Text file viewer : FileReader « File Input Output « Java

Text file viewer

Text file viewer
 * 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) {

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


    // 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))
    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)
      } 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

      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) {
    // And pop the window up


Related examples in the same category

1.Create BufferedReader from FileReader and process lines from file
2.Read characters with FileReader
3.Read and copy with FileReader and FileWriter
4.Use FileReader and FileWriter
5.An InputStream backed by a Reader
6.Text File Test