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Lucene example source code file (SimpleSpanFragmenter.java)

This example Lucene source code file (SimpleSpanFragmenter.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

chartermattribute, default_fragment_size, default_fragment_size, fragmenter, list, offsetattribute, positionincrementattribute, queryscorer, simplespanfragmenter, simplespanfragmenter, tokenstream, tokenstream, util, weightedspanterm, weightedspanterm

The Lucene SimpleSpanFragmenter.java source code

package org.apache.lucene.search.highlight;


/**
 * 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.util.List;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.search.spans.Spans;


/**
 * {@link Fragmenter} implementation which breaks text up into same-size
 * fragments but does not split up {@link Spans}. This is a simple sample class.
 */
public class SimpleSpanFragmenter implements Fragmenter {
  private static final int DEFAULT_FRAGMENT_SIZE = 100;
  private int fragmentSize;
  private int currentNumFrags;
  private int position = -1;
  private QueryScorer queryScorer;
  private int waitForPos = -1;
  private int textSize;
  private CharTermAttribute termAtt;
  private PositionIncrementAttribute posIncAtt;
  private OffsetAttribute offsetAtt;

  /**
   * @param queryScorer QueryScorer that was used to score hits
   */
  public SimpleSpanFragmenter(QueryScorer queryScorer) {
    this(queryScorer, DEFAULT_FRAGMENT_SIZE);
  }

  /**
   * @param queryScorer QueryScorer that was used to score hits
   * @param fragmentSize size in bytes of each fragment
   */
  public SimpleSpanFragmenter(QueryScorer queryScorer, int fragmentSize) {
    this.fragmentSize = fragmentSize;
    this.queryScorer = queryScorer;
  }
  
  /* (non-Javadoc)
   * @see org.apache.lucene.search.highlight.Fragmenter#isNewFragment()
   */
  public boolean isNewFragment() {
    position += posIncAtt.getPositionIncrement();

    if (waitForPos == position) {
      waitForPos = -1;
    } else if (waitForPos != -1) {
      return false;
    }

    WeightedSpanTerm wSpanTerm = queryScorer.getWeightedSpanTerm(termAtt.toString());

    if (wSpanTerm != null) {
      List<PositionSpan> positionSpans = wSpanTerm.getPositionSpans();

      for (int i = 0; i < positionSpans.size(); i++) {
        if (positionSpans.get(i).start == position) {
          waitForPos = positionSpans.get(i).end + 1;
          break;
        }
      }
    }

    boolean isNewFrag = offsetAtt.endOffset() >= (fragmentSize * currentNumFrags)
        && (textSize - offsetAtt.endOffset()) >= (fragmentSize >>> 1);
    
    if (isNewFrag) {
      currentNumFrags++;
    }

    return isNewFrag;
  }


  /* (non-Javadoc)
   * @see org.apache.lucene.search.highlight.Fragmenter#start(java.lang.String, org.apache.lucene.analysis.TokenStream)
   */
  public void start(String originalText, TokenStream tokenStream) {
    position = -1;
    currentNumFrags = 1;
    textSize = originalText.length();
    termAtt = tokenStream.addAttribute(CharTermAttribute.class);
    posIncAtt = tokenStream.addAttribute(PositionIncrementAttribute.class);
    offsetAtt = tokenStream.addAttribute(OffsetAttribute.class);
  }
}

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