/*
 * 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
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 *     http://www.apache.org/licenses/LICENSE-2.0
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 * Unless required by applicable law or agreed to in writing, software
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package org.apache.lucene.analysis.miscellaneous;


import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;

import java.io.IOException;

A token filter for truncating the terms into a specific length. Fixed prefix truncation, as a stemming method, produces good results on Turkish language. It is reported that F5, using first 5 characters, produced best results in Information Retrieval on Turkish Texts
/** * A token filter for truncating the terms into a specific length. * Fixed prefix truncation, as a stemming method, produces good results on Turkish language. * It is reported that F5, using first 5 characters, produced best results in * <a href="http://www.users.muohio.edu/canf/papers/JASIST2008offPrint.pdf"> * Information Retrieval on Turkish Texts</a> */
public final class TruncateTokenFilter extends TokenFilter { private final CharTermAttribute termAttribute = addAttribute(CharTermAttribute.class); private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class); private final int length; public TruncateTokenFilter(TokenStream input, int length) { super(input); if (length < 1) throw new IllegalArgumentException("length parameter must be a positive number: " + length); this.length = length; } @Override public final boolean incrementToken() throws IOException { if (input.incrementToken()) { if (!keywordAttr.isKeyword() && termAttribute.length() > length) termAttribute.setLength(length); return true; } else { return false; } } }