--- /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 org.apache.lucene.util.PriorityQueue;
+
+/**
+ * A base class for all collectors that return a {@link TopDocs} output. This
+ * collector allows easy extension by providing a single constructor which
+ * accepts a {@link PriorityQueue} as well as protected members for that
+ * priority queue and a counter of the number of total hits.<br>
+ * Extending classes can override any of the methods to provide their own
+ * implementation, as well as avoid the use of the priority queue entirely by
+ * passing null to {@link #TopDocsCollector(PriorityQueue)}. In that case
+ * however, you might want to consider overriding all methods, in order to avoid
+ * a NullPointerException.
+ */
+public abstract class TopDocsCollector<T extends ScoreDoc> extends Collector {
+
+ // This is used in case topDocs() is called with illegal parameters, or there
+ // simply aren't (enough) results.
+ protected static final TopDocs EMPTY_TOPDOCS = new TopDocs(0, new ScoreDoc[0], Float.NaN);
+
+ /**
+ * The priority queue which holds the top documents. Note that different
+ * implementations of PriorityQueue give different meaning to 'top documents'.
+ * HitQueue for example aggregates the top scoring documents, while other PQ
+ * implementations may hold documents sorted by other criteria.
+ */
+ protected PriorityQueue<T> pq;
+
+ /** The total number of documents that the collector encountered. */
+ protected int totalHits;
+
+ protected TopDocsCollector(PriorityQueue<T> pq) {
+ this.pq = pq;
+ }
+
+ /**
+ * Populates the results array with the ScoreDoc instances. This can be
+ * overridden in case a different ScoreDoc type should be returned.
+ */
+ protected void populateResults(ScoreDoc[] results, int howMany) {
+ for (int i = howMany - 1; i >= 0; i--) {
+ results[i] = pq.pop();
+ }
+ }
+
+ /**
+ * Returns a {@link TopDocs} instance containing the given results. If
+ * <code>results</code> is null it means there are no results to return,
+ * either because there were 0 calls to collect() or because the arguments to
+ * topDocs were invalid.
+ */
+ protected TopDocs newTopDocs(ScoreDoc[] results, int start) {
+ return results == null ? EMPTY_TOPDOCS : new TopDocs(totalHits, results);
+ }
+
+ /** The total number of documents that matched this query. */
+ public int getTotalHits() {
+ return totalHits;
+ }
+
+ /** The number of valid PQ entries */
+ protected int topDocsSize() {
+ // In case pq was populated with sentinel values, there might be less
+ // results than pq.size(). Therefore return all results until either
+ // pq.size() or totalHits.
+ return totalHits < pq.size() ? totalHits : pq.size();
+ }
+
+ /** Returns the top docs that were collected by this collector. */
+ public TopDocs topDocs() {
+ // In case pq was populated with sentinel values, there might be less
+ // results than pq.size(). Therefore return all results until either
+ // pq.size() or totalHits.
+ return topDocs(0, topDocsSize());
+ }
+
+ /**
+ * Returns the documents in the rage [start .. pq.size()) that were collected
+ * by this collector. Note that if start >= pq.size(), an empty TopDocs is
+ * returned.<br>
+ * This method is convenient to call if the application always asks for the
+ * last results, starting from the last 'page'.<br>
+ * <b>NOTE:</b> you cannot call this method more than once for each search
+ * execution. If you need to call it more than once, passing each time a
+ * different <code>start</code>, you should call {@link #topDocs()} and work
+ * with the returned {@link TopDocs} object, which will contain all the
+ * results this search execution collected.
+ */
+ public TopDocs topDocs(int start) {
+ // In case pq was populated with sentinel values, there might be less
+ // results than pq.size(). Therefore return all results until either
+ // pq.size() or totalHits.
+ return topDocs(start, topDocsSize());
+ }
+
+ /**
+ * Returns the documents in the rage [start .. start+howMany) that were
+ * collected by this collector. Note that if start >= pq.size(), an empty
+ * TopDocs is returned, and if pq.size() - start < howMany, then only the
+ * available documents in [start .. pq.size()) are returned.<br>
+ * This method is useful to call in case pagination of search results is
+ * allowed by the search application, as well as it attempts to optimize the
+ * memory used by allocating only as much as requested by howMany.<br>
+ * <b>NOTE:</b> you cannot call this method more than once for each search
+ * execution. If you need to call it more than once, passing each time a
+ * different range, you should call {@link #topDocs()} and work with the
+ * returned {@link TopDocs} object, which will contain all the results this
+ * search execution collected.
+ */
+ public TopDocs topDocs(int start, int howMany) {
+
+ // In case pq was populated with sentinel values, there might be less
+ // results than pq.size(). Therefore return all results until either
+ // pq.size() or totalHits.
+ int size = topDocsSize();
+
+ // Don't bother to throw an exception, just return an empty TopDocs in case
+ // the parameters are invalid or out of range.
+ // TODO: shouldn't we throw IAE if apps give bad params here so they dont
+ // have sneaky silent bugs?
+ if (start < 0 || start >= size || howMany <= 0) {
+ return newTopDocs(null, start);
+ }
+
+ // We know that start < pqsize, so just fix howMany.
+ howMany = Math.min(size - start, howMany);
+ ScoreDoc[] results = new ScoreDoc[howMany];
+
+ // pq's pop() returns the 'least' element in the queue, therefore need
+ // to discard the first ones, until we reach the requested range.
+ // Note that this loop will usually not be executed, since the common usage
+ // should be that the caller asks for the last howMany results. However it's
+ // needed here for completeness.
+ for (int i = pq.size() - start - howMany; i > 0; i--) { pq.pop(); }
+
+ // Get the requested results from pq.
+ populateResults(results, howMany);
+
+ return newTopDocs(results, start);
+ }
+
+}
fnp / pylucene.git / blobdiff