org.apache.lucene.search.LeafCollector Maven / Gradle / Ivy
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;
/**
* Collector decouples the score from the collected doc:
* the score computation is skipped entirely if it's not
* needed. Collectors that do need the score should
* implement the {@link #setScorer} method, to hold onto the
* passed {@link Scorer} instance, and call {@link
* Scorer#score()} within the collect method to compute the
* current hit's score. If your collector may request the
* score for a single hit multiple times, you should use
* {@link ScoreCachingWrappingScorer}.
*
* NOTE: The doc that is passed to the collect
* method is relative to the current reader. If your
* collector needs to resolve this to the docID space of the
* Multi*Reader, you must re-base it by recording the
* docBase from the most recent setNextReader call. Here's
* a simple example showing how to collect docIDs into a
* BitSet:
*
*
* IndexSearcher searcher = new IndexSearcher(indexReader);
* final BitSet bits = new BitSet(indexReader.maxDoc());
* searcher.search(query, new Collector() {
*
* public LeafCollector getLeafCollector(LeafReaderContext context)
* throws IOException {
* final int docBase = context.docBase;
* return new LeafCollector() {
*
* // ignore scorer
* public void setScorer(Scorer scorer) throws IOException {
* }
*
* public void collect(int doc) throws IOException {
* bits.set(docBase + doc);
* }
*
* };
* }
*
* });
*
*
* Not all collectors will need to rebase the docID. For
* example, a collector that simply counts the total number
* of hits would skip it.
*
* @lucene.experimental
*/
public interface LeafCollector {
/**
* Called before successive calls to {@link #collect(int)}. Implementations
* that need the score of the current document (passed-in to
* {@link #collect(int)}), should save the passed-in Scorer and call
* scorer.score() when needed.
*/
void setScorer(Scorer scorer) throws IOException;
/**
* Called once for every document matching a query, with the unbased document
* number.
* Note: The collection of the current segment can be terminated by throwing
* a {@link CollectionTerminatedException}. In this case, the last docs of the
* current {@link org.apache.lucene.index.LeafReaderContext} will be skipped and {@link IndexSearcher}
* will swallow the exception and continue collection with the next leaf.
*
* Note: This is called in an inner search loop. For good search performance,
* implementations of this method should not call {@link IndexSearcher#doc(int)} or
* {@link org.apache.lucene.index.IndexReader#document(int)} on every hit.
* Doing so can slow searches by an order of magnitude or more.
*/
void collect(int doc) throws IOException;
}