DSAnalyzer.java

/*
 * DSAnalyzer.java
 *
 * Version: $Revision: 3705 $
 *
 * Date: $Date: 2009-04-11 17:02:24 +0000 (Sat, 11 Apr 2009) $
 *
 * Copyright (c) 2002-2005, Hewlett-Packard Company and Massachusetts
 * Institute of Technology.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * - Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * - Neither the name of the Hewlett-Packard Company nor the name of the
 * Massachusetts Institute of Technology nor the names of their
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */
package org.dspace.search;

import java.io.Reader;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.PorterStemFilter;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.standard.StandardFilter;
import org.dspace.core.ConfigurationManager;

/**
 * Custom Lucene Analyzer that combines the standard filter, lowercase filter,
 * stemming and stopword filters.
 */
public class DSAnalyzer extends Analyzer
{
    /*
     * An array containing some common words that are not usually useful for
     * searching.
     */
    private static final String[] STOP_WORDS =
    {

    // new stopwords (per MargretB)
            "a", "am", "and", "are", "as", "at", "be", "but", "by", "for",
            "if", "in", "into", "is", "it", "no", "not", "of", "on", "or",
            "the", "to", "was"
    // old stopwords (Lucene default)
    /*
     * "a", "and", "are", "as", "at", "be", "but", "by", "for", "if", "in",
     * "into", "is", "it", "no", "not", "of", "on", "or", "s", "such", "t",
     * "that", "the", "their","then", "there","these", "they", "this", "to",
     * "was", "will", "with"
     */
    };

    /*
     * Stop table
     */
    final static private Set stopSet = StopFilter.makeStopSet(STOP_WORDS);

    /*
     * Create a token stream for this analyzer.
     */
    public final TokenStream tokenStream(String fieldName, final Reader reader)
    {
        TokenStream result = new DSTokenizer(reader);

        result = new StandardFilter(result);
        result = new LowerCaseFilter(result);
        result = new StopFilter(result, stopSet);
        result = new PorterStemFilter(result);

        return result;
    }

    public int getPositionIncrementGap(String fieldName)
    {
        // If it is the default field, or bounded fields is turned off in the config, return the default value
        if ("default".equalsIgnoreCase(fieldName) || !ConfigurationManager.getBooleanProperty("search.boundedfields", false))
            return super.getPositionIncrementGap(fieldName);

        // Not the default field, and we want bounded fields, so return an large gap increment
        return 10;
    }
}