inputstream.java

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package org.apache.lucene.store;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
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 * 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.
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 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
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 * 5. Products derived from this software may not be called "Apache",
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.io.IOException;

/**
  Abstract class for input from a file in a Directory.
  @author Doug Cutting
*/

/** A random-access input stream */
abstract public class InputStream implements Cloneable {
  final static int BUFFER_SIZE = OutputStream.BUFFER_SIZE;

  private byte[] buffer;
  private char[] chars;

  private long bufferStart = 0;			  // position in file of buffer
  private int bufferLength = 0;			  // end of valid bytes
  private int bufferPosition = 0;		  // next byte to read

  protected long length;			  // set by subclasses

  /** InputStream-like methods @see java.io.InputStream */
  public final byte readByte() throws IOException {
    if (bufferPosition >= bufferLength)
      refill();
    return buffer[bufferPosition++];
  }

  public final void readBytes(byte[] b, int offset, int len)
       throws IOException {
    if (len < BUFFER_SIZE) {
      for (int i = 0; i < len; i++)		  // read byte-by-byte
	b[i + offset] = (byte)readByte();
    } else {					  // read all-at-once
      long start = getFilePointer();
      seekInternal(start);
      readInternal(b, offset, len);

      bufferStart = start + len;		  // adjust stream variables
      bufferPosition = 0;
      bufferLength = 0;				  // trigger refill() on read
    }
  }

  public final int readInt() throws IOException {
    return ((readByte() & 0xFF) << 24) | ((readByte() & 0xFF) << 16)
         | ((readByte() & 0xFF) <<  8) |  (readByte() & 0xFF);
  }

  public final int readVInt() throws IOException {
    byte b = readByte();
    int i = b & 0x7F;
    for (int shift = 7; (b & 0x80) != 0; shift += 7) {
      b = readByte();
      i |= (b & 0x7F) << shift;
    }
    return i;
  }

  public final long readLong() throws IOException {
    return (((long)readInt()) << 32) | (readInt() & 0xFFFFFFFFL);
  }

  public final long readVLong() throws IOException {
    byte b = readByte();
    long i = b & 0x7F;
    for (int shift = 7; (b & 0x80) != 0; shift += 7) {
      b = readByte();
      i |= (b & 0x7FL) << shift;
    }
    return i;
  }

  public final String readString() throws IOException {
    int length = readVInt();
    if (chars == null || length > chars.length)
      chars = new char[length];
    readChars(chars, 0, length);
    return new String(chars, 0, length);
  }

  public final void readChars(char[] buffer, int start, int length)
       throws IOException {
    final int end = start + length;
    for (int i = start; i < end; i++) {
      byte b = readByte();
      if ((b & 0x80) == 0)
	buffer[i] = (char)(b & 0x7F);
      else if ((b & 0xE0) != 0xE0) {
	buffer[i] = (char)(((b & 0x1F) << 6)
		 | (readByte() & 0x3F));
      } else 
	buffer[i] = (char)(((b & 0x0F) << 12)
		| ((readByte() & 0x3F) << 6)
	        |  (readByte() & 0x3F));
    }
  }


  protected final void refill() throws IOException {
    long start = bufferStart + bufferPosition;
    long end = start + BUFFER_SIZE;
    if (end > length)				  // don't read past EOF
      end = length;
    bufferLength = (int)(end - start);
    if (bufferLength == 0)
      throw new IOException("read past EOF");

    if (buffer == null)
      buffer = new byte[BUFFER_SIZE];		  // allocate buffer lazily
    readInternal(buffer, 0, bufferLength);

    bufferStart = start;
    bufferPosition = 0;
  }

  abstract protected void readInternal(byte[] b, int offset, int length)
       throws IOException;

  abstract public void close() throws IOException;

  /** RandomAccessFile-like methods @see java.io.RandomAccessFile */
  public final long getFilePointer() {
    return bufferStart + bufferPosition;
  }

  public final void seek(long pos) throws IOException {
    if (pos >= bufferStart && pos < (bufferStart + bufferLength))
      bufferPosition = (int)(pos - bufferStart);  // seek within buffer
    else {
      bufferStart = pos;
      bufferPosition = 0;
      bufferLength = 0;				  // trigger refill() on read()
      seekInternal(pos);
    }
  }
  abstract protected void seekInternal(long pos) throws IOException;

  public final long length() {
    return length;
  }

  public Object clone() {
    InputStream clone = null;
    try {
      clone = (InputStream)super.clone();
    } catch (CloneNotSupportedException e) {}

    if (buffer != null) {
      clone.buffer = new byte[BUFFER_SIZE];
      System.arraycopy(buffer, 0, clone.buffer, 0, bufferLength);
    }

    clone.chars = null;

    return clone;
  }

}