Lucene example source code file (ConjunctionScorer.java)

This example Lucene source code file (ConjunctionScorer.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

collection, comparator, conjunctionscorer, io, ioexception, ioexception, no_more_docs, no_more_docs, override, override, scorer, scorer, util

The Lucene ConjunctionScorer.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 org.apache.lucene.util.ArrayUtil;
import java.io.IOException;
import java.util.Collection;
import java.util.Comparator;

/** Scorer for conjunctions, sets of queries, all of which are required. */
class ConjunctionScorer extends Scorer {
  
  private final Scorer[] scorers;
  private final float coord;
  private int lastDoc = -1;

  public ConjunctionScorer(Weight weight, float coord, Collection<Scorer> scorers) throws IOException {
    this(weight, coord, scorers.toArray(new Scorer[scorers.size()]));
  }

  public ConjunctionScorer(Weight weight, float coord, Scorer... scorers) throws IOException {
    super(weight);
    this.scorers = scorers;
    this.coord = coord;
    
    for (int i = 0; i < scorers.length; i++) {
      if (scorers[i].nextDoc() == NO_MORE_DOCS) {
        // If even one of the sub-scorers does not have any documents, this
        // scorer should not attempt to do any more work.
        lastDoc = NO_MORE_DOCS;
        return;
      }
    }

    // Sort the array the first time...
    // We don't need to sort the array in any future calls because we know
    // it will already start off sorted (all scorers on same doc).
    
    // Note that this comparator is not consistent with equals!
    // Also we use mergeSort here to be stable (so order of Scoreres that
    // match on first document keeps preserved):
    ArrayUtil.mergeSort(scorers, new Comparator<Scorer>() { // sort the array
      public int compare(Scorer o1, Scorer o2) {
        return o1.docID() - o2.docID();
      }
    });

    // NOTE: doNext() must be called before the re-sorting of the array later on.
    // The reason is this: assume there are 5 scorers, whose first docs are 1,
    // 2, 3, 5, 5 respectively. Sorting (above) leaves the array as is. Calling
    // doNext() here advances all the first scorers to 5 (or a larger doc ID
    // they all agree on). 
    // However, if we re-sort before doNext() is called, the order will be 5, 3,
    // 2, 1, 5 and then doNext() will stop immediately, since the first scorer's
    // docs equals the last one. So the invariant that after calling doNext() 
    // all scorers are on the same doc ID is broken.
    if (doNext() == NO_MORE_DOCS) {
      // The scorers did not agree on any document.
      lastDoc = NO_MORE_DOCS;
      return;
    }

    // If first-time skip distance is any predictor of
    // scorer sparseness, then we should always try to skip first on
    // those scorers.
    // Keep last scorer in it's last place (it will be the first
    // to be skipped on), but reverse all of the others so that
    // they will be skipped on in order of original high skip.
    int end = scorers.length - 1;
    int max = end >> 1;
    for (int i = 0; i < max; i++) {
      Scorer tmp = scorers[i];
      int idx = end - i - 1;
      scorers[i] = scorers[idx];
      scorers[idx] = tmp;
    }
  }

  private int doNext() throws IOException {
    int first = 0;
    int doc = scorers[scorers.length - 1].docID();
    Scorer firstScorer;
    while ((firstScorer = scorers[first]).docID() < doc) {
      doc = firstScorer.advance(doc);
      first = first == scorers.length - 1 ? 0 : first + 1;
    }
    return doc;
  }
  
  @Override
  public int advance(int target) throws IOException {
    if (lastDoc == NO_MORE_DOCS) {
      return lastDoc;
    } else if (scorers[(scorers.length - 1)].docID() < target) {
      scorers[(scorers.length - 1)].advance(target);
    }
    return lastDoc = doNext();
  }

  @Override
  public int docID() {
    return lastDoc;
  }
  
  @Override
  public int nextDoc() throws IOException {
    if (lastDoc == NO_MORE_DOCS) {
      return lastDoc;
    } else if (lastDoc == -1) {
      return lastDoc = scorers[scorers.length - 1].docID();
    }
    scorers[(scorers.length - 1)].nextDoc();
    return lastDoc = doNext();
  }
  
  @Override
  public float score() throws IOException {
    float sum = 0.0f;
    for (int i = 0; i < scorers.length; i++) {
      sum += scorers[i].score();
    }
    return sum * coord;
  }
}