markresetfileinputstream.java

JAVA网络编程技术内幕一书的源代码

/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved; see license.txt for details.
 */

import java.io.*;

public class MarkResetFileInputStream extends FileInputStream {
  public MarkResetFileInputStream (String filename) throws IOException {
    this (new RandomAccessFile (filename, "r"));
  }

  public MarkResetFileInputStream (File file) throws IOException {
    this (file.getPath ());
  }

  protected long markedPosition;
  protected RandomAccessFile file;
  
  protected MarkResetFileInputStream (RandomAccessFile file) throws IOException {
    super (file.getFD ());
    this.file = file;
    markedPosition = -1;
  }

  public boolean markSupported () {
    return true;
  }

  public void mark (int readAheadLimit) {
    try {
      markedPosition = file.getFilePointer ();
    } catch (IOException ex) {
      markedPosition = -1;
    }
  }
  
  public void reset () throws IOException {
    if (markedPosition == -1)
      throw new IOException ("No mark set.");
    file.seek (markedPosition);
  }
}