mybufferedinputstream.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 MyBufferedInputStream extends FilterInputStream {
  public MyBufferedInputStream (InputStream in) {
    this (in, 512);
  }
  
  protected byte[] buffer;
  protected int bufferSize, bufferIndex, bufferCapacity;
  
  public MyBufferedInputStream (InputStream in, int bufferCapacity) {
    super (in);
    this.bufferCapacity = bufferCapacity;
    buffer = new byte[bufferCapacity];
  }

  public synchronized int available () throws IOException {
    return (bufferSize < 0) ? 0 :
      (bufferIndex < bufferSize) ? bufferSize - bufferIndex : in.available ();
  }

  public synchronized int read () throws IOException {
    if (bufferIndex >= bufferSize) {
      if (bufferSize < 0)
        return -1;
      fillBuffer ();
      if (bufferSize < 0)
        return -1;
    }
    return buffer[bufferIndex ++] & 0xff;
  }

  protected void fillBuffer () throws IOException {
    bufferIndex = 0;
    bufferSize = in.read (buffer, 0, bufferCapacity);
  }

  public synchronized int read (byte[] data, int offset, int length) throws IOException {
    int amount;
    if (length <= 0) {
      amount = 0;
    } else if (bufferIndex < bufferSize) {
      amount = Math.min (length, bufferSize - bufferIndex);
      System.arraycopy (buffer, bufferIndex, data, offset, amount);
      bufferIndex += amount;
    } else {
      if (bufferSize < 0)
        return -1;
      if (length < bufferCapacity) {
        fillBuffer ();
        amount = read (data, offset, length);
      } else {
        amount = in.read (data, offset, length);
        if (amount < 0)
          bufferSize = -1;
      }
    }
    return amount;
  }

  public synchronized long skip (long amount) throws IOException {
    if ((amount <= 0) || (bufferSize < 0)) {
      return 0;
    } else if (bufferIndex < bufferSize) {
      int skip = (int) Math.min (amount, bufferSize - bufferIndex);
      bufferIndex += skip;
      return skip;
    } else {
      return in.skip (amount);
    }
  }
}