| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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 org.apache.lucene.analysis.de; |
| |
| |
| import java.io.IOException; |
| |
| import org.apache.lucene.analysis.TokenFilter; |
| import org.apache.lucene.analysis.TokenStream; |
| import org.apache.lucene.analysis.tokenattributes.CharTermAttribute; |
| import org.apache.lucene.analysis.util.StemmerUtil; |
| |
| /** |
| * Normalizes German characters according to the heuristics |
| * of the <a href="http://snowball.tartarus.org/algorithms/german2/stemmer.html"> |
| * German2 snowball algorithm</a>. |
| * It allows for the fact that ä, ö and ü are sometimes written as ae, oe and ue. |
| * <ul> |
| * <li> 'ß' is replaced by 'ss' |
| * <li> 'ä', 'ö', 'ü' are replaced by 'a', 'o', 'u', respectively. |
| * <li> 'ae' and 'oe' are replaced by 'a', and 'o', respectively. |
| * <li> 'ue' is replaced by 'u', when not following a vowel or q. |
| * </ul> |
| * This is useful if you want this normalization without using |
| * the German2 stemmer, or perhaps no stemming at all. |
| */ |
| public final class GermanNormalizationFilter extends TokenFilter { |
| // FSM with 3 states: |
| private static final int N = 0; /* ordinary state */ |
| private static final int V = 1; /* stops 'u' from entering umlaut state */ |
| private static final int U = 2; /* umlaut state, allows e-deletion */ |
| |
| private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class); |
| |
| public GermanNormalizationFilter(TokenStream input) { |
| super(input); |
| } |
| |
| @Override |
| public boolean incrementToken() throws IOException { |
| if (input.incrementToken()) { |
| int state = N; |
| char buffer[] = termAtt.buffer(); |
| int length = termAtt.length(); |
| for (int i = 0; i < length; i++) { |
| final char c = buffer[i]; |
| switch(c) { |
| case 'a': |
| case 'o': |
| state = U; |
| break; |
| case 'u': |
| state = (state == N) ? U : V; |
| break; |
| case 'e': |
| if (state == U) |
| length = StemmerUtil.delete(buffer, i--, length); |
| state = V; |
| break; |
| case 'i': |
| case 'q': |
| case 'y': |
| state = V; |
| break; |
| case 'ä': |
| buffer[i] = 'a'; |
| state = V; |
| break; |
| case 'ö': |
| buffer[i] = 'o'; |
| state = V; |
| break; |
| case 'ü': |
| buffer[i] = 'u'; |
| state = V; |
| break; |
| case 'ß': |
| buffer[i++] = 's'; |
| buffer = termAtt.resizeBuffer(1+length); |
| if (i < length) |
| System.arraycopy(buffer, i, buffer, i+1, (length-i)); |
| buffer[i] = 's'; |
| length++; |
| state = N; |
| break; |
| default: |
| state = N; |
| } |
| } |
| termAtt.setLength(length); |
| return true; |
| } else { |
| return false; |
| } |
| } |
| } |