lucene/analysis/common/src/java/org/apache/lucene/analysis/ngram/NGramFilterFactory.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.ngram;


import java.util.Map;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.util.TokenFilterFactory;

/**
 * Factory for {@link NGramTokenFilter}.
 * <pre class="prettyprint">
 * &lt;fieldType name="text_ngrm" class="solr.TextField" positionIncrementGap="100"&gt;
 *   &lt;analyzer&gt;
 *     &lt;tokenizer class="solr.WhitespaceTokenizerFactory"/&gt;
 *     &lt;filter class="solr.NGramFilterFactory" minGramSize="1" maxGramSize="2" preserveOriginal="true"/&gt;
 *   &lt;/analyzer&gt;
 * &lt;/fieldType&gt;</pre>
 *
 * @since 3.1
 * @lucene.spi {@value #NAME}
 */
public class NGramFilterFactory extends TokenFilterFactory {

  /** SPI name */
  public static final String NAME = "nGram";

  private final int maxGramSize;
  private final int minGramSize;
  private final boolean preserveOriginal;

  /** Creates a new NGramFilterFactory */
  public NGramFilterFactory(Map<String, String> args) {
    super(args);
    minGramSize = requireInt(args, "minGramSize");
    maxGramSize = requireInt(args, "maxGramSize");

    // First check for the old accidental used option name. It was the only way to configure preserve original
    // for NGramFilter and ignoring it would unnecessary break existing configs.
    boolean preserve = getBoolean(args, "keepShortTerm", NGramTokenFilter.DEFAULT_PRESERVE_ORIGINAL);
    preserveOriginal = getBoolean(args, "preserveOriginal", preserve);
    if (!args.isEmpty()) {
      throw new IllegalArgumentException("Unknown parameters: " + args);
    }
  }

  @Override
  public TokenFilter create(TokenStream input) {
    return new NGramTokenFilter(input, minGramSize, maxGramSize, preserveOriginal);
  }
}