fieldfilter.java

这是学习Java必须读懂两套源代码

/**
 * FieldFilter.java
 *
 * Copyright (c) 2000 Douglass R. Cutting.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package com.Yasna.forum.database;

import java.util.BitSet;
import java.io.IOException;

import com.lucene.index.Term;
import com.lucene.index.TermDocs;
import com.lucene.index.IndexReader;

/**
 * A Filter that restricts search results to Documents that match a specified
 * Field value.
 *
 * For example, suppose you create a search index to make your catalog of widgets
 * searchable. When indexing, you add a field to each Document called "color"
 * that has one of the following values: "blue", "green", "yellow", or "red".
 * Now suppose that a user is executing a query but only wants to see green
 * widgets in the results. The following code snippet yields that behavior:
 * <pre>
 *     //In this example, we assume the Searcher and Query are already defined.
 *     //Define a FieldFilter to only show green colored widgets.
 *     Field myFilter = new FieldFilter("color", "green");
 *     Hits queryResults = mySearcher.execute(myQuery, myFilter);
 * </pre>
 *
 * @author Matt Tucker ([e-mail])
 */
public class FieldFilter extends com.lucene.search.Filter {

    private String field;
    private String value;
    private Term searchTerm;

    /**
     * Creates a new field filter. The name of the field and the value to filter
     * on are specified. In order for a Document to pass this filter, it must:
     * <ol>
     *      <li>The given field must exist in the document.
     *      <li>The field value in the Document must exactly match the given
     *          value.</ol>
     *
     * @param field the name of the field to filter on.
     * @param value the value of the field that search results must match.
     */
    public FieldFilter(String field, String value) {
        this.field = field;
        this.value = value;
        searchTerm = new Term(field, value);
    }

    public BitSet bits(IndexReader reader) throws IOException {
        //Create a new BitSet with a capacity equal to the size of the index.
        BitSet bits = new BitSet(reader.maxDoc());
        //Get an enumeration of all the documents that match the specified field
        //value.
        TermDocs matchingDocs = reader.termDocs(searchTerm);
        try {
            while(matchingDocs.next()) {
                bits.set(matchingDocs.doc());
            }
        }
        finally {
            if (matchingDocs != null) {
                matchingDocs.close();
            }
        }
        return bits;
    }
}