nl.inl.blacklab.filter.TranscribeGermanAccentsFilter.java Source code

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Here is the source code for nl.inl.blacklab.filter.TranscribeGermanAccentsFilter.java

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/*******************************************************************************
 * Copyright (c) 2010, 2012 Institute for Dutch Lexicology
 *
 * 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.
 *******************************************************************************/
package nl.inl.blacklab.filter;

import java.io.IOException;
import java.io.StringReader;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.core.WhitespaceTokenizer;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.util.Version;

/**
 * Transcribes words with special and accented characters according to rules for German.
 *
 * Adapted from sample code from Lucene in Action, 2nd ed.
 */
public class TranscribeGermanAccentsFilter extends TokenFilter {
    /**
     * Transcribe German accents
     * @param input string to process
     * @return the string with accents transcribed to ASCII characters
     */
    public static String process(String input) {
        // NOTE: could be sped up by looping over a char[]
        input = input.replaceAll("", "oe");
        input = input.replaceAll("", "ue");
        input = input.replaceAll("", "ae");
        input = input.replaceAll("", "Oe");
        input = input.replaceAll("", "Ue");
        input = input.replaceAll("", "Ae");
        input = input.replaceAll("", "ss");
        return input;
    }

    /**
     * Test program
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        TokenStream ts = new WhitespaceTokenizer(Version.LUCENE_42,
                new StringReader("Aachen Dsseldorf Kln Berlin sterreich"));
        try {
            ts = new TranscribeGermanAccentsFilter(ts);

            CharTermAttribute term = ts.addAttribute(CharTermAttribute.class);
            while (ts.incrementToken()) {
                System.out.println(new String(term.buffer(), 0, term.length()));
            }
        } finally {
            ts.close();
        }
    }

    private CharTermAttribute termAtt;

    /**
     * @param input input token stream
     */
    public TranscribeGermanAccentsFilter(TokenStream input) {
        super(input);
        termAtt = addAttribute(CharTermAttribute.class);
    }

    @Override
    public boolean incrementToken() throws IOException {
        if (input.incrementToken()) {
            String t = new String(termAtt.buffer(), 0, termAtt.length());
            t = process(t);
            termAtt.copyBuffer(t.toCharArray(), 0, t.length());
            return true;
        }
        return false;
    }

}