Java/File Input Output/FileReader

An InputStream backed by a Reader

 

/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.ru/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE ABOVE NAMED AUTHORS "AS IS" AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS, THEIR
 * PUBLISHER OR THEIR EMPLOYERS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
/**
 * An InputStream backed by a Reader
 */
public class ReaderInputStream extends InputStream {
  protected Reader reader;
  protected ByteArrayOutputStream byteArrayOut;
  protected Writer writer;
  protected char[] chars;
  protected byte[] buffer;
  protected int index, length;
  /**
   * Constructor to supply a Reader
   *
   * @param reader - the Reader used by the InputStream
   */
  public ReaderInputStream(Reader reader) {
    this.reader = reader;
    byteArrayOut = new ByteArrayOutputStream();
    writer = new OutputStreamWriter(byteArrayOut);
    chars = new char[1024];
  }
  /**
   * Constructor to supply a Reader and an encoding
   *
   * @param reader   - the Reader used by the InputStream
   * @param encoding - the encoding to use for the InputStream
   * @throws UnsupportedEncodingException if the encoding is not supported
   */
  public ReaderInputStream(Reader reader, String encoding) throws UnsupportedEncodingException {
    this.reader = reader;
    byteArrayOut = new ByteArrayOutputStream();
    writer = new OutputStreamWriter(byteArrayOut, encoding);
    chars = new char[1024];
  }
  /**
   * @see java.io.InputStream#read()
   */
  public int read() throws IOException {
    if (index >= length)
      fillBuffer();
    if (index >= length)
      return -1;
    return 0xff & buffer[index++];
  }
  protected void fillBuffer() throws IOException {
    if (length < 0)
      return;
    int numChars = reader.read(chars);
    if (numChars < 0) {
      length = -1;
    } else {
      byteArrayOut.reset();
      writer.write(chars, 0, numChars);
      writer.flush();
      buffer = byteArrayOut.toByteArray();
      length = buffer.length;
      index = 0;
    }
  }
  /**
   * @see java.io.InputStream#read(byte[], int, int)
   */
  public int read(byte[] data, int off, int len) throws IOException {
    if (index >= length)
      fillBuffer();
    if (index >= length)
      return -1;
    int amount = Math.min(len, length - index);
    System.arraycopy(buffer, index, data, off, amount);
    index += amount;
    return amount;
  }
  /**
   * @see java.io.InputStream#available()
   */
  public int available() throws IOException {
    return (index < length) ? length - index :
        ((length >= 0) && reader.ready()) ? 1 : 0;
  }
  /**
   * @see java.io.InputStream#close()
   */
  public void close() throws IOException {
    reader.close();
  }
}

Create BufferedReader from FileReader and process lines from file

 
import java.io.BufferedReader;
import java.io.FileReader;
class Main {
  public static void main(String args[]) throws Exception {
    FileReader fr = new FileReader(args[0]);
    BufferedReader br = new BufferedReader(fr);
    // Process lines from file
    String line;
    while ((line = br.readLine()) != null) {
      char array[] = line.toCharArray();
      System.out.print(array[0]);
    }
  }
}

Read and copy with FileReader and FileWriter

 
import java.io.FileReader;
import java.io.FileWriter;
import java.io.Reader;
import java.io.Writer;
public class FileReaderWriterExample {
  public static void main(String[] args) throws Exception {
    Reader r = new FileReader("in.txt");
    Writer w = new FileWriter("out.txt");
    int c;
    while ((c = r.read()) != -1) {
      System.out.print((char) c);
      w.write(c);
    }
    r.close();
    w.close();
  }
}

Read characters with FileReader

 
import java.io.FileReader;
class DigitCounter {
  public static void main(String args[]) throws Exception {
    // Create a file reader
    FileReader fr = new FileReader(args[0]);
    // Read characters
    int i;
    while ((i = fr.read()) != -1) {
      System.out.println((char) i);
    }
    // Close file reader
    fr.close();
  }
}

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.ru/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();
  }
}

Use FileReader and FileWriter

 
/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class Copy {
  public static void main(String[] args) throws IOException {
    File inputFile = new File("farrago.txt");
    File outputFile = new File("outagain.txt");
    FileReader in = new FileReader(inputFile);
    FileWriter out = new FileWriter(outputFile);
    int c;
    while ((c = in.read()) != -1)
      out.write(c);
    in.close();
    out.close();
  }
}