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Lucene example source code file (CustomScoreProvider.java)

This example Lucene source code file (CustomScoreProvider.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

customscoreprovider, customscoreprovider, explanation, explanation, indexreader, indexreader, io, ioexception, ioexception

The Lucene CustomScoreProvider.java source code

package org.apache.lucene.search.function;

/**
 * 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.search.Explanation;
import org.apache.lucene.search.FieldCache; // for javadocs

/**
 * An instance of this subclass should be returned by
 * {@link CustomScoreQuery#getCustomScoreProvider}, if you want
 * to modify the custom score calculation of a {@link CustomScoreQuery}.
 * <p>Since Lucene 2.9, queries operate on each segment of an index separately,
 * so the protected {@link #reader} field can be used to resolve doc IDs,
 * as the supplied <code>doc ID is per-segment and without knowledge
 * of the IndexReader you cannot access the document or {@link FieldCache}.
 * 
 * @lucene.experimental
 * @since 2.9.2
 */
public class CustomScoreProvider {

  protected final IndexReader reader;

  /**
   * Creates a new instance of the provider class for the given {@link IndexReader}.
   */
  public CustomScoreProvider(IndexReader reader) {
    this.reader = reader;
  }

  /**
   * Compute a custom score by the subQuery score and a number of 
   * {@link ValueSourceQuery} scores.
   * <p> 
   * Subclasses can override this method to modify the custom score.  
   * <p>
   * If your custom scoring is different than the default herein you 
   * should override at least one of the two customScore() methods.
   * If the number of ValueSourceQueries is always < 2 it is 
   * sufficient to override the other 
   * {@link #customScore(int, float, float) customScore()} 
   * method, which is simpler. 
   * <p>
   * The default computation herein is a multiplication of given scores:
   * <pre>
   *     ModifiedScore = valSrcScore * valSrcScores[0] * valSrcScores[1] * ...
   * </pre>
   * 
   * @param doc id of scored doc. 
   * @param subQueryScore score of that doc by the subQuery.
   * @param valSrcScores scores of that doc by the ValueSourceQuery.
   * @return custom score.
   */
  public float customScore(int doc, float subQueryScore, float valSrcScores[]) throws IOException {
    if (valSrcScores.length == 1) {
      return customScore(doc, subQueryScore, valSrcScores[0]);
    }
    if (valSrcScores.length == 0) {
      return customScore(doc, subQueryScore, 1);
    }
    float score = subQueryScore;
    for(int i = 0; i < valSrcScores.length; i++) {
      score *= valSrcScores[i];
    }
    return score;
  }

  /**
   * Compute a custom score by the subQuery score and the ValueSourceQuery score.
   * <p> 
   * Subclasses can override this method to modify the custom score.
   * <p>
   * If your custom scoring is different than the default herein you 
   * should override at least one of the two customScore() methods.
   * If the number of ValueSourceQueries is always < 2 it is 
   * sufficient to override this customScore() method, which is simpler. 
   * <p>
   * The default computation herein is a multiplication of the two scores:
   * <pre>
   *     ModifiedScore = subQueryScore * valSrcScore
   * </pre>
   *
   * @param doc id of scored doc. 
   * @param subQueryScore score of that doc by the subQuery.
   * @param valSrcScore score of that doc by the ValueSourceQuery.
   * @return custom score.
   */
  public float customScore(int doc, float subQueryScore, float valSrcScore) throws IOException {
    return subQueryScore * valSrcScore;
  }

  /**
   * Explain the custom score.
   * Whenever overriding {@link #customScore(int, float, float[])}, 
   * this method should also be overridden to provide the correct explanation
   * for the part of the custom scoring.
   *  
   * @param doc doc being explained.
   * @param subQueryExpl explanation for the sub-query part.
   * @param valSrcExpls explanation for the value source part.
   * @return an explanation for the custom score
   */
  public Explanation customExplain(int doc, Explanation subQueryExpl, Explanation valSrcExpls[]) throws IOException {
    if (valSrcExpls.length == 1) {
      return customExplain(doc, subQueryExpl, valSrcExpls[0]);
    }
    if (valSrcExpls.length == 0) {
      return subQueryExpl;
    }
    float valSrcScore = 1;
    for (int i = 0; i < valSrcExpls.length; i++) {
      valSrcScore *= valSrcExpls[i].getValue();
    }
    Explanation exp = new Explanation( valSrcScore * subQueryExpl.getValue(), "custom score: product of:");
    exp.addDetail(subQueryExpl);
    for (int i = 0; i < valSrcExpls.length; i++) {
      exp.addDetail(valSrcExpls[i]);
    }
    return exp;
  }
  
  /**
   * Explain the custom score.
   * Whenever overriding {@link #customScore(int, float, float)}, 
   * this method should also be overridden to provide the correct explanation
   * for the part of the custom scoring.
   *  
   * @param doc doc being explained.
   * @param subQueryExpl explanation for the sub-query part.
   * @param valSrcExpl explanation for the value source part.
   * @return an explanation for the custom score
   */
  public Explanation customExplain(int doc, Explanation subQueryExpl, Explanation valSrcExpl) throws IOException {
    float valSrcScore = 1;
    if (valSrcExpl != null) {
      valSrcScore *= valSrcExpl.getValue();
    }
    Explanation exp = new Explanation( valSrcScore * subQueryExpl.getValue(), "custom score: product of:");
    exp.addDetail(subQueryExpl);
    exp.addDetail(valSrcExpl);
    return exp;
  }

}

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