lucene/analysis/common/src/java/org/apache/lucene/analysis/pattern/PatternReplaceFilter.java

/*
 * 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.pattern;

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

import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.io.IOException;

/**
 * A TokenFilter which applies a Pattern to each token in the stream,
 * replacing match occurrences with the specified replacement string.
 *
 * <p>
 * <b>Note:</b> Depending on the input and the pattern used and the input
 * TokenStream, this TokenFilter may produce Tokens whose text is the empty
 * string.
 * </p>
 * 
 * @see Pattern
 */
public final class PatternReplaceFilter extends TokenFilter {
  private final String replacement;
  private final boolean all;
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final Matcher m;

  /**
   * Constructs an instance to replace either the first, or all occurrences
   *
   * @param in the TokenStream to process
   * @param p the patterm to apply to each Token
   * @param replacement the "replacement string" to substitute, if null a
   *        blank string will be used. Note that this is not the literal
   *        string that will be used, '$' and '\' have special meaning.
   * @param all if true, all matches will be replaced otherwise just the first match.
   * @see Matcher#quoteReplacement
   */
  public PatternReplaceFilter(TokenStream in,
                              Pattern p,
                              String replacement,
                              boolean all) {
    super(in);
    this.replacement = (null == replacement) ? "" : replacement;
    this.all=all;
    this.m = p.matcher(termAtt);
  }

  @Override
  public boolean incrementToken() throws IOException {
    if (!input.incrementToken()) return false;
    
    m.reset();
    if (m.find()) {
      // replaceAll/replaceFirst will reset() this previous find.
      String transformed = all ? m.replaceAll(replacement) : m.replaceFirst(replacement);
      termAtt.setEmpty().append(transformed);
    }

    return true;
  }

}