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What this is

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The source code

package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 java.util.WeakHashMap;
import java.util.BitSet;
import org.apache.lucene.index.IndexReader;

/** Constrains search results to only match those which also match a provided
 * query.  Results are cached, so that searches after the first on the same
 * index using this filter are much faster.
 *
 * 

This could be used, for example, with a {@link RangeQuery} on a suitably * formatted date field to implement date filtering. One could re-use a single * QueryFilter that matches, e.g., only documents modified within the last * week. The QueryFilter and RangeQuery would only need to be reconstructed * once per day. * * @version $Id: QueryFilter.java,v 1.6 2004/05/08 19:54:12 ehatcher Exp $ */ public class QueryFilter extends Filter { private Query query; private transient WeakHashMap cache = null; /** Constructs a filter which only matches documents matching * query. */ public QueryFilter(Query query) { this.query = query; } public BitSet bits(IndexReader reader) throws IOException { if (cache == null) { cache = new WeakHashMap(); } synchronized (cache) { // check cache BitSet cached = (BitSet) cache.get(reader); if (cached != null) { return cached; } } final BitSet bits = new BitSet(reader.maxDoc()); new IndexSearcher(reader).search(query, new HitCollector() { public final void collect(int doc, float score) { bits.set(doc); // set bit for hit } }); synchronized (cache) { // update cache cache.put(reader, bits); } return bits; } public String toString() { return "QueryFilter("+query+")"; } }

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