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Lucene example source code file (BooleanScorer.java)

This example Lucene source code file (BooleanScorer.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

booleanscorercollector, bucket, bucket, bucketscorer, buckettable, collector, io, ioexception, ioexception, no_more_docs, override, override, scorer, subscorer, subscorer, util

The Lucene BooleanScorer.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.List;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.BooleanClause.Occur;

/* Description from Doug Cutting (excerpted from
 * LUCENE-1483):
 *
 * BooleanScorer uses a ~16k array to score windows of
 * docs. So it scores docs 0-16k first, then docs 16-32k,
 * etc. For each window it iterates through all query terms
 * and accumulates a score in table[doc%16k]. It also stores
 * in the table a bitmask representing which terms
 * contributed to the score. Non-zero scores are chained in
 * a linked list. At the end of scoring each window it then
 * iterates through the linked list and, if the bitmask
 * matches the boolean constraints, collects a hit. For
 * boolean queries with lots of frequent terms this can be
 * much faster, since it does not need to update a priority
 * queue for each posting, instead performing constant-time
 * operations per posting. The only downside is that it
 * results in hits being delivered out-of-order within the
 * window, which means it cannot be nested within other
 * scorers. But it works well as a top-level scorer.
 *
 * The new BooleanScorer2 implementation instead works by
 * merging priority queues of postings, albeit with some
 * clever tricks. For example, a pure conjunction (all terms
 * required) does not require a priority queue. Instead it
 * sorts the posting streams at the start, then repeatedly
 * skips the first to to the last. If the first ever equals
 * the last, then there's a hit. When some terms are
 * required and some terms are optional, the conjunction can
 * be evaluated first, then the optional terms can all skip
 * to the match and be added to the score. Thus the
 * conjunction can reduce the number of priority queue
 * updates for the optional terms. */

final class BooleanScorer extends Scorer {
  
  private static final class BooleanScorerCollector extends Collector {
    private BucketTable bucketTable;
    private int mask;
    private Scorer scorer;
    
    public BooleanScorerCollector(int mask, BucketTable bucketTable) {
      this.mask = mask;
      this.bucketTable = bucketTable;
    }
    
    @Override
    public void collect(final int doc) throws IOException {
      final BucketTable table = bucketTable;
      final int i = doc & BucketTable.MASK;
      Bucket bucket = table.buckets[i];
      if (bucket == null)
        table.buckets[i] = bucket = new Bucket();
      
      if (bucket.doc != doc) {                    // invalid bucket
        bucket.doc = doc;                         // set doc
        bucket.score = scorer.score();            // initialize score
        bucket.bits = mask;                       // initialize mask
        bucket.coord = 1;                         // initialize coord

        bucket.next = table.first;                // push onto valid list
        table.first = bucket;
      } else {                                    // valid bucket
        bucket.score += scorer.score();           // increment score
        bucket.bits |= mask;                      // add bits in mask
        bucket.coord++;                           // increment coord
      }
    }
    
    @Override
    public void setNextReader(IndexReader reader, int docBase) {
      // not needed by this implementation
    }
    
    @Override
    public void setScorer(Scorer scorer) throws IOException {
      this.scorer = scorer;
    }
    
    @Override
    public boolean acceptsDocsOutOfOrder() {
      return true;
    }

  }
  
  // An internal class which is used in score(Collector, int) for setting the
  // current score. This is required since Collector exposes a setScorer method
  // and implementations that need the score will call scorer.score().
  // Therefore the only methods that are implemented are score() and doc().
  private static final class BucketScorer extends Scorer {

    float score;
    int doc = NO_MORE_DOCS;
    int freq;
    
    public BucketScorer(Weight weight) { super(weight); }
    
    @Override
    public int advance(int target) throws IOException { return NO_MORE_DOCS; }

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

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

    @Override
    public int nextDoc() throws IOException { return NO_MORE_DOCS; }
    
    @Override
    public float score() throws IOException { return score; }
    
  }

  static final class Bucket {
    int doc = -1;            // tells if bucket is valid
    float score;             // incremental score
    int bits;                // used for bool constraints
    int coord;               // count of terms in score
    Bucket next;             // next valid bucket
  }
  
  /** A simple hash table of document scores within a range. */
  static final class BucketTable {
    public static final int SIZE = 1 << 11;
    public static final int MASK = SIZE - 1;

    final Bucket[] buckets = new Bucket[SIZE];
    Bucket first = null;                          // head of valid list
  
    public BucketTable() {}

    public Collector newCollector(int mask) {
      return new BooleanScorerCollector(mask, this);
    }

    public int size() { return SIZE; }
  }

  static final class SubScorer {
    public Scorer scorer;
    // TODO: re-enable this if BQ ever sends us required clauses
    //public boolean required = false;
    public boolean prohibited = false;
    public Collector collector;
    public SubScorer next;

    public SubScorer(Scorer scorer, boolean required, boolean prohibited,
        Collector collector, SubScorer next)
      throws IOException {
      if (required) {
        throw new IllegalArgumentException("this scorer cannot handle required=true");
      }
      this.scorer = scorer;
      // TODO: re-enable this if BQ ever sends us required clauses
      //this.required = required;
      this.prohibited = prohibited;
      this.collector = collector;
      this.next = next;
    }
  }
  
  private SubScorer scorers = null;
  private BucketTable bucketTable = new BucketTable();
  private final float[] coordFactors;
  // TODO: re-enable this if BQ ever sends us required clauses
  //private int requiredMask = 0;
  private int prohibitedMask = 0;
  private int nextMask = 1;
  private final int minNrShouldMatch;
  private int end;
  private Bucket current;
  private int doc = -1;
  
  BooleanScorer(Weight weight, boolean disableCoord, Similarity similarity, int minNrShouldMatch,
      List<Scorer> optionalScorers, List prohibitedScorers, int maxCoord) throws IOException {
    super(weight);
    this.minNrShouldMatch = minNrShouldMatch;

    if (optionalScorers != null && optionalScorers.size() > 0) {
      for (Scorer scorer : optionalScorers) {
        if (scorer.nextDoc() != NO_MORE_DOCS) {
          scorers = new SubScorer(scorer, false, false, bucketTable.newCollector(0), scorers);
        }
      }
    }
    
    if (prohibitedScorers != null && prohibitedScorers.size() > 0) {
      for (Scorer scorer : prohibitedScorers) {
        int mask = nextMask;
        nextMask = nextMask << 1;
        prohibitedMask |= mask;                     // update prohibited mask
        if (scorer.nextDoc() != NO_MORE_DOCS) {
          scorers = new SubScorer(scorer, false, true, bucketTable.newCollector(mask), scorers);
        }
      }
    }

    coordFactors = new float[optionalScorers.size() + 1];
    for (int i = 0; i < coordFactors.length; i++) {
      coordFactors[i] = disableCoord ? 1.0f : similarity.coord(i, maxCoord); 
    }
  }

  // firstDocID is ignored since nextDoc() initializes 'current'
  @Override
  protected boolean score(Collector collector, int max, int firstDocID) throws IOException {
    boolean more;
    Bucket tmp;
    BucketScorer bs = new BucketScorer(weight);
    // The internal loop will set the score and doc before calling collect.
    collector.setScorer(bs);
    do {
      bucketTable.first = null;
      
      while (current != null) {         // more queued 

        // check prohibited & required
        if ((current.bits & prohibitedMask) == 0) {

            // TODO: re-enable this if BQ ever sends us required
            // clauses
            //&& (current.bits & requiredMask) == requiredMask) {
          
          if (current.doc >= max){
            tmp = current;
            current = current.next;
            tmp.next = bucketTable.first;
            bucketTable.first = tmp;
            continue;
          }
          
          if (current.coord >= minNrShouldMatch) {
            bs.score = current.score * coordFactors[current.coord];
            bs.doc = current.doc;
            bs.freq = current.coord;
            collector.collect(current.doc);
          }
        }
        
        current = current.next;         // pop the queue
      }
      
      if (bucketTable.first != null){
        current = bucketTable.first;
        bucketTable.first = current.next;
        return true;
      }

      // refill the queue
      more = false;
      end += BucketTable.SIZE;
      for (SubScorer sub = scorers; sub != null; sub = sub.next) {
        int subScorerDocID = sub.scorer.docID();
        if (subScorerDocID != NO_MORE_DOCS) {
          more |= sub.scorer.score(sub.collector, end, subScorerDocID);
        }
      }
      current = bucketTable.first;
      
    } while (current != null || more);

    return false;
  }
  
  @Override
  public int advance(int target) throws IOException {
    throw new UnsupportedOperationException();
  }

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

  @Override
  public int nextDoc() throws IOException {
    boolean more;
    do {
      while (bucketTable.first != null) {         // more queued
        current = bucketTable.first;
        bucketTable.first = current.next;         // pop the queue

        // check prohibited & required, and minNrShouldMatch
        if ((current.bits & prohibitedMask) == 0 &&
            current.coord >= minNrShouldMatch) {
          // TODO: re-enable this if BQ ever sends us required clauses
          // (current.bits & requiredMask) == requiredMask &&
          return doc = current.doc;
        }
      }

      // refill the queue
      more = false;
      end += BucketTable.SIZE;
      for (SubScorer sub = scorers; sub != null; sub = sub.next) {
        int subScorerDocID = sub.scorer.docID();
        if (subScorerDocID != NO_MORE_DOCS) {
          more |= sub.scorer.score(sub.collector, end, subScorerDocID);
        }
      }
    } while (bucketTable.first != null || more);

    return doc = NO_MORE_DOCS;
  }

  @Override
  public float score() {
    return current.score * coordFactors[current.coord];
  }

  @Override
  public void score(Collector collector) throws IOException {
    score(collector, Integer.MAX_VALUE, nextDoc());
  }
  
  @Override
  public String toString() {
    StringBuilder buffer = new StringBuilder();
    buffer.append("boolean(");
    for (SubScorer sub = scorers; sub != null; sub = sub.next) {
      buffer.append(sub.scorer.toString());
      buffer.append(" ");
    }
    buffer.append(")");
    return buffer.toString();
  }
  
  @Override
  protected void visitSubScorers(Query parent, Occur relationship, ScorerVisitor<Query, Query, Scorer> visitor) {
    super.visitSubScorers(parent, relationship, visitor);
    final Query q = weight.getQuery();
    SubScorer sub = scorers;
    while(sub != null) {
      // TODO: re-enable this if BQ ever sends us required
      //clauses
      //if (sub.required) {
      //relationship = Occur.MUST;
      if (!sub.prohibited) {
        relationship = Occur.SHOULD;
      } else {
        // TODO: maybe it's pointless to do this, but, it is
        // possible the doc may still be collected, eg foo
        // OR (bar -fee)
        relationship = Occur.MUST_NOT;
      }
      sub.scorer.visitSubScorers(q, relationship, visitor);
      sub = sub.next;
    }
  }

}

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