/*
* 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 org.apache.lucene.index.LeafReaderContext;
/**
* <p>Expert: Collectors are primarily meant to be used to
* gather raw results from a search, and implement sorting
* or custom result filtering, collation, etc. </p>
*
* <p>Lucene's core collectors are derived from {@link Collector}
* and {@link SimpleCollector}. Likely your application can
* use one of these classes, or subclass {@link TopDocsCollector},
* instead of implementing Collector directly:
*
* <ul>
*
* <li>{@link TopDocsCollector} is an abstract base class
* that assumes you will retrieve the top N docs,
* according to some criteria, after collection is
* done. </li>
*
* <li>{@link TopScoreDocCollector} is a concrete subclass
* {@link TopDocsCollector} and sorts according to score +
* docID. This is used internally by the {@link
* IndexSearcher} search methods that do not take an
* explicit {@link Sort}. It is likely the most frequently
* used collector.</li>
*
* <li>{@link TopFieldCollector} subclasses {@link
* TopDocsCollector} and sorts according to a specified
* {@link Sort} object (sort by field). This is used
* internally by the {@link IndexSearcher} search methods
* that take an explicit {@link Sort}.
*
* <li>{@link TimeLimitingCollector}, which wraps any other
* Collector and aborts the search if it's taken too much
* time.</li>
*
* <li>{@link PositiveScoresOnlyCollector} wraps any other
* Collector and prevents collection of hits whose score
* is <= 0.0</li>
*
* </ul>
*
* @lucene.experimental
*/
public interface Collector {
/**
* Create a new {@link LeafCollector collector} to collect the given context.
*
* @param context
* next atomic reader context
*/
LeafCollector getLeafCollector(LeafReaderContext context) throws IOException;
/**
* Indicates if document scores are needed by this collector.
*
* @return {@code true} if scores are needed.
*/
boolean needsScores();
}