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<Q> {
private final int size;
/**
* Create a TopTermsBooleanQueryRewrite for
* at most <code>size</code> terms.
* <p>
* NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than
* <code>size</code>, 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<ScoreTerm>();
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);
}
}
}