--- /dev/null
+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 org.apache.lucene.index.IndexReader;
+
+/**
+ * <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 Collector.
+ * 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>
+ *
+ * <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>
+ * Searcher searcher = new IndexSearcher(indexReader);
+ * final BitSet bits = new BitSet(indexReader.maxDoc());
+ * searcher.search(query, new Collector() {
+ * private int docBase;
+ *
+ * <em>// ignore scorer</em>
+ * public void setScorer(Scorer scorer) {
+ * }
+ *
+ * <em>// accept docs out of order (for a BitSet it doesn't matter)</em>
+ * public boolean acceptsDocsOutOfOrder() {
+ * return true;
+ * }
+ *
+ * public void collect(int doc) {
+ * bits.set(doc + docBase);
+ * }
+ *
+ * public void setNextReader(IndexReader reader, int docBase) {
+ * this.docBase = docBase;
+ * }
+ * });
+ * </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>
+ *
+ * <p><b>NOTE:</b> Prior to 2.9, Lucene silently filtered
+ * out hits with score <= 0. As of 2.9, the core Collectors
+ * no longer do that. It's very unusual to have such hits
+ * (a negative query boost, or function query returning
+ * negative custom scores, could cause it to happen). If
+ * you need that behavior, use {@link
+ * PositiveScoresOnlyCollector}.</p>
+ *
+ * @lucene.experimental
+ *
+ * @since 2.9
+ */
+public abstract class Collector {
+
+ /**
+ * 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.
+ */
+ public abstract void setScorer(Scorer scorer) throws IOException;
+
+ /**
+ * Called once for every document matching a query, with the unbased document
+ * number.
+ *
+ * <p>
+ * Note: This is called in an inner search loop. For good search performance,
+ * implementations of this method should not call {@link Searcher#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.
+ */
+ public abstract void collect(int doc) throws IOException;
+
+ /**
+ * Called before collecting from each IndexReader. All doc ids in
+ * {@link #collect(int)} will correspond to reader.
+ *
+ * Add docBase to the current IndexReaders internal document id to re-base ids
+ * in {@link #collect(int)}.
+ *
+ * @param reader
+ * next IndexReader
+ * @param docBase
+ */
+ public abstract void setNextReader(IndexReader reader, int docBase) throws IOException;
+
+ /**
+ * Return <code>true</code> if this collector does not
+ * require the matching docIDs to be delivered in int sort
+ * order (smallest to largest) to {@link #collect}.
+ *
+ * <p> Most Lucene Query implementations will visit
+ * matching docIDs in order. However, some queries
+ * (currently limited to certain cases of {@link
+ * BooleanQuery}) can achieve faster searching if the
+ * <code>Collector</code> allows them to deliver the
+ * docIDs out of order.</p>
+ *
+ * <p> Many collectors don't mind getting docIDs out of
+ * order, so it's important to return <code>true</code>
+ * here.
+ */
+ public abstract boolean acceptsDocsOutOfOrder();
+
+}
fnp / pylucene.git / blobdiff