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Lucene example source code file (PhraseScorer.java)

This example Lucene source code file (PhraseScorer.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, phrasepositions, phrasepositions, phrasequeue, phrasescorer, phrasescorer, scorer, similarity, string

The Lucene PhraseScorer.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;

/** Expert: Scoring functionality for phrase queries.
 * <br>A document is considered matching if it contains the phrase-query terms  
 * at "valid" positions. What "valid positions" are
 * depends on the type of the phrase query: for an exact phrase query terms are required 
 * to appear in adjacent locations, while for a sloppy phrase query some distance between 
 * the terms is allowed. The abstract method {@link #phraseFreq()} of extending classes
 * is invoked for each document containing all the phrase query terms, in order to 
 * compute the frequency of the phrase query in that document. A non zero frequency
 * means a match. 
 */
abstract class PhraseScorer extends Scorer {
  protected byte[] norms;
  protected float value;

  private boolean firstTime = true;
  private boolean more = true;
  protected PhraseQueue pq;
  protected PhrasePositions first, last;

  private float freq; //phrase frequency in current doc as computed by phraseFreq().

  PhraseScorer(Weight weight, PhraseQuery.PostingsAndFreq[] postings,
      Similarity similarity, byte[] norms) {
    super(similarity, weight);
    this.norms = norms;
    this.value = weight.getValue();

    // convert tps to a list of phrase positions.
    // note: phrase-position differs from term-position in that its position
    // reflects the phrase offset: pp.pos = tp.pos - offset.
    // this allows to easily identify a matching (exact) phrase 
    // when all PhrasePositions have exactly the same position.
    for (int i = 0; i < postings.length; i++) {
      PhrasePositions pp = new PhrasePositions(postings[i].postings, postings[i].position, i);
      if (last != null) {			  // add next to end of list
        last.next = pp;
      } else {
        first = pp;
      }
      last = pp;
    }

    pq = new PhraseQueue(postings.length);             // construct empty pq
    first.doc = -1;
  }

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

  @Override
  public int nextDoc() throws IOException {
    if (firstTime) {
      init();
      firstTime = false;
    } else if (more) {
      more = last.next();                         // trigger further scanning
    }
    if (!doNext()) {
      first.doc = NO_MORE_DOCS;
    }
    return first.doc;
  }
  
  // next without initial increment
  private boolean doNext() throws IOException {
    while (more) {
      while (more && first.doc < last.doc) {      // find doc w/ all the terms
        more = first.skipTo(last.doc);            // skip first upto last
        firstToLast();                            // and move it to the end
      }

      if (more) {
        // found a doc with all of the terms
        freq = phraseFreq();                      // check for phrase
        if (freq == 0.0f)                         // no match
          more = last.next();                     // trigger further scanning
        else
          return true;                            // found a match
      }
    }
    return false;                                 // no more matches
  }

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

  @Override
  public int advance(int target) throws IOException {
    firstTime = false;
    for (PhrasePositions pp = first; more && pp != null; pp = pp.next) {
      more = pp.skipTo(target);
    }
    if (more) {
      sort();                                     // re-sort
    }
    if (!doNext()) {
      first.doc = NO_MORE_DOCS;
    }
    return first.doc;
  }
  
  /**
   * phrase frequency in current doc as computed by phraseFreq().
   */
  @Override
  public final float freq() {
    return freq;
  }

  /**
   * For a document containing all the phrase query terms, compute the
   * frequency of the phrase in that document. 
   * A non zero frequency means a match.
   * <br>Note, that containing all phrase terms does not guarantee a match - they have to be found in matching locations.  
   * @return frequency of the phrase in current doc, 0 if not found. 
   */
  protected abstract float phraseFreq() throws IOException;

  private void init() throws IOException {
    for (PhrasePositions pp = first; more && pp != null; pp = pp.next) {
      more = pp.next();
    }
    if (more) {
      sort();
    }
  }
  
  private void sort() {
    pq.clear();
    for (PhrasePositions pp = first; pp != null; pp = pp.next) {
      pq.add(pp);
    }
    pqToList();
  }

  protected final void pqToList() {
    last = first = null;
    while (pq.top() != null) {
      PhrasePositions pp = pq.pop();
      if (last != null) {			  // add next to end of list
        last.next = pp;
      } else
        first = pp;
      last = pp;
      pp.next = null;
    }
  }

  protected final void firstToLast() {
    last.next = first;			  // move first to end of list
    last = first;
    first = first.next;
    last.next = null;
  }

  @Override
  public String toString() { return "scorer(" + weight + ")"; }
 
}

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