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Lucene example source code file (SpanScorer.java)

This example Lucene source code file (SpanScorer.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

explanation, explanation, io, ioexception, ioexception, no_more_docs, no_more_docs, override, override, scorer, similarity, spans, spanscorer, weight

The Lucene SpanScorer.java source code

package org.apache.lucene.search.spans;

/**
 * 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 org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.Similarity;

/**
 * Public for extension only.
 */
public class SpanScorer extends Scorer {
  protected Spans spans;
  protected byte[] norms;
  protected float value;

  protected boolean more = true;

  protected int doc;
  protected float freq;

  protected SpanScorer(Spans spans, Weight weight, Similarity similarity, byte[] norms)
  throws IOException {
    super(similarity, weight);
    this.spans = spans;
    this.norms = norms;
    this.value = weight.getValue();
    if (this.spans.next()) {
      doc = -1;
    } else {
      doc = NO_MORE_DOCS;
      more = false;
    }
  }

  @Override
  public int nextDoc() throws IOException {
    if (!setFreqCurrentDoc()) {
      doc = NO_MORE_DOCS;
    }
    return doc;
  }

  @Override
  public int advance(int target) throws IOException {
    if (!more) {
      return doc = NO_MORE_DOCS;
    }
    if (spans.doc() < target) { // setFreqCurrentDoc() leaves spans.doc() ahead
      more = spans.skipTo(target);
    }
    if (!setFreqCurrentDoc()) {
      doc = NO_MORE_DOCS;
    }
    return doc;
  }
  
  protected boolean setFreqCurrentDoc() throws IOException {
    if (!more) {
      return false;
    }
    doc = spans.doc();
    freq = 0.0f;
    do {
      int matchLength = spans.end() - spans.start();
      freq += getSimilarity().sloppyFreq(matchLength);
      more = spans.next();
    } while (more && (doc == spans.doc()));
    return true;
  }

  @Override
  public int docID() { return doc; }

  @Override
  public float score() throws IOException {
    float raw = getSimilarity().tf(freq) * value; // raw score
    return norms == null? raw : raw * getSimilarity().decodeNormValue(norms[doc]); // normalize
  }
  
  @Override
  public float freq() throws IOException {
    return freq;
  }

  /** This method is no longer an official member of {@link Scorer},
   * but it is needed by SpanWeight to build an explanation. */
  protected Explanation explain(final int doc) throws IOException {
    Explanation tfExplanation = new Explanation();

    int expDoc = advance(doc);

    float phraseFreq = (expDoc == doc) ? freq : 0.0f;
    tfExplanation.setValue(getSimilarity().tf(phraseFreq));
    tfExplanation.setDescription("tf(phraseFreq=" + phraseFreq + ")");

    return tfExplanation;
  }

}

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