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Lucene example source code file (CachingTokenFilter.java)

This example Lucene source code file (CachingTokenFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

cachingtokenfilter, cachingtokenfilter, io, ioexception, ioexception, override, override, tokenfilter, tokenfilter, util

The Lucene CachingTokenFilter.java source code

package org.apache.lucene.analysis;

/**
 * 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 java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import org.apache.lucene.util.AttributeSource;

/**
 * This class can be used if the token attributes of a TokenStream
 * are intended to be consumed more than once. It caches
 * all token attribute states locally in a List.
 * 
 * <P>CachingTokenFilter implements the optional method
 * {@link TokenStream#reset()}, which repositions the
 * stream to the first Token. 
 */
public final class CachingTokenFilter extends TokenFilter {
  private List<AttributeSource.State> cache = null;
  private Iterator<AttributeSource.State> iterator = null; 
  private AttributeSource.State finalState;
  
  public CachingTokenFilter(TokenStream input) {
    super(input);
  }
  
  @Override
  public final boolean incrementToken() throws IOException {
    if (cache == null) {
      // fill cache lazily
      cache = new LinkedList<AttributeSource.State>();
      fillCache();
      iterator = cache.iterator();
    }
    
    if (!iterator.hasNext()) {
      // the cache is exhausted, return false
      return false;
    }
    // Since the TokenFilter can be reset, the tokens need to be preserved as immutable.
    restoreState(iterator.next());
    return true;
  }
  
  @Override
  public final void end() throws IOException {
    if (finalState != null) {
      restoreState(finalState);
    }
  }

  @Override
  public void reset() throws IOException {
    if(cache != null) {
      iterator = cache.iterator();
    }
  }
  
  private void fillCache() throws IOException {
    while(input.incrementToken()) {
      cache.add(captureState());
    }
    // capture final state
    input.end();
    finalState = captureState();
  }

}

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