content: package org.apache.lucene.analysis.core;
  
  /*
   * 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.
   */
  
  import org.apache.lucene.analysis.CharacterUtils;
  import org.apache.lucene.analysis.TokenFilter;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  import org.apache.lucene.util.Version;
  
  import java.io.IOException;
  
  /**
   * Normalizes token text to lower case.
   * <p>You must specify the required {@link Version}
   * compatibility when creating LowerCaseFilter:
   * <p>
   * As of 3.1, supplementary characters are properly lowercased.
   */
  public final class SelectiveLowerCaseFilter extends TokenFilter {
      private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  
      /**
       * Create a new LowerCaseFilter, that normalizes token text to lower case.
       *
       * @param matchVersion version
       * @param in           TokenStream to filter
       */
      public SelectiveLowerCaseFilter(Version matchVersion, TokenStream in) {
          super(in);
      }
  
      @Override
      public boolean incrementToken() throws IOException {
          if (input.incrementToken()) {
              if (AcronymTokenFilter.termIsAcronym(termAtt.toString())) {
                  return true; // skip lowercasing
              }
              CharacterUtils.toLowerCase(termAtt.buffer(), 0, termAtt.length());
              return true;
  
          } else
              return false;
      }
  
  }
  