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Lucene example source code file (ConstantScoreQuery.java)

This example Lucene source code file (ConstantScoreQuery.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

constantscorequery, constantscorequery, constantscorer, docidsetiterator, explanation, filter, io, ioexception, ioexception, override, override, query, scorer, scorer, util, weight

The Lucene ConstantScoreQuery.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.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.ToStringUtils;

import java.io.IOException;
import java.util.Set;

/**
 * A query that wraps another query or a filter and simply returns a constant score equal to the
 * query boost for every document that matches the filter or query.
 * For queries it therefore simply strips of all scores and returns a constant one.
 *
 * <p>NOTE: if the wrapped filter is an instance of
 * {@link CachingWrapperFilter}, you'll likely want to
 * enforce deletions in the filter (using either {@link
 * CachingWrapperFilter.DeletesMode#RECACHE} or {@link
 * CachingWrapperFilter.DeletesMode#DYNAMIC}).
 */
public class ConstantScoreQuery extends Query {
  protected final Filter filter;
  protected final Query query;

  /** Strips off scores from the passed in Query. The hits will get a constant score
   * dependent on the boost factor of this query. */
  public ConstantScoreQuery(Query query) {
    if (query == null)
      throw new NullPointerException("Query may not be null");
    this.filter = null;
    this.query = query;
  }

  /** Wraps a Filter as a Query. The hits will get a constant score
   * dependent on the boost factor of this query.
   * If you simply want to strip off scores from a Query, no longer use
   * {@code new ConstantScoreQuery(new QueryWrapperFilter(query))}, instead
   * use {@link #ConstantScoreQuery(Query)}!
   */
  public ConstantScoreQuery(Filter filter) {
    if (filter == null)
      throw new NullPointerException("Filter may not be null");
    this.filter = filter;
    this.query = null;
  }

  /** Returns the encapsulated filter, returns {@code null} if a query is wrapped. */
  public Filter getFilter() {
    return filter;
  }

  /** Returns the encapsulated query, returns {@code null} if a filter is wrapped. */
  public Query getQuery() {
    return query;
  }

  @Override
  public Query rewrite(IndexReader reader) throws IOException {
    if (query != null) {
      Query rewritten = query.rewrite(reader);
      if (rewritten != query) {
        rewritten = new ConstantScoreQuery(rewritten);
        rewritten.setBoost(this.getBoost());
        return rewritten;
      }
    }
    return this;
  }

  @Override
  public void extractTerms(Set<Term> terms) {
    // TODO: OK to not add any terms when wrapped a filter
    // and used with MultiSearcher, but may not be OK for
    // highlighting.
    // If a query was wrapped, we delegate to query.
    if (query != null)
      query.extractTerms(terms);
  }

  protected class ConstantWeight extends Weight {
    private final Weight innerWeight;
    private final Similarity similarity;
    private float queryNorm;
    private float queryWeight;
    
    public ConstantWeight(Searcher searcher) throws IOException {
      this.similarity = getSimilarity(searcher);
      this.innerWeight = (query == null) ? null : query.createWeight(searcher);
    }

    @Override
    public Query getQuery() {
      return ConstantScoreQuery.this;
    }

    @Override
    public float getValue() {
      return queryWeight;
    }

    @Override
    public float sumOfSquaredWeights() throws IOException {
      // we calculate sumOfSquaredWeights of the inner weight, but ignore it (just to initialize everything)
      if (innerWeight != null) innerWeight.sumOfSquaredWeights();
      queryWeight = getBoost();
      return queryWeight * queryWeight;
    }

    @Override
    public void normalize(float norm) {
      this.queryNorm = norm;
      queryWeight *= this.queryNorm;
      // we normalize the inner weight, but ignore it (just to initialize everything)
      if (innerWeight != null) innerWeight.normalize(norm);
    }

    @Override
    public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
      final DocIdSetIterator disi;
      if (filter != null) {
        assert query == null;
        final DocIdSet dis = filter.getDocIdSet(reader);
        if (dis == null)
          return null;
        disi = dis.iterator();
      } else {
        assert query != null && innerWeight != null;
        disi =
          innerWeight.scorer(reader, scoreDocsInOrder, topScorer);
      }
      if (disi == null)
        return null;
      return new ConstantScorer(similarity, disi, this);
    }
    
    @Override
    public boolean scoresDocsOutOfOrder() {
      return (innerWeight != null) ? innerWeight.scoresDocsOutOfOrder() : false;
    }

    @Override
    public Explanation explain(IndexReader reader, int doc) throws IOException {
      final Scorer cs = scorer(reader, true, false);
      final boolean exists = (cs != null && cs.advance(doc) == doc);

      final ComplexExplanation result = new ComplexExplanation();
      if (exists) {
        result.setDescription(ConstantScoreQuery.this.toString() + ", product of:");
        result.setValue(queryWeight);
        result.setMatch(Boolean.TRUE);
        result.addDetail(new Explanation(getBoost(), "boost"));
        result.addDetail(new Explanation(queryNorm, "queryNorm"));
      } else {
        result.setDescription(ConstantScoreQuery.this.toString() + " doesn't match id " + doc);
        result.setValue(0);
        result.setMatch(Boolean.FALSE);
      }
      return result;
    }
  }

  protected class ConstantScorer extends Scorer {
    final DocIdSetIterator docIdSetIterator;
    final float theScore;

    public ConstantScorer(Similarity similarity, DocIdSetIterator docIdSetIterator, Weight w) throws IOException {
      super(similarity,w);
      theScore = w.getValue();
      this.docIdSetIterator = docIdSetIterator;
    }

    @Override
    public int nextDoc() throws IOException {
      return docIdSetIterator.nextDoc();
    }
    
    @Override
    public int docID() {
      return docIdSetIterator.docID();
    }

    @Override
    public float score() throws IOException {
      return theScore;
    }

    @Override
    public int advance(int target) throws IOException {
      return docIdSetIterator.advance(target);
    }
    
    private Collector wrapCollector(final Collector collector) {
      return new Collector() {
        @Override
        public void setScorer(Scorer scorer) throws IOException {
          // we must wrap again here, but using the scorer passed in as parameter:
          collector.setScorer(new ConstantScorer(ConstantScorer.this.getSimilarity(),
            scorer, ConstantScorer.this.weight));
        }
        
        @Override
        public void collect(int doc) throws IOException {
          collector.collect(doc);
        }
        
        @Override
        public void setNextReader(IndexReader reader, int docBase) throws IOException {
          collector.setNextReader(reader, docBase);
        }
        
        @Override
        public boolean acceptsDocsOutOfOrder() {
          return collector.acceptsDocsOutOfOrder();
        }
      };
    }

    // this optimization allows out of order scoring as top scorer!
    @Override
    public void score(Collector collector) throws IOException {
      if (docIdSetIterator instanceof Scorer) {
        ((Scorer) docIdSetIterator).score(wrapCollector(collector));
      } else {
        super.score(collector);
      }
    }

    // this optimization allows out of order scoring as top scorer,
    // TODO: theoretically this method should not be called because its protected and
    // this class does not use it, it should be public in Scorer!
    @Override
    protected boolean score(Collector collector, int max, int firstDocID) throws IOException {
      if (docIdSetIterator instanceof Scorer) {
        return ((Scorer) docIdSetIterator).score(wrapCollector(collector), max, firstDocID);
      } else {
        return super.score(collector, max, firstDocID);
      }
    }
  }

  @Override
  public Weight createWeight(Searcher searcher) throws IOException {
    return new ConstantScoreQuery.ConstantWeight(searcher);
  }

  @Override
  public String toString(String field) {
    return new StringBuilder("ConstantScore(")
      .append((query == null) ? filter.toString() : query.toString(field))
      .append(')')
      .append(ToStringUtils.boost(getBoost()))
      .toString();
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (!super.equals(o))
      return false;
    if (o instanceof ConstantScoreQuery) {
      final ConstantScoreQuery other = (ConstantScoreQuery) o;
      return 
        ((this.filter == null) ? other.filter == null : this.filter.equals(other.filter)) &&
        ((this.query == null) ? other.query == null : this.query.equals(other.query));
    }
    return false;
  }

  @Override
  public int hashCode() {
    return 31 * super.hashCode() +
      ((query == null) ? filter : query).hashCode();
  }

}

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