lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/PerFieldAnalyzerWrapper.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.miscellaneous;


import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.DelegatingAnalyzerWrapper;

import java.util.Collections;
import java.util.Map;

/**
 * This analyzer is used to facilitate scenarios where different
 * fields require different analysis techniques.  Use the Map
 * argument in {@link #PerFieldAnalyzerWrapper(Analyzer, java.util.Map)}
 * to add non-default analyzers for fields.
 * 
 * <p>Example usage:
 * 
 * <pre class="prettyprint">
 * {@code
 * Map<String,Analyzer> analyzerPerField = new HashMap<>();
 * analyzerPerField.put("firstname", new KeywordAnalyzer());
 * analyzerPerField.put("lastname", new KeywordAnalyzer());
 *
 * PerFieldAnalyzerWrapper aWrapper =
 *   new PerFieldAnalyzerWrapper(new StandardAnalyzer(version), analyzerPerField);
 * }
 * </pre>
 * 
 * <p>In this example, StandardAnalyzer will be used for all fields except "firstname"
 * and "lastname", for which KeywordAnalyzer will be used.
 * 
 * <p>A PerFieldAnalyzerWrapper can be used like any other analyzer, for both indexing
 * and query parsing.
 *
 * @since 3.1
 */
public final class PerFieldAnalyzerWrapper extends DelegatingAnalyzerWrapper {
  private final Analyzer defaultAnalyzer;
  private final Map<String, Analyzer> fieldAnalyzers;

  /**
   * Constructs with default analyzer.
   *
   * @param defaultAnalyzer Any fields not specifically
   * defined to use a different analyzer will use the one provided here.
   */
  public PerFieldAnalyzerWrapper(Analyzer defaultAnalyzer) {
    this(defaultAnalyzer, null);
  }
  
  /**
   * Constructs with default analyzer and a map of analyzers to use for 
   * specific fields.
   *
   * @param defaultAnalyzer Any fields not specifically
   * defined to use a different analyzer will use the one provided here.
   * @param fieldAnalyzers a Map (String field name to the Analyzer) to be 
   * used for those fields 
   */
  public PerFieldAnalyzerWrapper(Analyzer defaultAnalyzer,
      Map<String, Analyzer> fieldAnalyzers) {
    super(PER_FIELD_REUSE_STRATEGY);
    this.defaultAnalyzer = defaultAnalyzer;
    this.fieldAnalyzers = (fieldAnalyzers != null) ? fieldAnalyzers : Collections.<String, Analyzer>emptyMap();
  }

  @Override
  protected Analyzer getWrappedAnalyzer(String fieldName) {
    Analyzer analyzer = fieldAnalyzers.get(fieldName);
    return (analyzer != null) ? analyzer : defaultAnalyzer;
  }

  @Override
  public String toString() {
    return "PerFieldAnalyzerWrapper(" + fieldAnalyzers + ", default=" + defaultAnalyzer + ")";
  }
}