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Lucene example source code file (TermScorer.java)

This example Lucene source code file (TermScorer.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

io, ioexception, ioexception, no_more_docs, override, override, score_cache_size, score_cache_size, scorer, similarity, string, termdocs, termdocs, termscorer

The Lucene TermScorer.java source code

package org.apache.lucene.search;

/**
 * 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.index.TermDocs;

/** Expert: A <code>Scorer for documents matching a Term.
 */
final class TermScorer extends Scorer {
  private TermDocs termDocs;
  private byte[] norms;
  private float weightValue;
  private int doc = -1;
  private int freq;

  private final int[] docs = new int[32];         // buffered doc numbers
  private final int[] freqs = new int[32];        // buffered term freqs
  private int pointer;
  private int pointerMax;

  private static final int SCORE_CACHE_SIZE = 32;
  private float[] scoreCache = new float[SCORE_CACHE_SIZE];

  /**
   * Construct a <code>TermScorer.
   * 
   * @param weight
   *          The weight of the <code>Term in the query.
   * @param td
   *          An iterator over the documents matching the <code>Term.
   * @param similarity
   *          The </code>Similarity implementation to be used for score
   *          computations.
   * @param norms
   *          The field norms of the document fields for the <code>Term.
   */
  TermScorer(Weight weight, TermDocs td, Similarity similarity, byte[] norms) {
    super(similarity, weight);
    
    this.termDocs = td;
    this.norms = norms;
    this.weightValue = weight.getValue();

    for (int i = 0; i < SCORE_CACHE_SIZE; i++)
      scoreCache[i] = getSimilarity().tf(i) * weightValue;
  }

  @Override
  public void score(Collector c) throws IOException {
    score(c, Integer.MAX_VALUE, nextDoc());
  }

  // firstDocID is ignored since nextDoc() sets 'doc'
  @Override
  protected boolean score(Collector c, int end, int firstDocID) throws IOException {
    c.setScorer(this);
    while (doc < end) {                           // for docs in window
      c.collect(doc);                      // collect score
        
      if (++pointer >= pointerMax) {
        pointerMax = termDocs.read(docs, freqs);  // refill buffers
        if (pointerMax != 0) {
          pointer = 0;
        } else {
          termDocs.close();                       // close stream
          doc = Integer.MAX_VALUE;                // set to sentinel value
          return false;
        }
      } 
      doc = docs[pointer];
      freq = freqs[pointer];
    }
    return true;
  }

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

  @Override
  public float freq() {
    return freq;
  }

  /**
   * Advances to the next document matching the query. <br>
   * The iterator over the matching documents is buffered using
   * {@link TermDocs#read(int[],int[])}.
   * 
   * @return the document matching the query or NO_MORE_DOCS if there are no more documents.
   */
  @Override
  public int nextDoc() throws IOException {
    pointer++;
    if (pointer >= pointerMax) {
      pointerMax = termDocs.read(docs, freqs);    // refill buffer
      if (pointerMax != 0) {
        pointer = 0;
      } else {
        termDocs.close();                         // close stream
        return doc = NO_MORE_DOCS;
      }
    } 
    doc = docs[pointer];
    freq = freqs[pointer];
    return doc;
  }
  
  @Override
  public float score() {
    assert doc != -1;
    float raw =                                   // compute tf(f)*weight
      freq < SCORE_CACHE_SIZE                        // check cache
      ? scoreCache[freq]                             // cache hit
      : getSimilarity().tf(freq)*weightValue;        // cache miss

    return norms == null ? raw : raw * getSimilarity().decodeNormValue(norms[doc]); // normalize for field
  }

  /**
   * Advances to the first match beyond the current whose document number is
   * greater than or equal to a given target. <br>
   * The implementation uses {@link TermDocs#skipTo(int)}.
   * 
   * @param target
   *          The target document number.
   * @return the matching document or NO_MORE_DOCS if none exist.
   */
  @Override
  public int advance(int target) throws IOException {
    // first scan in cache
    for (pointer++; pointer < pointerMax; pointer++) {
      if (docs[pointer] >= target) {
    	freq = freqs[pointer];
        return doc = docs[pointer];
      }
    }

    // not found in cache, seek underlying stream
    boolean result = termDocs.skipTo(target);
    if (result) {
      pointerMax = 1;
      pointer = 0;
      docs[pointer] = doc = termDocs.doc();
      freqs[pointer] = freq = termDocs.freq();
    } else {
      doc = NO_MORE_DOCS;
    }
    return doc;
  }
  
  /** Returns a string representation of this <code>TermScorer. */
  @Override
  public String toString() { return "scorer(" + weight + ")"; }

}

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