www.pudn.com > dlucene-1.4.3-src.rar > RussianStemFilter.java

package org.apache.lucene.analysis.ru; 
 
/** 
 * 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 org.apache.lucene.analysis.Token; 
import org.apache.lucene.analysis.TokenFilter; 
import org.apache.lucene.analysis.TokenStream; 
import java.io.IOException; 
 
/** 
 * A filter that stems Russian words. The implementation was inspired by GermanStemFilter. 
 * The input should be filtered by RussianLowerCaseFilter before passing it to RussianStemFilter , 
 * because RussianStemFilter only works  with lowercase part of any "russian" charset. 
 * 
 * @author    Boris Okner, b.okner@rogers.com 
 * @version   $Id: RussianStemFilter.java,v 1.5 2004/03/29 22:48:01 cutting Exp $ 
 */ 
public final class RussianStemFilter extends TokenFilter 
{ 
    /** 
     * The actual token in the input stream. 
     */ 
    private Token token = null; 
    private RussianStemmer stemmer = null; 
 
    public RussianStemFilter(TokenStream in, char[] charset) 
    { 
        super(in); 
        stemmer = new RussianStemmer(charset); 
    } 
 
    /** 
     * @return  Returns the next token in the stream, or null at EOS 
     */ 
    public final Token next() throws IOException 
    { 
        if ((token = input.next()) == null) 
        { 
            return null; 
        } 
        else 
        { 
            String s = stemmer.stem(token.termText()); 
            if (!s.equals(token.termText())) 
            { 
                return new Token(s, token.startOffset(), token.endOffset(), 
                    token.type()); 
            } 
            return token; 
        } 
    } 
 
    /** 
     * Set a alternative/custom RussianStemmer for this filter. 
     */ 
    public void setStemmer(RussianStemmer stemmer) 
    { 
        if (stemmer != null) 
        { 
            this.stemmer = stemmer; 
        } 
    } 
}