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Lucene example source code file (TopTermsRewrite.java)

This example Lucene source code file (TopTermsRewrite.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

indexreader, io, ioexception, override, override, priorityqueue, q, q, scoreterm, scoreterm, term, termcollectingrewrite, termcollector, toptermsrewrite, toptermsrewrite, util

The Lucene TopTermsRewrite.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 java.util.PriorityQueue;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

/**
 * Base rewrite method for collecting only the top terms
 * via a priority queue.
 * @lucene.internal Only public to be accessible by spans package.
 */
public abstract class TopTermsRewrite<Q extends Query> extends TermCollectingRewrite {

  private final int size;
  
  /** 
   * Create a TopTermsBooleanQueryRewrite for 
   * at most <code>size terms.
   * <p>
   * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
   * <code>size, then it will be used instead. 
   */
  public TopTermsRewrite(int size) {
    this.size = size;
  }
  
  /** return the maximum priority queue size */
  public int getSize() {
    return size;
  }
  
  /** return the maximum size of the priority queue (for boolean rewrites this is BooleanQuery#getMaxClauseCount). */
  protected abstract int getMaxSize();
  
  @Override
  public Q rewrite(final IndexReader reader, final MultiTermQuery query) throws IOException {
    final int maxSize = Math.min(size, getMaxSize());
    final PriorityQueue<ScoreTerm> stQueue = new PriorityQueue();
    collectTerms(reader, query, new TermCollector() {
      public boolean collect(Term t, float boost) {
        // ignore uncompetitive hits
        if (stQueue.size() >= maxSize && boost <= stQueue.peek().boost)
          return true;
        // add new entry in PQ
        st.term = t;
        st.boost = boost;
        stQueue.offer(st);
        // possibly drop entries from queue
        st = (stQueue.size() > maxSize) ? stQueue.poll() : new ScoreTerm();
        return true;
      }
      
      // reusable instance
      private ScoreTerm st = new ScoreTerm();
    });
    
    final Q q = getTopLevelQuery();
    for (final ScoreTerm st : stQueue) {
      addClause(q, st.term, query.getBoost() * st.boost); // add to query
    }
    query.incTotalNumberOfTerms(stQueue.size());
    
    return q;
  }

  @Override
  public int hashCode() {
    return 31 * size;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj) return true;
    if (obj == null) return false;
    if (getClass() != obj.getClass()) return false;
    final TopTermsRewrite other = (TopTermsRewrite) obj;
    if (size != other.size) return false;
    return true;
  }
  
  private static class ScoreTerm implements Comparable<ScoreTerm> {
    public Term term;
    public float boost;
    
    public int compareTo(ScoreTerm other) {
      if (this.boost == other.boost)
        return other.term.compareTo(this.term);
      else
        return Float.compare(this.boost, other.boost);
    }
  }
  
}

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