multifilter.java

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/*
 * $RCSfile: MultiFilter.java,v $
 * $Revision: 1.2 $
 * $Date: 2002/05/10 22:19:38 $
 *
 * Copyright (C) 1999-2002 CoolServlets, Inc. All rights reserved.
 *
 * This software is the proprietary information of CoolServlets, Inc.
 * Use is subject to license terms.
 */

package com.jivesoftware.forum.database;

import java.util.*;
import java.io.IOException;

import org.apache.lucene.index.*;
import org.apache.lucene.search.*;

/**
 * A Filter that logically combines multiple other Filters. An arbitrary
 * number of Filter objects can be added to each MultiFilter. When a Query is
 * executed with a MultiFilter, each Document in the HitList must pass every
 * Filter in the MultiFilter filter list.<p>
 *
 * For example, consider a MultiFilter that is created with a FilterX filter
 * and FilterY filter. When a search is executed with the MultiFilter, in order
 * for Document A to appear in the results, it must pass both the FilterX
 * <b>and</b> FilterY filters.<p>
 *
 * If no Filter objects are added to a MultiFilter before it is used in a
 * search, this will have the affect of filtering out all search results.
 *
 * @author Matt Tucker
 */
public class MultiFilter extends org.apache.lucene.search.Filter {

    /**
     * An ArrayList to store the filters that are part of this MultiFilter. We
     * use an ArrayList instead of a Vector for increased performance. If you
     * require JDK1.1 support, change to a Vector.
     */
    private List filterList;

    /**
     * Creates a new MultiFilter.
     */
    public MultiFilter() {
        filterList = new ArrayList();
    }

    /**
     * Creates a new MultiFilter with the specified initial capacity. Providing
     * an initial capacity equal to the size of the eventual MultiFilter size
     * provides a slight performance advantage over letting the MultiFilter
     * grow automatically.
     *
     * @param initialCapacity an initial capacity size for the MultiFilter.
     */
    public MultiFilter(int initialCapacity) {
        filterList = new ArrayList(initialCapacity);
    }

    /**
     * Adds a filter to the MuliFilter filter list.
     *
     * @param filter a Filter to add to the MultiFilter filter list.
     */
    public void add(Filter filter) {
        filterList.add(filter);
    }

    public BitSet bits(IndexReader reader) throws IOException {
        // Iterate through list of filters and apply the boolean AND operation
        // on each bitSet. The AND operator has the affect that only documents
        // that are allowed by every single filter in the filter list will be
        // allowed by this MultiFilter.
        int filterListSize = filterList.size();
        if (filterListSize > 0) {
            BitSet bits = ((Filter)filterList.get(0)).bits(reader);
            for (int i=1; i<filterListSize; i++) {
                bits.and( ((Filter)filterList.get(i)).bits(reader) );
            }
            return bits;
        }
        // There are no filters defined. In this case, we return a new
        // BitSet that will filter out all documents. This is probably the most
        // consistent behavior with the Lucene API. It's also a lot more
        // efficient considering the BitSet implementation.
        else {
            return new BitSet(reader.maxDoc());
        }
    }
}