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Lucene example source code file (QueryTermScorer.java)

This example Lucene source code file (QueryTermScorer.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

chartermattribute, hashmap, hashset, hashset, indexreader, querytermscorer, querytermscorer, scorer, string, string, textfragment, tokenstream, util, weightedterm, weightedterm

The Lucene QueryTermScorer.java source code

package org.apache.lucene.search.highlight;

/**
 * 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.util.HashMap;
import java.util.HashSet;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.Query;

/**
 * {@link Scorer} implementation which scores text fragments by the number of
 * unique query terms found. This class uses the {@link QueryTermExtractor}
 * class to process determine the query terms and their boosts to be used.
 */
// TODO: provide option to boost score of fragments near beginning of document
// based on fragment.getFragNum()
public class QueryTermScorer implements Scorer {
  
  TextFragment currentTextFragment = null;
  HashSet<String> uniqueTermsInFragment;

  float totalScore = 0;
  float maxTermWeight = 0;
  private HashMap<String,WeightedTerm> termsToFind;

  private CharTermAttribute termAtt;

  /**
   * 
   * @param query a Lucene query (ideally rewritten using query.rewrite before
   *        being passed to this class and the searcher)
   */
  public QueryTermScorer(Query query) {
    this(QueryTermExtractor.getTerms(query));
  }

  /**
   * 
   * @param query a Lucene query (ideally rewritten using query.rewrite before
   *        being passed to this class and the searcher)
   * @param fieldName the Field name which is used to match Query terms
   */
  public QueryTermScorer(Query query, String fieldName) {
    this(QueryTermExtractor.getTerms(query, false, fieldName));
  }

  /**
   * 
   * @param query a Lucene query (ideally rewritten using query.rewrite before
   *        being passed to this class and the searcher)
   * @param reader used to compute IDF which can be used to a) score selected
   *        fragments better b) use graded highlights eg set font color
   *        intensity
   * @param fieldName the field on which Inverse Document Frequency (IDF)
   *        calculations are based
   */
  public QueryTermScorer(Query query, IndexReader reader, String fieldName) {
    this(QueryTermExtractor.getIdfWeightedTerms(query, reader, fieldName));
  }

  public QueryTermScorer(WeightedTerm[] weightedTerms) {
    termsToFind = new HashMap<String,WeightedTerm>();
    for (int i = 0; i < weightedTerms.length; i++) {
      WeightedTerm existingTerm = termsToFind
          .get(weightedTerms[i].term);
      if ((existingTerm == null)
          || (existingTerm.weight < weightedTerms[i].weight)) {
        // if a term is defined more than once, always use the highest scoring
        // weight
        termsToFind.put(weightedTerms[i].term, weightedTerms[i]);
        maxTermWeight = Math.max(maxTermWeight, weightedTerms[i].getWeight());
      }
    }
  }

  /* (non-Javadoc)
   * @see org.apache.lucene.search.highlight.Scorer#init(org.apache.lucene.analysis.TokenStream)
   */
  public TokenStream init(TokenStream tokenStream) {
    termAtt = tokenStream.addAttribute(CharTermAttribute.class);
    return null;
  }

  /*
   * (non-Javadoc)
   * 
   * @see
   * org.apache.lucene.search.highlight.FragmentScorer#startFragment(org.apache
   * .lucene.search.highlight.TextFragment)
   */
  public void startFragment(TextFragment newFragment) {
    uniqueTermsInFragment = new HashSet<String>();
    currentTextFragment = newFragment;
    totalScore = 0;

  }


  /* (non-Javadoc)
   * @see org.apache.lucene.search.highlight.Scorer#getTokenScore()
   */
  public float getTokenScore() {
    String termText = termAtt.toString();

    WeightedTerm queryTerm = termsToFind.get(termText);
    if (queryTerm == null) {
      // not a query term - return
      return 0;
    }
    // found a query term - is it unique in this doc?
    if (!uniqueTermsInFragment.contains(termText)) {
      totalScore += queryTerm.getWeight();
      uniqueTermsInFragment.add(termText);
    }
    return queryTerm.getWeight();
  }


  /* (non-Javadoc)
   * @see org.apache.lucene.search.highlight.Scorer#getFragmentScore()
   */
  public float getFragmentScore() {
    return totalScore;
  }

  /*
   * (non-Javadoc)
   * 
   * @see
   * org.apache.lucene.search.highlight.FragmentScorer#allFragmentsProcessed()
   */
  public void allFragmentsProcessed() {
    // this class has no special operations to perform at end of processing
  }

  /**
   * 
   * @return The highest weighted term (useful for passing to GradientFormatter
   *         to set top end of coloring scale.
   */
  public float getMaxTermWeight() {
    return maxTermWeight;
  }
}

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