bufferedindexinput.java

中文分词,中科院分词的改装版。使用java调用dll来实现的。

package org.apache.lucene.store;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 {
  static final int BUFFER_SIZE = BufferedIndexOutput.BUFFER_SIZE;

  private 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

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

  public 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
    }
  }

  private 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;
  }

  /** 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;

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

  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;

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

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

    return clone;
  }

}