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Lucene example source code file (BoostingQuery.java)

This example Lucene source code file (BoostingQuery.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, boostingquery, boostingquery, defaultsimilarity, io, ioexception, override, override, query, query, similarity, string

The Lucene BoostingQuery.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.search.BooleanQuery;
import org.apache.lucene.search.DefaultSimilarity;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.Searcher;
import org.apache.lucene.search.Similarity;
/**
 * The BoostingQuery class can be used to effectively demote results that match a given query. 
 * Unlike the "NOT" clause, this still selects documents that contain undesirable terms, 
 * but reduces their overall score:
 *
 *     Query balancedQuery = new BoostingQuery(positiveQuery, negativeQuery, 0.01f);
 * In this scenario the positiveQuery contains the mandatory, desirable criteria which is used to 
 * select all matching documents, and the negativeQuery contains the undesirable elements which 
 * are simply used to lessen the scores. Documents that match the negativeQuery have their score 
 * multiplied by the supplied "boost" parameter, so this should be less than 1 to achieve a 
 * demoting effect
 * 
 * This code was originally made available here: [WWW] http://marc.theaimsgroup.com/?l=lucene-user&m=108058407130459&w=2
 * and is documented here: http://wiki.apache.org/lucene-java/CommunityContributions
 */
public class BoostingQuery extends Query {
    private float boost;                            // the amount to boost by
    private Query match;                            // query to match
    private Query context;                          // boost when matches too

    public BoostingQuery(Query match, Query context, float boost) {
      this.match = match;
      this.context = (Query)context.clone();        // clone before boost
      this.boost = boost;

      this.context.setBoost(0.0f);                      // ignore context-only matches
    }

    @Override
    public Query rewrite(IndexReader reader) throws IOException {
      BooleanQuery result = new BooleanQuery() {

        @Override
        public Similarity getSimilarity(Searcher searcher) {
          return new DefaultSimilarity() {

            @Override
            public float coord(int overlap, int max) {
              switch (overlap) {

              case 1:                               // matched only one clause
                return 1.0f;                        // use the score as-is

              case 2:                               // matched both clauses
                return boost;                       // multiply by boost

              default:
                return 0.0f;
                
              }
            }
          };
        }
      };

      result.add(match, BooleanClause.Occur.MUST);
      result.add(context, BooleanClause.Occur.SHOULD);

      return result;
    }

    @Override
    public int hashCode() {
      final int prime = 31;
      int result = 1;
      result = prime * result + Float.floatToIntBits(boost);
      result = prime * result + ((context == null) ? 0 : context.hashCode());
      result = prime * result + ((match == null) ? 0 : match.hashCode());
      return result;
    }

    @Override
    public boolean equals(Object obj) {
      if (this == obj)
        return true;
      if (obj == null)
        return false;
      if (getClass() != obj.getClass())
        return false;
      BoostingQuery other = (BoostingQuery) obj;
      if (Float.floatToIntBits(boost) != Float.floatToIntBits(other.boost))
        return false;
      if (context == null) {
        if (other.context != null)
          return false;
      } else if (!context.equals(other.context))
        return false;
      if (match == null) {
        if (other.match != null)
          return false;
      } else if (!match.equals(other.match))
        return false;
      return true;
    }

    @Override
    public String toString(String field) {
      return match.toString(field) + "/" + context.toString(field);
    }
  }

Other Lucene examples (source code examples)

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



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