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Lucene example source code file (DefaultSkipListWriter.java)

This example Lucene source code file (DefaultSkipListWriter.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

defaultskiplistwriter, defaultskiplistwriter, indexoutput, indexoutput, io, ioexception, multilevelskiplistwriter, multilevelskiplistwriter, override, override, util

The Lucene DefaultSkipListWriter.java source code

package org.apache.lucene.index;

/**
 * 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;
import java.util.Arrays;

import org.apache.lucene.store.IndexOutput;


/**
 * Implements the skip list writer for the default posting list format
 * that stores positions and payloads.
 *
 */
class DefaultSkipListWriter extends MultiLevelSkipListWriter {
  private int[] lastSkipDoc;
  private int[] lastSkipPayloadLength;
  private long[] lastSkipFreqPointer;
  private long[] lastSkipProxPointer;
  
  private IndexOutput freqOutput;
  private IndexOutput proxOutput;

  private int curDoc;
  private boolean curStorePayloads;
  private int curPayloadLength;
  private long curFreqPointer;
  private long curProxPointer;
  
  DefaultSkipListWriter(int skipInterval, int numberOfSkipLevels, int docCount, IndexOutput freqOutput, IndexOutput proxOutput) {
    super(skipInterval, numberOfSkipLevels, docCount);
    this.freqOutput = freqOutput;
    this.proxOutput = proxOutput;
    
    lastSkipDoc = new int[numberOfSkipLevels];
    lastSkipPayloadLength = new int[numberOfSkipLevels];
    lastSkipFreqPointer = new long[numberOfSkipLevels];
    lastSkipProxPointer = new long[numberOfSkipLevels];
  }

  void setFreqOutput(IndexOutput freqOutput) {
    this.freqOutput = freqOutput;
  }

  void setProxOutput(IndexOutput proxOutput) {
    this.proxOutput = proxOutput;
  }

  /**
   * Sets the values for the current skip data. 
   */
  void setSkipData(int doc, boolean storePayloads, int payloadLength) {
    this.curDoc = doc;
    this.curStorePayloads = storePayloads;
    this.curPayloadLength = payloadLength;
    this.curFreqPointer = freqOutput.getFilePointer();
    if (proxOutput != null)
      this.curProxPointer = proxOutput.getFilePointer();
  }
  
  @Override
  protected void resetSkip() {
    super.resetSkip();
    Arrays.fill(lastSkipDoc, 0);
    Arrays.fill(lastSkipPayloadLength, -1);  // we don't have to write the first length in the skip list
    Arrays.fill(lastSkipFreqPointer, freqOutput.getFilePointer());
    if (proxOutput != null)
      Arrays.fill(lastSkipProxPointer, proxOutput.getFilePointer());
  }
  
  @Override
  protected void writeSkipData(int level, IndexOutput skipBuffer) throws IOException {
    // To efficiently store payloads in the posting lists we do not store the length of
    // every payload. Instead we omit the length for a payload if the previous payload had
    // the same length.
    // However, in order to support skipping the payload length at every skip point must be known.
    // So we use the same length encoding that we use for the posting lists for the skip data as well:
    // Case 1: current field does not store payloads
    //           SkipDatum                 --> DocSkip, FreqSkip, ProxSkip
    //           DocSkip,FreqSkip,ProxSkip --> VInt
    //           DocSkip records the document number before every SkipInterval th  document in TermFreqs. 
    //           Document numbers are represented as differences from the previous value in the sequence.
    // Case 2: current field stores payloads
    //           SkipDatum                 --> DocSkip, PayloadLength?, FreqSkip,ProxSkip
    //           DocSkip,FreqSkip,ProxSkip --> VInt
    //           PayloadLength             --> VInt    
    //         In this case DocSkip/2 is the difference between
    //         the current and the previous value. If DocSkip
    //         is odd, then a PayloadLength encoded as VInt follows,
    //         if DocSkip is even, then it is assumed that the
    //         current payload length equals the length at the previous
    //         skip point
    if (curStorePayloads) {
      int delta = curDoc - lastSkipDoc[level];
      if (curPayloadLength == lastSkipPayloadLength[level]) {
        // the current payload length equals the length at the previous skip point,
        // so we don't store the length again
        skipBuffer.writeVInt(delta * 2);
      } else {
        // the payload length is different from the previous one. We shift the DocSkip, 
        // set the lowest bit and store the current payload length as VInt.
        skipBuffer.writeVInt(delta * 2 + 1);
        skipBuffer.writeVInt(curPayloadLength);
        lastSkipPayloadLength[level] = curPayloadLength;
      }
    } else {
      // current field does not store payloads
      skipBuffer.writeVInt(curDoc - lastSkipDoc[level]);
    }
    skipBuffer.writeVInt((int) (curFreqPointer - lastSkipFreqPointer[level]));
    skipBuffer.writeVInt((int) (curProxPointer - lastSkipProxPointer[level]));

    lastSkipDoc[level] = curDoc;
    //System.out.println("write doc at level " + level + ": " + curDoc);
    
    lastSkipFreqPointer[level] = curFreqPointer;
    lastSkipProxPointer[level] = curProxPointer;
  }

}

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