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Lucene example source code file (BufferedIndexInput.java)

This example Lucene source code file (BufferedIndexInput.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

buffer_size, bufferedindexinput, bufferedindexinput, eof, eof, illegalargumentexception, indexinput, io, ioexception, ioexception, object, override, override

The Lucene BufferedIndexInput.java source code

package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/** Base implementation class for buffered {@link IndexInput}. */
public abstract class BufferedIndexInput extends IndexInput {

  /** Default buffer size */
  public static final int BUFFER_SIZE = 1024;

  private int bufferSize = BUFFER_SIZE;
  
  protected byte[] buffer;
  
  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

  @Override
  public byte readByte() throws IOException {
    if (bufferPosition >= bufferLength)
      refill();
    return buffer[bufferPosition++];
  }

  public BufferedIndexInput() {}

  /** Inits BufferedIndexInput with a specific bufferSize */
  public BufferedIndexInput(int bufferSize) {
    checkBufferSize(bufferSize);
    this.bufferSize = bufferSize;
  }

  /** Change the buffer size used by this IndexInput */
  public void setBufferSize(int newSize) {
    assert buffer == null || bufferSize == buffer.length: "buffer=" + buffer + " bufferSize=" + bufferSize + " buffer.length=" + (buffer != null ? buffer.length : 0);
    if (newSize != bufferSize) {
      checkBufferSize(newSize);
      bufferSize = newSize;
      if (buffer != null) {
        // Resize the existing buffer and carefully save as
        // many bytes as possible starting from the current
        // bufferPosition
        byte[] newBuffer = new byte[newSize];
        final int leftInBuffer = bufferLength-bufferPosition;
        final int numToCopy;
        if (leftInBuffer > newSize)
          numToCopy = newSize;
        else
          numToCopy = leftInBuffer;
        System.arraycopy(buffer, bufferPosition, newBuffer, 0, numToCopy);
        bufferStart += bufferPosition;
        bufferPosition = 0;
        bufferLength = numToCopy;
        newBuffer(newBuffer);
      }
    }
  }

  protected void newBuffer(byte[] newBuffer) {
    // Subclasses can do something here
    buffer = newBuffer;
  }

  /** Returns buffer size.  @see #setBufferSize */
  public int getBufferSize() {
    return bufferSize;
  }

  private void checkBufferSize(int bufferSize) {
    if (bufferSize <= 0)
      throw new IllegalArgumentException("bufferSize must be greater than 0 (got " + bufferSize + ")");
  }

  @Override
  public void readBytes(byte[] b, int offset, int len) throws IOException {
    readBytes(b, offset, len, true);
  }

  @Override
  public void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException {

    if(len <= (bufferLength-bufferPosition)){
      // the buffer contains enough data to satisfy this request
      if(len>0) // to allow b to be null if len is 0...
        System.arraycopy(buffer, bufferPosition, b, offset, len);
      bufferPosition+=len;
    } else {
      // the buffer does not have enough data. First serve all we've got.
      int available = bufferLength - bufferPosition;
      if(available > 0){
        System.arraycopy(buffer, bufferPosition, b, offset, available);
        offset += available;
        len -= available;
        bufferPosition += available;
      }
      // and now, read the remaining 'len' bytes:
      if (useBuffer && len<bufferSize){
        // If the amount left to read is small enough, and
        // we are allowed to use our buffer, do it in the usual
        // buffered way: fill the buffer and copy from it:
        refill();
        if(bufferLength<len){
          // Throw an exception when refill() could not read len bytes:
          System.arraycopy(buffer, 0, b, offset, bufferLength);
          throw new IOException("read past EOF");
        } else {
          System.arraycopy(buffer, 0, b, offset, len);
          bufferPosition=len;
        }
      } else {
        // The amount left to read is larger than the buffer
        // or we've been asked to not use our buffer -
        // there's no performance reason not to read it all
        // at once. Note that unlike the previous code of
        // this function, there is no need to do a seek
        // here, because there's no need to reread what we
        // had in the buffer.
        long after = bufferStart+bufferPosition+len;
        if(after > length())
          throw new IOException("read past EOF");
        readInternal(b, offset, len);
        bufferStart = after;
        bufferPosition = 0;
        bufferLength = 0;                    // trigger refill() on read
      }
    }
  }
  
  @Override
  public int readInt() throws IOException {
    if (4 <= (bufferLength-bufferPosition)) {
      return ((buffer[bufferPosition++] & 0xFF) << 24) | ((buffer[bufferPosition++] & 0xFF) << 16)
        | ((buffer[bufferPosition++] & 0xFF) <<  8) |  (buffer[bufferPosition++] & 0xFF);
    } else {
      return super.readInt();
    }
  }
  
  @Override
  public long readLong() throws IOException {
    if (8 <= (bufferLength-bufferPosition)) {
      final int i1 = ((buffer[bufferPosition++] & 0xff) << 24) | ((buffer[bufferPosition++] & 0xff) << 16) |
        ((buffer[bufferPosition++] & 0xff) << 8) | (buffer[bufferPosition++] & 0xff);
      final int i2 = ((buffer[bufferPosition++] & 0xff) << 24) | ((buffer[bufferPosition++] & 0xff) << 16) |
        ((buffer[bufferPosition++] & 0xff) << 8) | (buffer[bufferPosition++] & 0xff);
      return (((long)i1) << 32) | (i2 & 0xFFFFFFFFL);
    } else {
      return super.readLong();
    }
  }

  @Override
  public int readVInt() throws IOException {
    if (5 <= (bufferLength-bufferPosition)) {
      byte b = buffer[bufferPosition++];
      int i = b & 0x7F;
      for (int shift = 7; (b & 0x80) != 0; shift += 7) {
        b = buffer[bufferPosition++];
        i |= (b & 0x7F) << shift;
      }
      return i;
    } else {
      return super.readVInt();
    }
  }
  
  @Override
  public long readVLong() throws IOException {
    if (9 <= bufferLength-bufferPosition) {
      byte b = buffer[bufferPosition++];
      long i = b & 0x7F;
      for (int shift = 7; (b & 0x80) != 0; shift += 7) {
        b = buffer[bufferPosition++];
        i |= (b & 0x7FL) << shift;
      }
      return i;
    } else {
      return super.readVLong();
    }
  }
  
  private void refill() throws IOException {
    long start = bufferStart + bufferPosition;
    long end = start + bufferSize;
    if (end > length())				  // don't read past EOF
      end = length();
    int newLength = (int)(end - start);
    if (newLength <= 0)
      throw new IOException("read past EOF");

    if (buffer == null) {
      newBuffer(new byte[bufferSize]);  // allocate buffer lazily
      seekInternal(bufferStart);
    }
    readInternal(buffer, 0, newLength);
    bufferLength = newLength;
    bufferStart = start;
    bufferPosition = 0;
  }

  /** Expert: implements buffer refill.  Reads bytes from the current position
   * in the input.
   * @param b the array to read bytes into
   * @param offset the offset in the array to start storing bytes
   * @param length the number of bytes to read
   */
  protected abstract void readInternal(byte[] b, int offset, int length)
          throws IOException;

  @Override
  public long getFilePointer() { return bufferStart + bufferPosition; }

  @Override
  public 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);
    }
  }

  /** Expert: implements seek.  Sets current position in this file, where the
   * next {@link #readInternal(byte[],int,int)} will occur.
   * @see #readInternal(byte[],int,int)
   */
  protected abstract void seekInternal(long pos) throws IOException;

  @Override
  public Object clone() {
    BufferedIndexInput clone = (BufferedIndexInput)super.clone();

    clone.buffer = null;
    clone.bufferLength = 0;
    clone.bufferPosition = 0;
    clone.bufferStart = getFilePointer();

    return clone;
  }

  /**
   * Flushes the in-memory bufer to the given output, copying at most
   * <code>numBytes.
   * <p>
   * <b>NOTE: this method does not refill the buffer, however it does
   * advance the buffer position.
   * 
   * @return the number of bytes actually flushed from the in-memory buffer.
   */
  protected int flushBuffer(IndexOutput out, long numBytes) throws IOException {
    int toCopy = bufferLength - bufferPosition;
    if (toCopy > numBytes) {
      toCopy = (int) numBytes;
    }
    if (toCopy > 0) {
      out.writeBytes(buffer, bufferPosition, toCopy);
      bufferPosition += toCopy;
    }
    return toCopy;
  }
  
  @Override
  public void copyBytes(IndexOutput out, long numBytes) throws IOException {
    assert numBytes >= 0: "numBytes=" + numBytes;

    while (numBytes > 0) {
      if (bufferLength == bufferPosition) {
        refill();
      }
      numBytes -= flushBuffer(out, numBytes);
    }
  }
  
}

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