org.apache.lucene.search.highlight.QueryTermExtractor.java Source code

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Here is the source code for org.apache.lucene.search.highlight.QueryTermExtractor.java

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/*
 * 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.
 */
package org.apache.lucene.search.highlight;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
import java.util.function.Predicate;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.MultiReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.BoostQuery;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryVisitor;

/**
 * Utility class used to extract the terms used in a query, plus any weights.
 * This class will not find terms for MultiTermQuery, TermRangeQuery and PrefixQuery classes
 * so the caller must pass a rewritten query (see Query.rewrite) to obtain a list of 
 * expanded terms. 
 * 
 */
public final class QueryTermExtractor {

    /** for term extraction */
    private static final IndexSearcher EMPTY_INDEXSEARCHER;
    static {
        try {
            IndexReader emptyReader = new MultiReader();
            EMPTY_INDEXSEARCHER = new IndexSearcher(emptyReader);
            EMPTY_INDEXSEARCHER.setQueryCache(null);
        } catch (IOException bogus) {
            throw new RuntimeException(bogus);
        }
    }

    /**
     * Extracts all terms texts of a given Query into an array of WeightedTerms
     *
     * @param query      Query to extract term texts from
     * @return an array of the terms used in a query, plus their weights.
     */
    public static final WeightedTerm[] getTerms(Query query) {
        return getTerms(query, false);
    }

    /**
     * Extracts all terms texts of a given Query into an array of WeightedTerms
     *
     * @param query      Query to extract term texts from
     * @param reader used to compute IDF which can be used to a) score selected fragments better
     * b) use graded highlights eg changing intensity of font color
     * @param fieldName the field on which Inverse Document Frequency (IDF) calculations are based
     * @return an array of the terms used in a query, plus their weights.
     */
    public static final WeightedTerm[] getIdfWeightedTerms(Query query, IndexReader reader, String fieldName) {
        WeightedTerm[] terms = getTerms(query, false, fieldName);
        int totalNumDocs = reader.maxDoc();
        for (int i = 0; i < terms.length; i++) {
            try {
                int docFreq = reader.docFreq(new Term(fieldName, terms[i].term));
                //IDF algorithm taken from ClassicSimilarity class
                float idf = (float) (Math.log(totalNumDocs / (double) (docFreq + 1)) + 1.0);
                terms[i].weight *= idf;
            } catch (IOException e) {
                //ignore
            }
        }
        return terms;
    }

    /**
     * Extracts all terms texts of a given Query into an array of WeightedTerms
     *
     * @param query      Query to extract term texts from
     * @param prohibited <code>true</code> to extract "prohibited" terms, too
     * @param fieldName  The fieldName used to filter query terms
     * @return an array of the terms used in a query, plus their weights.
     */
    public static WeightedTerm[] getTerms(Query query, boolean prohibited, String fieldName) {
        HashSet<WeightedTerm> terms = new HashSet<>();
        Predicate<String> fieldSelector = fieldName == null ? f -> true : fieldName::equals;
        query.visit(new BoostedTermExtractor(1, terms, prohibited, fieldSelector));
        return terms.toArray(new WeightedTerm[0]);
    }

    /**
     * Extracts all terms texts of a given Query into an array of WeightedTerms
     *
     * @param query      Query to extract term texts from
     * @param prohibited <code>true</code> to extract "prohibited" terms, too
     * @return an array of the terms used in a query, plus their weights.
     */
    public static final WeightedTerm[] getTerms(Query query, boolean prohibited) {
        return getTerms(query, prohibited, null);
    }

    private static class BoostedTermExtractor extends QueryVisitor {

        final float boost;
        final Set<WeightedTerm> terms;
        final boolean includeProhibited;
        final Predicate<String> fieldSelector;

        private BoostedTermExtractor(float boost, Set<WeightedTerm> terms, boolean includeProhibited,
                Predicate<String> fieldSelector) {
            this.boost = boost;
            this.terms = terms;
            this.includeProhibited = includeProhibited;
            this.fieldSelector = fieldSelector;
        }

        @Override
        public boolean acceptField(String field) {
            return fieldSelector.test(field);
        }

        @Override
        public void consumeTerms(Query query, Term... terms) {
            for (Term term : terms) {
                this.terms.add(new WeightedTerm(boost, term.text()));
            }
        }

        @Override
        public QueryVisitor getSubVisitor(BooleanClause.Occur occur, Query parent) {
            if (parent instanceof BoostQuery) {
                float newboost = boost * ((BoostQuery) parent).getBoost();
                return new BoostedTermExtractor(newboost, terms, includeProhibited, fieldSelector);
            }
            if (occur == BooleanClause.Occur.MUST_NOT && includeProhibited == false) {
                return QueryVisitor.EMPTY_VISITOR;
            }
            return this;
        }

    }

}