org.apache.lucene.search.BoostQuery.java Source code

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Here is the source code for org.apache.lucene.search.BoostQuery.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;

import java.io.IOException;
import java.util.Objects;

import org.apache.lucene.index.IndexReader;

/**
 * A {@link Query} wrapper that allows to give a boost to the wrapped query.
 * Boost values that are less than one will give less importance to this
 * query compared to other ones while values that are greater than one will
 * give more importance to the scores returned by this query.
 *
 * More complex boosts can be applied by using FunctionScoreQuery in the
 * lucene-queries module
 */
public final class BoostQuery extends Query {

    private final Query query;
    private final float boost;

    /** Sole constructor: wrap {@code query} in such a way that the produced
     *  scores will be boosted by {@code boost}. */
    public BoostQuery(Query query, float boost) {
        this.query = Objects.requireNonNull(query);
        if (Float.isFinite(boost) == false || Float.compare(boost, 0f) < 0) {
            throw new IllegalArgumentException("boost must be a positive float, got " + boost);
        }
        this.boost = boost;
    }

    /**
     * Return the wrapped {@link Query}.
     */
    public Query getQuery() {
        return query;
    }

    /**
     * Return the applied boost.
     */
    public float getBoost() {
        return boost;
    }

    @Override
    public boolean equals(Object other) {
        return sameClassAs(other) && equalsTo(getClass().cast(other));
    }

    private boolean equalsTo(BoostQuery other) {
        return query.equals(other.query) && Float.floatToIntBits(boost) == Float.floatToIntBits(other.boost);
    }

    @Override
    public int hashCode() {
        int h = classHash();
        h = 31 * h + query.hashCode();
        h = 31 * h + Float.floatToIntBits(boost);
        return h;
    }

    @Override
    public Query rewrite(IndexReader reader) throws IOException {
        final Query rewritten = query.rewrite(reader);

        if (boost == 1f) {
            return rewritten;
        }

        if (rewritten.getClass() == BoostQuery.class) {
            BoostQuery in = (BoostQuery) rewritten;
            return new BoostQuery(in.query, boost * in.boost);
        }

        if (boost == 0f && rewritten.getClass() != ConstantScoreQuery.class) {
            // so that we pass needScores=false
            return new BoostQuery(new ConstantScoreQuery(rewritten), 0f);
        }

        if (query != rewritten) {
            return new BoostQuery(rewritten, boost);
        }

        return super.rewrite(reader);
    }

    @Override
    public void visit(QueryVisitor visitor) {
        query.visit(visitor.getSubVisitor(BooleanClause.Occur.MUST, this));
    }

    @Override
    public String toString(String field) {
        StringBuilder builder = new StringBuilder();
        builder.append("(");
        builder.append(query.toString(field));
        builder.append(")");
        builder.append("^");
        builder.append(boost);
        return builder.toString();
    }

    @Override
    public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException {
        return query.createWeight(searcher, scoreMode, BoostQuery.this.boost * boost);
    }

}