewer can be used by other classes, or it can be used standalone
     * with this main() method.
     */
    static public void main(String[] args) throws IOException {
        // Create a FileViewer object
        Frame f = new FileViewer((args.length == 1) ? args[0] : null);
        // Arrange to exit when the FileViewer window closes
        f.addWindowListener(new WindowAdapter() {
            public void windowClosed(WindowEvent e) {
                System.exit(0);
            }
        });
        // And pop the window up
        f.show();
    }
}