Lucene example source code file (GreekLowerCaseFilter.java)

This example Lucene source code file (GreekLowerCaseFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

characterutils, characterutils, chartermattribute, deprecated, greeklowercasefilter, greeklowercasefilter, io, ioexception, ioexception, override, tokenfilter, tokenstream, tokenstream

The Lucene GreekLowerCaseFilter.java source code

package org.apache.lucene.analysis.el;

/**
 * Copyright 2005 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 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.util.CharacterUtils;
import org.apache.lucene.util.Version;

/**
 * Normalizes token text to lower case, removes some Greek diacritics,
 * and standardizes final sigma to sigma. 
 * <a name="version"/>
 * <p>You must specify the required {@link Version}
 * compatibility when creating GreekLowerCaseFilter:
 * <ul>
 *   <li> As of 3.1, supplementary characters are properly lowercased.
 * </ul>
 */
public final class GreekLowerCaseFilter extends TokenFilter {
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final CharacterUtils charUtils;

  /** @deprecated Use {@link #GreekLowerCaseFilter(Version, TokenStream)} instead. */
  @Deprecated
  public GreekLowerCaseFilter(TokenStream in) {
    this(Version.LUCENE_30, in);
  }
  
  /**
   * Create a GreekLowerCaseFilter that normalizes Greek token text.
   * 
   * @param matchVersion Lucene compatibility version, 
   *   See <a href="#version">above
   * @param in TokenStream to filter
   */
  public GreekLowerCaseFilter(Version matchVersion, TokenStream in) {
    super(in);
    this.charUtils = CharacterUtils.getInstance(matchVersion);
  }
  
  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      char[] chArray = termAtt.buffer();
      int chLen = termAtt.length();
      for (int i = 0; i < chLen;) {
        i += Character.toChars(
            lowerCase(charUtils.codePointAt(chArray, i)), chArray, i);
       }
      return true;
    } else {
      return false;
    }
  }
  
  private int lowerCase(int codepoint) {
    switch(codepoint) {
      /* There are two lowercase forms of sigma:
       *   U+03C2: small final sigma (end of word)
       *   U+03C3: small sigma (otherwise)
       *   
       * Standardize both to U+03C3
       */
      case '\u03C2': /* small final sigma */
        return '\u03C3'; /* small sigma */
        
      /* Some greek characters contain diacritics.
       * This filter removes these, converting to the lowercase base form.
       */
        
      case '\u0386': /* capital alpha with tonos */
      case '\u03AC': /* small alpha with tonos */
        return '\u03B1'; /* small alpha */
        
      case '\u0388': /* capital epsilon with tonos */
      case '\u03AD': /* small epsilon with tonos */
        return '\u03B5'; /* small epsilon */
        
      case '\u0389': /* capital eta with tonos */
      case '\u03AE': /* small eta with tonos */
        return '\u03B7'; /* small eta */
        
      case '\u038A': /* capital iota with tonos */
      case '\u03AA': /* capital iota with dialytika */
      case '\u03AF': /* small iota with tonos */
      case '\u03CA': /* small iota with dialytika */
      case '\u0390': /* small iota with dialytika and tonos */
        return '\u03B9'; /* small iota */
        
      case '\u038E': /* capital upsilon with tonos */
      case '\u03AB': /* capital upsilon with dialytika */
      case '\u03CD': /* small upsilon with tonos */
      case '\u03CB': /* small upsilon with dialytika */
      case '\u03B0': /* small upsilon with dialytika and tonos */
        return '\u03C5'; /* small upsilon */
        
      case '\u038C': /* capital omicron with tonos */
      case '\u03CC': /* small omicron with tonos */
        return '\u03BF'; /* small omicron */
        
      case '\u038F': /* capital omega with tonos */
      case '\u03CE': /* small omega with tonos */
        return '\u03C9'; /* small omega */
        
      /* The previous implementation did the conversion below.
       * Only implemented for backwards compatibility with old indexes.
       */
        
      case '\u03A2': /* reserved */
        return '\u03C2'; /* small final sigma */
        
      default:
        return Character.toLowerCase(codepoint);
    }
  }
}