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Lucene example source code file (ScoringRewrite.java)

This example Lucene source code file (ScoringRewrite.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

booleanquery, booleanquery, constant_score_boolean_query_rewrite, io, ioexception, ioexception, object, override, override, query, query, rewritemethod, scoring_boolean_query_rewrite, scoringrewrite, termquery

The Lucene ScoringRewrite.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 org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.MultiTermQuery.RewriteMethod;

/** @lucene.internal Only public to be accessible by spans package. */
public abstract class ScoringRewrite<Q extends Query> extends TermCollectingRewrite {

  /** A rewrite method that first translates each term into
   *  {@link BooleanClause.Occur#SHOULD} clause in a
   *  BooleanQuery, and keeps the scores as computed by the
   *  query.  Note that typically such scores are
   *  meaningless to the user, and require non-trivial CPU
   *  to compute, so it's almost always better to use {@link
   *  MultiTermQuery#CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} instead.
   *
   *  <p>NOTE: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static ScoringRewrite<BooleanQuery> SCORING_BOOLEAN_QUERY_REWRITE = new ScoringRewrite() {
    @Override
    protected BooleanQuery getTopLevelQuery() {
      return new BooleanQuery(true);
    }
    
    @Override
    protected void addClause(BooleanQuery topLevel, Term term, float boost) {
      final TermQuery tq = new TermQuery(term);
      tq.setBoost(boost);
      topLevel.add(tq, BooleanClause.Occur.SHOULD);
    }
    
    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return SCORING_BOOLEAN_QUERY_REWRITE;
    }    
  };
  
  /** Like {@link #SCORING_BOOLEAN_QUERY_REWRITE} except
   *  scores are not computed.  Instead, each matching
   *  document receives a constant score equal to the
   *  query's boost.
   * 
   *  <p>NOTE: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE = new RewriteMethod() {
    @Override
    public Query rewrite(IndexReader reader, MultiTermQuery query) throws IOException {
      final BooleanQuery bq = SCORING_BOOLEAN_QUERY_REWRITE.rewrite(reader, query);
      // TODO: if empty boolean query return NullQuery?
      if (bq.clauses().isEmpty())
        return bq;
      // strip the scores off
      final Query result = new ConstantScoreQuery(bq);
      result.setBoost(query.getBoost());
      return result;
    }

    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE;
    }
  };

  @Override
  public Q rewrite(final IndexReader reader, final MultiTermQuery query) throws IOException {
    final Q result = getTopLevelQuery();
    final int[] size = new int[1]; // "trick" to be able to make it final
    collectTerms(reader, query, new TermCollector() {
      public boolean collect(Term t, float boost) throws IOException {
        addClause(result, t, query.getBoost() * boost);
        size[0]++;
        return true;
      }
    });
    query.incTotalNumberOfTerms(size[0]);
    return result;
  }
}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene ScoringRewrite.java source code file:



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