lucene/core/src/java/org/apache/lucene/analysis/AnalyzerWrapper.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;


import java.io.Reader;

import org.apache.lucene.util.AttributeFactory;

/**
 * Extension to {@link Analyzer} suitable for Analyzers which wrap
 * other Analyzers.
 * 
 * <p>{@link #getWrappedAnalyzer(String)} allows the Analyzer
 * to wrap multiple Analyzers which are selected on a per field basis.
 * 
 * <p>{@link #wrapComponents(String, Analyzer.TokenStreamComponents)} allows the
 * TokenStreamComponents of the wrapped Analyzer to then be wrapped
 * (such as adding a new {@link TokenFilter} to form new TokenStreamComponents.
 *
 * <p>{@link #wrapReader(String, Reader)} allows the Reader of the wrapped
 * Analyzer to then be wrapped (such as adding a new {@link CharFilter}.
 *
 * <p><b>Important:</b> If you do not want to wrap the TokenStream
 * using {@link #wrapComponents(String, Analyzer.TokenStreamComponents)}
 * or the Reader using {@link #wrapReader(String, Reader)} and just delegate
 * to other analyzers (like by field name), use {@link DelegatingAnalyzerWrapper}
 * as superclass!
 *
 * @see DelegatingAnalyzerWrapper
 *
 * @since 4.0.0
 */
public abstract class AnalyzerWrapper extends Analyzer {

  /**
   * Creates a new AnalyzerWrapper with the given reuse strategy.
   * <p>If you want to wrap a single delegate Analyzer you can probably
   * reuse its strategy when instantiating this subclass:
   * {@code super(delegate.getReuseStrategy());}.
   * <p>If you choose different analyzers per field, use
   * {@link #PER_FIELD_REUSE_STRATEGY}.
   * @see #getReuseStrategy()
   */
  protected AnalyzerWrapper(ReuseStrategy reuseStrategy) {
    super(reuseStrategy);
  }

  /**
   * Retrieves the wrapped Analyzer appropriate for analyzing the field with
   * the given name
   *
   * @param fieldName Name of the field which is to be analyzed
   * @return Analyzer for the field with the given name.  Assumed to be non-null
   */
  protected abstract Analyzer getWrappedAnalyzer(String fieldName);

  /**
   * Wraps / alters the given TokenStreamComponents, taken from the wrapped
   * Analyzer, to form new components. It is through this method that new
   * TokenFilters can be added by AnalyzerWrappers. By default, the given
   * components are returned.
   * 
   * @param fieldName
   *          Name of the field which is to be analyzed
   * @param components
   *          TokenStreamComponents taken from the wrapped Analyzer
   * @return Wrapped / altered TokenStreamComponents.
   */
  protected TokenStreamComponents wrapComponents(String fieldName, TokenStreamComponents components) {
    return components;
  }

  /**
   * Wraps / alters the given TokenStream for normalization purposes, taken
   * from the wrapped Analyzer, to form new components. It is through this
   * method that new TokenFilters can be added by AnalyzerWrappers. By default,
   * the given token stream are returned.
   * 
   * @param fieldName
   *          Name of the field which is to be analyzed
   * @param in
   *          TokenStream taken from the wrapped Analyzer
   * @return Wrapped / altered TokenStreamComponents.
   */
  protected TokenStream wrapTokenStreamForNormalization(String fieldName, TokenStream in) {
    return in;
  }

  /**
   * Wraps / alters the given Reader. Through this method AnalyzerWrappers can
   * implement {@link #initReader(String, Reader)}. By default, the given reader
   * is returned.
   * 
   * @param fieldName
   *          name of the field which is to be analyzed
   * @param reader
   *          the reader to wrap
   * @return the wrapped reader
   */
  protected Reader wrapReader(String fieldName, Reader reader) {
    return reader;
  }

  /**
   * Wraps / alters the given Reader. Through this method AnalyzerWrappers can
   * implement {@link #initReaderForNormalization(String, Reader)}. By default,
   * the given reader  is returned.
   * 
   * @param fieldName
   *          name of the field which is to be analyzed
   * @param reader
   *          the reader to wrap
   * @return the wrapped reader
   */
  protected Reader wrapReaderForNormalization(String fieldName, Reader reader) {
    return reader;
  }

  @Override
  protected final TokenStreamComponents createComponents(String fieldName) {
    return wrapComponents(fieldName, getWrappedAnalyzer(fieldName).createComponents(fieldName));
  }

  @Override
  protected final TokenStream normalize(String fieldName, TokenStream in) {
    return wrapTokenStreamForNormalization(fieldName, getWrappedAnalyzer(fieldName).normalize(fieldName, in));
  }

  @Override
  public int getPositionIncrementGap(String fieldName) {
    return getWrappedAnalyzer(fieldName).getPositionIncrementGap(fieldName);
  }

  @Override
  public int getOffsetGap(String fieldName) {
    return getWrappedAnalyzer(fieldName).getOffsetGap(fieldName);
  }

  @Override
  public final Reader initReader(String fieldName, Reader reader) {
    return getWrappedAnalyzer(fieldName).initReader(fieldName, wrapReader(fieldName, reader));
  }

  @Override
  protected final Reader initReaderForNormalization(String fieldName, Reader reader) {
    return getWrappedAnalyzer(fieldName).initReaderForNormalization(fieldName, wrapReaderForNormalization(fieldName, reader));
  }

  @Override
  protected final AttributeFactory attributeFactory(String fieldName) {
    return getWrappedAnalyzer(fieldName).attributeFactory(fieldName);
  }
}