Java tutorial
/* * 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; /** * <p>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}. </p> * * <p><b>NOTE:</b> 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:</p> * * <pre class="prettyprint"> * 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() { * * <em>// ignore scorer</em> * public void setScorer(Scorer scorer) throws IOException { * } * * public void collect(int doc) throws IOException { * bits.set(docBase + doc); * } * * }; * } * * }); * </pre> * * <p>Not all collectors will need to rebase the docID. For * example, a collector that simply counts the total number * of hits would skip it.</p> * * @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(Scorable scorer) throws IOException; /** * Called once for every document matching a query, with the unbased document * number. * <p>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. * <p> * 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; }