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Lucene example source code file (ExactPhraseScorer.java)

This example Lucene source code file (ExactPhraseScorer.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

chunk, chunk, chunkstate, chunkstate, exactphrasescorer, io, ioexception, ioexception, override, override, score_cache_size, scorer, similarity, string, termpositions, util

The Lucene ExactPhraseScorer.java source code

package org.apache.lucene.search;

/**
 * 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.index.*;

final class ExactPhraseScorer extends Scorer {
  private final byte[] norms;
  private final float value;

  private static final int SCORE_CACHE_SIZE = 32;
  private final float[] scoreCache = new float[SCORE_CACHE_SIZE];

  private final int endMinus1;

  private final static int CHUNK = 4096;

  private int gen;
  private final int[] counts = new int[CHUNK];
  private final int[] gens = new int[CHUNK];

  boolean noDocs;

  private final static class ChunkState {
    final TermPositions posEnum;
    final int offset;
    final boolean useAdvance;
    int posUpto;
    int posLimit;
    int pos;
    int lastPos;

    public ChunkState(TermPositions posEnum, int offset, boolean useAdvance) {
      this.posEnum = posEnum;
      this.offset = offset;
      this.useAdvance = useAdvance;
    }
  }

  private final ChunkState[] chunkStates;

  private int docID = -1;
  private int freq;

  ExactPhraseScorer(Weight weight, PhraseQuery.PostingsAndFreq[] postings,
                    Similarity similarity, byte[] norms) throws IOException {
    super(similarity, weight);
    this.norms = norms;
    this.value = weight.getValue();

    chunkStates = new ChunkState[postings.length];

    endMinus1 = postings.length-1;

    for(int i=0;i<postings.length;i++) {

      // Coarse optimization: advance(target) is fairly
      // costly, so, if the relative freq of the 2nd
      // rarest term is not that much (> 1/5th) rarer than
      // the first term, then we just use .nextDoc() when
      // ANDing.  This buys ~15% gain for phrases where
      // freq of rarest 2 terms is close:
      final boolean useAdvance = postings[i].docFreq > 5*postings[0].docFreq;
      chunkStates[i] = new ChunkState(postings[i].postings, -postings[i].position, useAdvance);
      if (i > 0 && !postings[i].postings.next()) {
        noDocs = true;
        return;
      }
    }

    for (int i = 0; i < SCORE_CACHE_SIZE; i++) {
      scoreCache[i] = getSimilarity().tf((float) i) * value;
    }
  }

  @Override
  public int nextDoc() throws IOException {
    while(true) {

      // first (rarest) term
      if (!chunkStates[0].posEnum.next()) {
        docID = DocIdSetIterator.NO_MORE_DOCS;
        return docID;
      }
      
      final int doc = chunkStates[0].posEnum.doc();

      // not-first terms
      int i = 1;
      while(i < chunkStates.length) {
        final ChunkState cs = chunkStates[i];
        int doc2 = cs.posEnum.doc();
        if (cs.useAdvance) {
          if (doc2 < doc) {
            if (!cs.posEnum.skipTo(doc)) {
              docID = DocIdSetIterator.NO_MORE_DOCS;
              return docID;
            } else {
              doc2 = cs.posEnum.doc();
            }
          }
        } else {
          int iter = 0;
          while(doc2 < doc) {
            // safety net -- fallback to .skipTo if we've
            // done too many .nextDocs
            if (++iter == 50) {
              if (!cs.posEnum.skipTo(doc)) {
                docID = DocIdSetIterator.NO_MORE_DOCS;
                return docID;
              } else {
                doc2 = cs.posEnum.doc();
              }
              break;
            } else {
              if (cs.posEnum.next()) {
                doc2 = cs.posEnum.doc();
              } else {
                docID = DocIdSetIterator.NO_MORE_DOCS;
                return docID;
              }
            }
          }
        }
        if (doc2 > doc) {
          break;
        }
        i++;
      }

      if (i == chunkStates.length) {
        // this doc has all the terms -- now test whether
        // phrase occurs
        docID = doc;

        freq = phraseFreq();
        if (freq != 0) {
          return docID;
        }
      }
    }
  }

  @Override
  public int advance(int target) throws IOException {

    // first term
    if (!chunkStates[0].posEnum.skipTo(target)) {
      docID = DocIdSetIterator.NO_MORE_DOCS;
      return docID;
    }
    int doc = chunkStates[0].posEnum.doc();

    while(true) {
      
      // not-first terms
      int i = 1;
      while(i < chunkStates.length) {
        int doc2 = chunkStates[i].posEnum.doc();
        if (doc2 < doc) {
          if (!chunkStates[i].posEnum.skipTo(doc)) {
            docID = DocIdSetIterator.NO_MORE_DOCS;
            return docID;
          } else {
            doc2 = chunkStates[i].posEnum.doc();
          }
        }
        if (doc2 > doc) {
          break;
        }
        i++;
      }

      if (i == chunkStates.length) {
        // this doc has all the terms -- now test whether
        // phrase occurs
        docID = doc;
        freq = phraseFreq();
        if (freq != 0) {
          return docID;
        }
      }

      if (!chunkStates[0].posEnum.next()) {
        docID = DocIdSetIterator.NO_MORE_DOCS;
        return docID;
      } else {
        doc = chunkStates[0].posEnum.doc();
      }
    }
  }

  @Override
  public String toString() {
    return "ExactPhraseScorer(" + weight + ")";
  }

  @Override
  public float freq() {
    return freq;
  }

  @Override
  public int docID() {
    return docID;
  }

  @Override
  public float score() throws IOException {
    final float raw; // raw score
    if (freq < SCORE_CACHE_SIZE) {
      raw = scoreCache[freq];
    } else {
      raw = getSimilarity().tf((float) freq) * value;
    }
    return norms == null ? raw : raw * getSimilarity().decodeNormValue(norms[docID]); // normalize
  }

  private int phraseFreq() throws IOException {

    freq = 0;

    // init chunks
    for(int i=0;i<chunkStates.length;i++) {
      final ChunkState cs = chunkStates[i];
      cs.posLimit = cs.posEnum.freq();
      cs.pos = cs.offset + cs.posEnum.nextPosition();
      cs.posUpto = 1;
      cs.lastPos = -1;
    }

    int chunkStart = 0;
    int chunkEnd = CHUNK;

    // process chunk by chunk
    boolean end = false;

    // TODO: we could fold in chunkStart into offset and
    // save one subtract per pos incr

    while(!end) {

      gen++;

      if (gen == 0) {
        // wraparound
        Arrays.fill(gens, 0);
        gen++;
      }

      // first term
      {
        final ChunkState cs = chunkStates[0];
        while(cs.pos < chunkEnd) {
          if (cs.pos > cs.lastPos) {
            cs.lastPos = cs.pos;
            final int posIndex = cs.pos - chunkStart;
            counts[posIndex] = 1;
            assert gens[posIndex] != gen;
            gens[posIndex] = gen;
          }

          if (cs.posUpto == cs.posLimit) {
            end = true;
            break;
          }
          cs.posUpto++;
          cs.pos = cs.offset + cs.posEnum.nextPosition();
        }
      }

      // middle terms
      boolean any = true;
      for(int t=1;t<endMinus1;t++) {
        final ChunkState cs = chunkStates[t];
        any = false;
        while(cs.pos < chunkEnd) {
          if (cs.pos > cs.lastPos) {
            cs.lastPos = cs.pos;
            final int posIndex = cs.pos - chunkStart;
            if (posIndex >= 0 && gens[posIndex] == gen && counts[posIndex] == t) {
              // viable
              counts[posIndex]++;
              any = true;
            }
          }

          if (cs.posUpto == cs.posLimit) {
            end = true;
            break;
          }
          cs.posUpto++;
          cs.pos = cs.offset + cs.posEnum.nextPosition();
        }

        if (!any) {
          break;
        }
      }

      if (!any) {
        // petered out for this chunk
        chunkStart += CHUNK;
        chunkEnd += CHUNK;
        continue;
      }

      // last term

      {
        final ChunkState cs = chunkStates[endMinus1];
        while(cs.pos < chunkEnd) {
          if (cs.pos > cs.lastPos) {
            cs.lastPos = cs.pos;
            final int posIndex = cs.pos - chunkStart;
            if (posIndex >= 0 && gens[posIndex] == gen && counts[posIndex] == endMinus1) {
              freq++;
            }
          }

          if (cs.posUpto == cs.posLimit) {
            end = true;
            break;
          }
          cs.posUpto++;
          cs.pos = cs.offset + cs.posEnum.nextPosition();
        }
      }

      chunkStart += CHUNK;
      chunkEnd += CHUNK;
    }

    return freq;
  }
}

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